Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

It could be 10 pounds of stuff and 340 pounds of shielding …

It also could be 10 pounds of WAAS and 340 pounds of something they don't want 
to talk about. 

Bob

On Jul 11, 2013, at 3:17 PM, David J Taylor  
wrote:

> If you look at the pictures here
> 
>   http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf
> 
> the satellite on the right has things sticking out the bottom, in the
> back corner, that are missing on the others and that look a lot like
> the antennas on GPS satellites.  The WAAS satellite is also 350 pounds
> heavier than the other two even though the C-band payload is identical
> on all three, so it seems like there could be a fair amount of extra
> stuff added for WAAS support.
> 
> Dennis Ferguson
> ___
> 
> Thanks, Dennis.  The antennas don't surprise me, as they would need to 
> produce a near-whole-disk coverage at a similar ground received power level 
> to the GPS satellites.  That extra weight /does/ sound a lot if it were 
> "just" a simple transponder for earth produced information.  Here in Europe 
> was have three EGNOS sources (all on other satellites, I believe), and I 
> don't believe they play any part in actual position fixing, but they do 
> provide extra information enabling the fix to be refined.
> 
> Cheers,
> David
> -- 
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-tay...@blueyonder.co.uk 
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David J Taylor]

If you look at the pictures here

   http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf

the satellite on the right has things sticking out the bottom, in the
back corner, that are missing on the others and that look a lot like
the antennas on GPS satellites.  The WAAS satellite is also 350 pounds
heavier than the other two even though the C-band payload is identical
on all three, so it seems like there could be a fair amount of extra
stuff added for WAAS support.

Dennis Ferguson
___

Thanks, Dennis.  The antennas don't surprise me, as they would need to 
produce a near-whole-disk coverage at a similar ground received power level 
to the GPS satellites.  That extra weight /does/ sound a lot if it were 
"just" a simple transponder for earth produced information.  Here in Europe 
was have three EGNOS sources (all on other satellites, I believe), and I 
don't believe they play any part in actual position fixing, but they do 
provide extra information enabling the fix to be refined.


Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

Yes, this has basically become a debate about weather WAAS sat's do or don't
contribute to a directly to a nav solution rather than just provide
correction information. 

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of David J Taylor
Sent: Thursday, July 11, 2013 12:57 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)

Hi

>From the US patent:

"... and possibility of extending the operating range by allowing increased
separation of reference and base receivers by incorporating ionospheric
models provided by WAAS"

To me that says - position data from WAAS, carrier from GPS.
===

I had understood that WAAS provided data such as what were dead or 
problematic satellites, and ionospheric data which allows the positions 
derived from standard GPS satellites to be more accurately determined 
through extra corrections, but WAAS satellite transmissions did not of 
themselves contribute to to a position determination.  Was I wrong in this, 
or perhaps outdated?

Cheers,
David
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Dennis Ferguson]

On 10 Jul, 2013, at 14:08 , David I. Emery  wrote:
> It seems completely inconceivable to me that either the antenna
> system (particularly feeds) or transponder RF hardware on any commercial
> Ku or C or Ka or X band satellite could possibly be frequency agile
> enough to tune to 1575.42 MHz unless it was purpose designed to radiate
> on that frequency from the start.
> 
>   So any hosted WAAS payload is completely application specific.

If you look at the pictures here

http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf

the satellite on the right has things sticking out the bottom, in the
back corner, that are missing on the others and that look a lot like
the antennas on GPS satellites.  The WAAS satellite is also 350 pounds
heavier than the other two even though the C-band payload is identical
on all three, so it seems like there could be a fair amount of extra
stuff added for WAAS support.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David J Taylor]

Hi


From the US patent:


"... and possibility of extending the operating range by allowing increased
separation of reference and base receivers by incorporating ionospheric
models provided by WAAS"

To me that says - position data from WAAS, carrier from GPS.
===

I had understood that WAAS provided data such as what were dead or 
problematic satellites, and ionospheric data which allows the positions 
derived from standard GPS satellites to be more accurately determined 
through extra corrections, but WAAS satellite transmissions did not of 
themselves contribute to to a position determination.  Was I wrong in this, 
or perhaps outdated?


Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

>From the US patent:

"... and possibility of extending the operating range by allowing increased
separation of reference and base receivers by incorporating ionospheric
models provided by WAAS"

To me that says - position data from WAAS, carrier from GPS.

-

I have not seen a receiver that produces pseudo range for WAAS (as opposed
to EGNOS).

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Magnus Danielson
Sent: Thursday, July 11, 2013 9:25 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)

Hi Bob,

On 07/11/2013 12:32 PM, Bob Camp wrote:
> Hi
>
> If there are no receivers using the service (WAAS as a full GPS sat), it's
either because:
>
> 1) Nobody knows about it
> 2) It does not work
>
> Either way why spend the money to keep it running much better than needed
for WAAS simply for it to be there unused?

There are receivers that produce pseudo-ranges for it [1], and hence can 
use it in nav solutions. I just found a list of such receivers. The 
typical receivers does not discloses exactly how they use the 
WAAS/EGNOS/SBAS signal beyond the obvious correction data.

There is also published works on using the WAAS and EGNOS carrier phase 
reception [2]. There is more if you dig around.

[1] Egnos User Guide. 
http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflet
s/egnos-user-guide_en.pdf

[2] US 6469663. http://www.google.com/patents/US6469663

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

Having seen the number of signals being piggybacked on some transponders (>
100,000) it's safe to say that those transponders were not running
saturated.

Bob


-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Jim Lux
Sent: Thursday, July 11, 2013 10:56 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)

On 7/11/13 3:36 AM, Bob Camp wrote:
> Hi
>
> The pseudo random spreading / looks like noise / buried signal thing is
the most common way people piggyback low level signals on a bent pipe.
>
>
Assuming that the bent pipe isn't running saturated, which I'm not sure 
is a valid assumption.  Running TWTAs with enough backoff to be 
linear(ish) consumes a lot more power.


I think that most of the transponders on commercial comsats are running 
linear (or linearized) at least for C and Ku band type applications.

However, I wouldn't be so sure for more specialized applications. 
Consider the S-band Sirius/XM system, they basically designed the 
satellites for that service, and it could be run saturated, carrying a 
single high rate data stream that the single channel ground receiver in 
the car looks at.

In fact, a bit of wikipedia research shows that each of the two Sirius 
satellite broadcasts only one carrier with 4 MHz bandwidth (different 
frequencies for different satellites). The receiver does both, to get 
diversity.  XM uses 6 frequencies, in a similar scheme.

i did find a block diagram of the Sirius payload using google in a book 
by Elbert (p 267), and while they use a huge pile of TWTAs all combined 
to radiate about a kilowatt, it does look like they're running two 
carriers through them (2322.1 and 2330.4 MHz) so they must be running at 
least somewhat linear.


Sirius is S band, but there are also L-band DARS services in other parts 
of the world. I recall seeing some of the TWTAs for these things in a 
display case at the tube mfr (Thales, these days) in Ulm, and they are 
huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes 
we use for deep space comm or earth observing radar.  A dual 300 Watt 
L-band cavity coupled TWTA is physically quite large.)


This doesn't really answer the question about what the payload for 
WAAS/EGNOS looks like, though.
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Jim Lux]

On 7/11/13 3:36 AM, Bob Camp wrote:

Hi

The pseudo random spreading / looks like noise / buried signal thing is the 
most common way people piggyback low level signals on a bent pipe.


Assuming that the bent pipe isn't running saturated, which I'm not sure 
is a valid assumption.  Running TWTAs with enough backoff to be 
linear(ish) consumes a lot more power.



I think that most of the transponders on commercial comsats are running 
linear (or linearized) at least for C and Ku band type applications.


However, I wouldn't be so sure for more specialized applications. 
Consider the S-band Sirius/XM system, they basically designed the 
satellites for that service, and it could be run saturated, carrying a 
single high rate data stream that the single channel ground receiver in 
the car looks at.


In fact, a bit of wikipedia research shows that each of the two Sirius 
satellite broadcasts only one carrier with 4 MHz bandwidth (different 
frequencies for different satellites). The receiver does both, to get 
diversity.  XM uses 6 frequencies, in a similar scheme.


i did find a block diagram of the Sirius payload using google in a book 
by Elbert (p 267), and while they use a huge pile of TWTAs all combined 
to radiate about a kilowatt, it does look like they're running two 
carriers through them (2322.1 and 2330.4 MHz) so they must be running at 
least somewhat linear.



Sirius is S band, but there are also L-band DARS services in other parts 
of the world. I recall seeing some of the TWTAs for these things in a 
display case at the tube mfr (Thales, these days) in Ulm, and they are 
huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes 
we use for deep space comm or earth observing radar.  A dual 300 Watt 
L-band cavity coupled TWTA is physically quite large.)



This doesn't really answer the question about what the payload for 
WAAS/EGNOS looks like, though.

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Magnus Danielson]

Hi Bob,

On 07/11/2013 12:32 PM, Bob Camp wrote:

Hi

If there are no receivers using the service (WAAS as a full GPS sat), it's 
either because:

1) Nobody knows about it
2) It does not work

Either way why spend the money to keep it running much better than needed for 
WAAS simply for it to be there unused?


There are receivers that produce pseudo-ranges for it [1], and hence can 
use it in nav solutions. I just found a list of such receivers. The 
typical receivers does not discloses exactly how they use the 
WAAS/EGNOS/SBAS signal beyond the obvious correction data.


There is also published works on using the WAAS and EGNOS carrier phase 
reception [2]. There is more if you dig around.


[1] Egnos User Guide. 
http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflets/egnos-user-guide_en.pdf


[2] US 6469663. http://www.google.com/patents/US6469663

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

The pseudo random spreading / looks like noise / buried signal thing is the 
most common way people piggyback low level signals on a bent pipe.

Bob

On Jul 11, 2013, at 12:00 AM, David I. Emery  wrote:

> On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
>> 
>>  But if the satellite radiates what a local GPS package would and
>> transmits ephmerides defining  its position and motion it could be
>> included in a GPS solution and could be used for timing and frequency
>> purposes the same as any other GPS satellite subject to whatever degree
>> of relative accuracy the bent pipe clock obtains and the degree to which
>> the ephemerides in the format transmitted allow an accurate position to
>> be determined.
>> 
>>  And from what I have read it seems very likely the WAAS birds 
>> meet these criteria..
> 
>   Thinking some more about the bent pipe repeater aspect of
> WAAS, aside from allowing any kind of WAAS like signal someone might
> invent in the future to be retrofitted to existing satellites without
> a long replacement cycle and expensive launches being involved - there
> are some interesting properties of the design.
> 
>   One is that one COULD bury in the WAAS uplink cryptographic
> (eg essentially random to users not in possession of the key) spreading
> sequence transmissions that would be radiated globally and could be
> received with "unique" GPS hardware... such a covert channel in civilian
> GPS could have various purposes... and would look rather noise like
> to the rest of the world.
> 
> 
> -- 
>  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

I read the patent and understand how you can get timing off of a WAAS sat. The 
carrier does not need to have fancy steering on it to enable that function. The 
thing that it does not show is doing carrier phase off of a WAAS sat.

Bob

On Jul 10, 2013, at 9:54 PM, David I. Emery  wrote:

> On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote:
>> Hi
>> 
>> If the WAAS  birds are run in a fashion that gives a true GPS payload 
>> performance, why not assign them a SN 32 or below and use them? 
>> 
>> If the WAAS birds are not in the "right numbers", why bother to set them up 
>> and spend the bucks to make them behave like a nav sat? What's the payoff?
> 
> 
>   The patent cited here recently explains... for fixed timing
> purposes and basic  anti jam a simple directional antenna pointed at the
> WAAS bird allows rejection of many interferers without elaborate and
> expensive active steered phased array nulling technology.   
> 
>   And because - given a known fixed ground position - timing and
> frequency can work with only one bird visible, this allows
> timing/frequency using just the WAAS signal (or signals, they do provide
> more than one WAAS frequency).
> 
>   And potentially if the timing accuracy via the hosted payload is
> respectable at least for the needs of many  fixed time/frequency users
> this might supply a solution MUCH less resistant to local (nearby)
> interferers than the usual more or less hemi pattern GPS antenna would -
> as fixed dishes with considerable gain toward the satellite could be
> used and in most places they would point well above the horizon and
> could be shielded by nearby structures to further reduce jamming
> susceptibility from jammers (intentional or unintentional) below or at
> the horizon for the site.   For timing/frequency users (certainly an
> important subset of the GPS user population) this provides some
> protection by antenna pattern that is hard to obtain otherwise (and
> users interested in higher precision or redundancy of timing could still
> just use another GPS timing system based on normal hemi GPS antennas as
> the primary - using the normal SVs - and rely on the dedicated dish
> pointed at the WAAS bird only as backup in the event of jamming).
> 
>   The choice of using different spreading codes from the normal
> GPS set for WAAS or using a slightly different one is an overall system
> architecture decision... which I guess was made in favor of not tying
> up codes for regular SVs for the WAAS birds.   But AFAIK a receiver with
> suitable firmware could still extract pseudo ranges and use them.
> 
>   I guess there is an issue in any frequency translation scheme
> with the relationship of carrier and code phase... a homodyne
> distortion... due to the random phase of the LO(s)...  but this too can
> be predistorted on the ground to come out right and that kept in line
> via closed loop tracking of the downlink from a ground site.
> 
>   I do understand that this insight into a potential further use
> of WAAS beyond its use as a data channel and propagation beacon seems
> to have happened later and not initially.
> 
> -- 
>  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

If there are no receivers using the service (WAAS as a full GPS sat), it's 
either because:

1) Nobody knows about it 
2) It does not work

Either way why spend the money to keep it running much better than needed for 
WAAS simply for it to be there unused?

Bob

On Jul 10, 2013, at 8:14 PM, Magnus Danielson  
wrote:

> On 07/11/2013 01:45 AM, Bob Camp wrote:
>> Hi
>> 
>> If the WAAS  birds are run in a fashion that gives a true GPS payload 
>> performance, why not assign them a SN 32 or below and use them?
>> 
>> If the WAAS birds are not in the "right numbers", why bother to set them up 
>> and spend the bucks to make them behave like a nav sat? What's the payoff?
> 
> In the old days (receiver channels are sparse resource):
> If you devote a receiver channel to receive it, let it contribute to position 
> while it provides the core corrections.
> 
> In todays world:
> Channels and GPS birds are many, WAAS only contribute to precision and 
> validation.
> 
> This assuming relatively normal commodity receivers.
> 
> The fancy receivers (double-frequency, full-blown carrier-phase 
> pseudo-ranges) had little extra use of the WAAS, except possibly somewhat 
> quicker lock-in if not being fed from a national reference grid.
> 
> Cheers,
> Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
> 
>   But if the satellite radiates what a local GPS package would and
> transmits ephmerides defining  its position and motion it could be
> included in a GPS solution and could be used for timing and frequency
> purposes the same as any other GPS satellite subject to whatever degree
> of relative accuracy the bent pipe clock obtains and the degree to which
> the ephemerides in the format transmitted allow an accurate position to
> be determined.
> 
>   And from what I have read it seems very likely the WAAS birds 
> meet these criteria..

Thinking some more about the bent pipe repeater aspect of
WAAS, aside from allowing any kind of WAAS like signal someone might
invent in the future to be retrofitted to existing satellites without
a long replacement cycle and expensive launches being involved - there
are some interesting properties of the design.

One is that one COULD bury in the WAAS uplink cryptographic
(eg essentially random to users not in possession of the key) spreading
sequence transmissions that would be radiated globally and could be
received with "unique" GPS hardware... such a covert channel in civilian
GPS could have various purposes... and would look rather noise like
to the rest of the world.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote:
> Hi
> 
> If the WAAS  birds are run in a fashion that gives a true GPS payload 
> performance, why not assign them a SN 32 or below and use them? 
> 
> If the WAAS birds are not in the "right numbers", why bother to set them up 
> and spend the bucks to make them behave like a nav sat? What's the payoff?


The patent cited here recently explains... for fixed timing
purposes and basic  anti jam a simple directional antenna pointed at the
WAAS bird allows rejection of many interferers without elaborate and
expensive active steered phased array nulling technology.   

And because - given a known fixed ground position - timing and
frequency can work with only one bird visible, this allows
timing/frequency using just the WAAS signal (or signals, they do provide
more than one WAAS frequency).

And potentially if the timing accuracy via the hosted payload is
respectable at least for the needs of many  fixed time/frequency users
this might supply a solution MUCH less resistant to local (nearby)
interferers than the usual more or less hemi pattern GPS antenna would -
as fixed dishes with considerable gain toward the satellite could be
used and in most places they would point well above the horizon and
could be shielded by nearby structures to further reduce jamming
susceptibility from jammers (intentional or unintentional) below or at
the horizon for the site.   For timing/frequency users (certainly an
important subset of the GPS user population) this provides some
protection by antenna pattern that is hard to obtain otherwise (and
users interested in higher precision or redundancy of timing could still
just use another GPS timing system based on normal hemi GPS antennas as
the primary - using the normal SVs - and rely on the dedicated dish
pointed at the WAAS bird only as backup in the event of jamming).

The choice of using different spreading codes from the normal
GPS set for WAAS or using a slightly different one is an overall system
architecture decision... which I guess was made in favor of not tying
up codes for regular SVs for the WAAS birds.   But AFAIK a receiver with
suitable firmware could still extract pseudo ranges and use them.

I guess there is an issue in any frequency translation scheme
with the relationship of carrier and code phase... a homodyne
distortion... due to the random phase of the LO(s)...  but this too can
be predistorted on the ground to come out right and that kept in line
via closed loop tracking of the downlink from a ground site.

I do understand that this insight into a potential further use
of WAAS beyond its use as a data channel and propagation beacon seems
to have happened later and not initially.

-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Magnus Danielson]

On 07/11/2013 01:45 AM, Bob Camp wrote:

Hi

If the WAAS  birds are run in a fashion that gives a true GPS payload 
performance, why not assign them a SN 32 or below and use them?

If the WAAS birds are not in the "right numbers", why bother to set them up and 
spend the bucks to make them behave like a nav sat? What's the payoff?


In the old days (receiver channels are sparse resource):
If you devote a receiver channel to receive it, let it contribute to 
position while it provides the core corrections.


In todays world:
Channels and GPS birds are many, WAAS only contribute to precision and 
validation.


This assuming relatively normal commodity receivers.

The fancy receivers (double-frequency, full-blown carrier-phase 
pseudo-ranges) had little extra use of the WAAS, except possibly 
somewhat quicker lock-in if not being fed from a national reference grid.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

If the WAAS  birds are run in a fashion that gives a true GPS payload 
performance, why not assign them a SN 32 or below and use them? 

If the WAAS birds are not in the "right numbers", why bother to set them up and 
spend the bucks to make them behave like a nav sat? What's the payoff?

Bob

On Jul 10, 2013, at 7:40 PM, "David I. Emery"  wrote:

> On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote:
>> David,
>> 
>> While I can easily see how you can do closed loop correctioin for Dopplar
>> from the transmission point for a 'bent pipe' repeater, at any other
>> location that correction would not be valid, because the paths are not
>> parallel.
> 
>   Sorry for my poor choice of words.   That is precisely what I
> meant by "for an observer on the ground it is necessary to correct for
> the satellite orbit induced doppler".This is true for ANY observer,
> since it would seem certain that the closed loop correction actually is
> structured and calculated to cause the satellite to radiate a carrier
> (and timing modulation on it) equivalent to what an accurate  local GPS
> satellite reference clock would generate if one was aboard the hosted
> payload rather than on the ground.   Anything else would make no sense
> as it is not incumbent on users to try to figure out ground relative
> timing for some unknown uplink antenna somewhere.   And offsetting
> radiated uplink time and frequency on the ground to make it right on the
> satellite at the output of the bent pipe repeater is very feasible and
> more or less a no brainer.
> 
>   But if the satellite radiates what a local GPS package would and
> transmits ephmerides defining  its position and motion it could be
> included in a GPS solution and could be used for timing and frequency
> purposes the same as any other GPS satellite subject to whatever degree
> of relative accuracy the bent pipe clock obtains and the degree to which
> the ephemerides in the format transmitted allow an accurate position to
> be determined.
> 
>   And from what I have read it seems very likely the WAAS birds 
> meet these criteria..
> 
> 
> 
> -- 
>  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
> ___
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote:
> David,
> 
> While I can easily see how you can do closed loop correctioin for Dopplar
> from the transmission point for a 'bent pipe' repeater, at any other
> location that correction would not be valid, because the paths are not
> parallel.

Sorry for my poor choice of words.   That is precisely what I
meant by "for an observer on the ground it is necessary to correct for
the satellite orbit induced doppler".This is true for ANY observer,
since it would seem certain that the closed loop correction actually is
structured and calculated to cause the satellite to radiate a carrier
(and timing modulation on it) equivalent to what an accurate  local GPS
satellite reference clock would generate if one was aboard the hosted
payload rather than on the ground.   Anything else would make no sense
as it is not incumbent on users to try to figure out ground relative
timing for some unknown uplink antenna somewhere.   And offsetting
radiated uplink time and frequency on the ground to make it right on the
satellite at the output of the bent pipe repeater is very feasible and
more or less a no brainer.

But if the satellite radiates what a local GPS package would and
transmits ephmerides defining  its position and motion it could be
included in a GPS solution and could be used for timing and frequency
purposes the same as any other GPS satellite subject to whatever degree
of relative accuracy the bent pipe clock obtains and the degree to which
the ephemerides in the format transmitted allow an accurate position to
be determined.

And from what I have read it seems very likely the WAAS birds 
meet these criteria..



-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi


On Jul 10, 2013, at 5:08 PM, David I. Emery  wrote:

> On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote:
>> On 07/09/2013 04:25 AM, Joseph Gwinn wrote:
>>> Yes, of course, but I don't think I explained very well.  The issue was
>>> more economic than technical.
>>> 
>>> There isn't much spare space, weight, or power in the birds, technology
>>> moves rapidly, and the satellite companies don't want to have expensive
>>> satellites that no longer generate rental income because something
>>> became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
>>> any possible band-limited modulation, no matter if currently known or
>>> not, and so is the safest solution.
>>> 
>>> Now WAAS may have become important enough to command dedicated
>>> hardware, but that came later, to the degree it came at all.
>> 
>> A bent pipe is more generic, but there are limits to how much you can 
>> alter the output frequency too.
> 
>   It seems completely inconceivable to me that either the antenna
> system (particularly feeds) or transponder RF hardware on any commercial
> Ku or C or Ka or X band satellite could possibly be frequency agile
> enough to tune to 1575.42 MHz unless it was purpose designed to radiate
> on that frequency from the start.
> 
>   So any hosted WAAS payload is completely application specific.
> 
>   What is not clear from anything I have read so far is whether
> the UPLINK of the modulated WAAS signal is somewhere in the normal
> (usually 6 GHz for C band satellites) uplink frequency band (probably
> off one end or the other of the frequency range used).   Seems rather
> likely that the ability to reuse the UPLINK common RF hardware
> (reflector, feeds, filters, plumbing, maybe transponder front ends and
> preamps) would make this a very natural design.
> 
>   It also seems clear that doppler and bent pipe conversion 
> oscillator correction is done closed loop by having the ground station
> that generates the uplinked WAAS signal monitor the downlink from the
> bird.

Clear from what documentation? I have not seen anything that says the WAAS is 
any better than the doppler spec. Uncorrected doppler is still *way* below the 
level on the nav sats. Why correct it?

> Obviously correcting for the uplink doppler is a matter of
> computation from knowing the bird's orbit orbit precisely, something
> that would certainly be aided by constantly monitoring the range to the
> bird from that WAAS uplink ground station and maybe another couple (for
> ionospheric corrections).   Apparently the newer stuff uses two L band
> frequencies to improve this (correct for plasma delay).   And the WAAS
> signal of course allows continuous measurement of range accurately.
> 
>   Correcting for a generally stable but slowly aging conversion
> oscillator should be pretty straightforward as well, and presumably such
> a closed loop system could hold the downlink frequency to rather tight
> tolerances given a reasonably predictable stable oscillator on the bird.
> The 240 ms up and back delay does make the loop a bit more complex, but
> the bandwidth is very low I would think since the major perturbation is
> probably thermal (satellite going into eclipse once a day at certain
> times, and changes in sun angle over a day).
> 
>   For an observer on the ground it is of course necessary to
> correct for the satellite orbit induced doppler... which can be  up to a
> couple of hundred Hz or more at 6 GHz - especially with inclined orbit
> birds such as the INMARSATs.   The downlink carrier, while more stable
> in frequency than GPS bird downlinks is hardly a highly accurate
> frequency reference on its own.   But knowing the geo bird ephemeris
> (which is broadcast on the WAAS) should allow  single signal time and
> frequency solution for an observer at an accurately known location - by
> correcting for bird movement.

That's only the first layer, you still need atmospheric correction for a low 
angle bird along with a few other things.

> 
>   How good the closed loops are relative to the precision clocks
> on GPS satellites is an interesting question, there seems to be no
> obvious design need to reach that level of stability... but it does not
> seem impossible to get pretty close.   And much of what has been
> achieved here seems related to a cost/power trade off in the hosted
> payload in regards to its reference oscillator.

I still don't see how it will be as good as a normal GPSDO, let alone better.


Bob

> 
> 
> -- 
>  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[J. Forster]

David,

While I can easily see how you can do closed loop correctioin for Dopplar
from the transmission point for a 'bent pipe' repeater, at any other
location that correction would not be valid, because the paths are not
parallel.

-John

=

> On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote:
>> On 07/09/2013 04:25 AM, Joseph Gwinn wrote:
>> >Yes, of course, but I don't think I explained very well.  The issue was
>> >more economic than technical.
>> >
>> >There isn't much spare space, weight, or power in the birds, technology
>> >moves rapidly, and the satellite companies don't want to have expensive
>> >satellites that no longer generate rental income because something
>> >became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
>> >any possible band-limited modulation, no matter if currently known or
>> >not, and so is the safest solution.
>> >
>> >Now WAAS may have become important enough to command dedicated
>> >hardware, but that came later, to the degree it came at all.
>>
>> A bent pipe is more generic, but there are limits to how much you can
>> alter the output frequency too.
>
>   It seems completely inconceivable to me that either the antenna
> system (particularly feeds) or transponder RF hardware on any commercial
> Ku or C or Ka or X band satellite could possibly be frequency agile
> enough to tune to 1575.42 MHz unless it was purpose designed to radiate
> on that frequency from the start.
>
>   So any hosted WAAS payload is completely application specific.
>
>   What is not clear from anything I have read so far is whether
> the UPLINK of the modulated WAAS signal is somewhere in the normal
> (usually 6 GHz for C band satellites) uplink frequency band (probably
> off one end or the other of the frequency range used).   Seems rather
> likely that the ability to reuse the UPLINK common RF hardware
> (reflector, feeds, filters, plumbing, maybe transponder front ends and
> preamps) would make this a very natural design.
>
>   It also seems clear that doppler and bent pipe conversion
> oscillator correction is done closed loop by having the ground station
> that generates the uplinked WAAS signal monitor the downlink from the
> bird.Obviously correcting for the uplink doppler is a matter of
> computation from knowing the bird's orbit orbit precisely, something
> that would certainly be aided by constantly monitoring the range to the
> bird from that WAAS uplink ground station and maybe another couple (for
> ionospheric corrections).   Apparently the newer stuff uses two L band
> frequencies to improve this (correct for plasma delay).   And the WAAS
> signal of course allows continuous measurement of range accurately.
>
>   Correcting for a generally stable but slowly aging conversion
> oscillator should be pretty straightforward as well, and presumably such
> a closed loop system could hold the downlink frequency to rather tight
> tolerances given a reasonably predictable stable oscillator on the bird.
> The 240 ms up and back delay does make the loop a bit more complex, but
> the bandwidth is very low I would think since the major perturbation is
> probably thermal (satellite going into eclipse once a day at certain
> times, and changes in sun angle over a day).
>
>   For an observer on the ground it is of course necessary to
> correct for the satellite orbit induced doppler... which can be  up to a
> couple of hundred Hz or more at 6 GHz - especially with inclined orbit
> birds such as the INMARSATs.   The downlink carrier, while more stable
> in frequency than GPS bird downlinks is hardly a highly accurate
> frequency reference on its own.   But knowing the geo bird ephemeris
> (which is broadcast on the WAAS) should allow  single signal time and
> frequency solution for an observer at an accurately known location - by
> correcting for bird movement.
>
>   How good the closed loops are relative to the precision clocks
> on GPS satellites is an interesting question, there seems to be no
> obvious design need to reach that level of stability... but it does not
> seem impossible to get pretty close.   And much of what has been
> achieved here seems related to a cost/power trade off in the hosted
> payload in regards to its reference oscillator.
>
>
> --
>   Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole -
> in
> celebration of what could have been, but wasn't and is not to be now
> either."
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Magnus Danielson]

On 07/10/2013 11:08 PM, David I. Emery wrote:

On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote:

On 07/09/2013 04:25 AM, Joseph Gwinn wrote:

Yes, of course, but I don't think I explained very well.  The issue was
more economic than technical.

There isn't much spare space, weight, or power in the birds, technology
moves rapidly, and the satellite companies don't want to have expensive
satellites that no longer generate rental income because something
became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
any possible band-limited modulation, no matter if currently known or
not, and so is the safest solution.

Now WAAS may have become important enough to command dedicated
hardware, but that came later, to the degree it came at all.


A bent pipe is more generic, but there are limits to how much you can
alter the output frequency too.


It seems completely inconceivable to me that either the antenna
system (particularly feeds) or transponder RF hardware on any commercial
Ku or C or Ka or X band satellite could possibly be frequency agile
enough to tune to 1575.42 MHz unless it was purpose designed to radiate
on that frequency from the start.

So any hosted WAAS payload is completely application specific.


I was thinking along the same lines, but I have too little experience in 
RF design for birds. There are several potential other uses for L-band 
transmission if tweaking a little up or down from L1 is feasible, 
otherwise it's pretty application specific.


WAAS links primarily provides an information channel, so it doesn't have 
to be very accurate. However, as you devote a channel to it, you might 
as well use it to produce pseudo-ranges, but it seems like they didn't 
care too much on the carrier-phase part compared to the code-phase, but 
10 years back not many receivers used the code phase for nav at all, but 
carrier smoothed code should at least be common now, so for those it may 
not fully meet the needs. The added precision for the other channels 
compensate thought.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[David I. Emery]

On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote:
> On 07/09/2013 04:25 AM, Joseph Gwinn wrote:
> >Yes, of course, but I don't think I explained very well.  The issue was
> >more economic than technical.
> >
> >There isn't much spare space, weight, or power in the birds, technology
> >moves rapidly, and the satellite companies don't want to have expensive
> >satellites that no longer generate rental income because something
> >became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
> >any possible band-limited modulation, no matter if currently known or
> >not, and so is the safest solution.
> >
> >Now WAAS may have become important enough to command dedicated
> >hardware, but that came later, to the degree it came at all.
> 
> A bent pipe is more generic, but there are limits to how much you can 
> alter the output frequency too.

It seems completely inconceivable to me that either the antenna
system (particularly feeds) or transponder RF hardware on any commercial
Ku or C or Ka or X band satellite could possibly be frequency agile
enough to tune to 1575.42 MHz unless it was purpose designed to radiate
on that frequency from the start.

So any hosted WAAS payload is completely application specific.

What is not clear from anything I have read so far is whether
the UPLINK of the modulated WAAS signal is somewhere in the normal
(usually 6 GHz for C band satellites) uplink frequency band (probably
off one end or the other of the frequency range used).   Seems rather
likely that the ability to reuse the UPLINK common RF hardware
(reflector, feeds, filters, plumbing, maybe transponder front ends and
preamps) would make this a very natural design.

It also seems clear that doppler and bent pipe conversion 
oscillator correction is done closed loop by having the ground station
that generates the uplinked WAAS signal monitor the downlink from the
bird.Obviously correcting for the uplink doppler is a matter of
computation from knowing the bird's orbit orbit precisely, something
that would certainly be aided by constantly monitoring the range to the
bird from that WAAS uplink ground station and maybe another couple (for
ionospheric corrections).   Apparently the newer stuff uses two L band
frequencies to improve this (correct for plasma delay).   And the WAAS
signal of course allows continuous measurement of range accurately.

Correcting for a generally stable but slowly aging conversion
oscillator should be pretty straightforward as well, and presumably such
a closed loop system could hold the downlink frequency to rather tight
tolerances given a reasonably predictable stable oscillator on the bird.
The 240 ms up and back delay does make the loop a bit more complex, but
the bandwidth is very low I would think since the major perturbation is
probably thermal (satellite going into eclipse once a day at certain
times, and changes in sun angle over a day).

For an observer on the ground it is of course necessary to
correct for the satellite orbit induced doppler... which can be  up to a
couple of hundred Hz or more at 6 GHz - especially with inclined orbit
birds such as the INMARSATs.   The downlink carrier, while more stable
in frequency than GPS bird downlinks is hardly a highly accurate
frequency reference on its own.   But knowing the geo bird ephemeris
(which is broadcast on the WAAS) should allow  single signal time and
frequency solution for an observer at an accurately known location - by
correcting for bird movement.

How good the closed loops are relative to the precision clocks
on GPS satellites is an interesting question, there seems to be no
obvious design need to reach that level of stability... but it does not
seem impossible to get pretty close.   And much of what has been
achieved here seems related to a cost/power trade off in the hosted
payload in regards to its reference oscillator.


-- 
  Dave Emery N1PRE/AE, d...@dieconsulting.com  DIE Consulting, Weston, Mass 
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Magnus Danielson]

On 07/09/2013 04:25 AM, Joseph Gwinn wrote:

Yes, of course, but I don't think I explained very well.  The issue was
more economic than technical.

There isn't much spare space, weight, or power in the birds, technology
moves rapidly, and the satellite companies don't want to have expensive
satellites that no longer generate rental income because something
became obsolete.  So they ruthlessly simplify.  A bent pipe will handle
any possible band-limited modulation, no matter if currently known or
not, and so is the safest solution.

Now WAAS may have become important enough to command dedicated
hardware, but that came later, to the degree it came at all.


A bent pipe is more generic, but there are limits to how much you can 
alter the output frequency too.


If the payload is long-term contracted already when the bird is in the 
planning stage, then it is another issue.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Joseph Gwinn]

Re: time-nuts Digest, Vol 108, Issue 36
On Sat, 06 Jul 2013 13:59:26 -0400, time-nuts-requ...@febo.com wrote:

> 
> Message: 5
> Date: Sat, 06 Jul 2013 18:57:05 +0200
> From: Magnus Danielson 
> To: time-nuts@febo.com
> Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
> Message-ID: <51d84c61.3070...@rubidium.dyndns.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 07/06/2013 06:29 PM, Joseph Gwinn wrote:
>>>> Code/Carrier Frequency Coherence: The lack of coherence between the
>>>> broadcast carrier phase and the code phase shall be limited. The short
>>>> term (<10sec) fractional frequency difference between the code phase
>>>> rate and the carrier frequency shall be less than 5x10-11 (one sigma).
>>>> Over the long term (<100 sec), the difference between the change in the
>>>> broadcast code phase (convert to carrier cycles) and the change in the
>>>> broadcast carrier phase shall be within one carrier cycle (one sigma).
>>> 
>>> 
>>> This is interesting. Does it imply that they regenerate the code on board?
>> 
>> Very unlikely, because then the bird would have to understand every
>> possible code, including those not invented when the bird was launched.
> 
> If it is within the Gold codes being used for GPS and WAAS, they only 
> need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
> specification, as this method is being recommended for receivers.
> 
> Within that limit, it is relatively cheap to provide code tunability.

Yes, of course, but I don't think I explained very well.  The issue was 
more economic than technical.   

There isn't much spare space, weight, or power in the birds, technology 
moves rapidly, and the satellite companies don't want to have expensive 
satellites that no longer generate rental income because something 
became obsolete.  So they ruthlessly simplify.  A bent pipe will handle 
any possible band-limited modulation, no matter if currently known or 
not, and so is the safest solution.

Now WAAS may have become important enough to command dedicated 
hardware, but that came later, to the degree it came at all.

Joe Gwinn
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

I have a dish. I have several GPSDOs, some I built myself. I just think it 
would be a fun thing to try. It will not beat the performance of my GPSDOs 
or rubidium oscillators. Someone with a micrometer still has use for a yard 
stick. Yesterday, I worked on the dish feed. I checked the polarization 
sense and figured out a way to mount it to the dish. Next week or early 
August, I hope to have made an adjustable elevation/azimuth mount for the 
dish. Maybe by fall I could have some interesting results to share.


Just having fun with time science. Heck, I even toy with tuning fork 
oscillators and I hope to build a nice pendulum clock myself someday!


John  WA4WDL

--
From: "Bob Camp" 
Sent: Saturday, July 06, 2013 10:23 PM
To: "Discussion of precise time and frequency measurement" 


Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


Hi

Ok, lets *assume* there is some uber secret gizmo in the sat that makes 
the unsupervised signal absolutely perfect when transmitted from the sat.


The sat still moves relative to the ground. It's speed is a vector in 
three dimensions (up / down , north / south, east / west). Depending on 
your location relative to the sat, the doppler will be different.


A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. 
It'll do much better over long time spans. At 1.5 GHz, that would be 0.015 
Hz.


If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1 
simply to get the carrier as good as a simple GPSDO. That's going to 
require accurate position data on the sat, it's velocity (all real time), 
and your location.


-

Next you need data on the rest of the constellation. They fly in the same 
space as the WAAS birds, and transmit on the same frequencies. As they 
pass within the capture area of your antenna you will need a way to figure 
out which is the GPS and which is the WAAS sat.


The easy way to do that would be to run a GPS to get all the data and then 
process it…..




Dish costs something
Downconverter costs something
Signal processing the received signal costs something
You still need a GPS
You still need a good local OCXO as a flywheel

It's going to be tough to convince me that's any cheaper than a GPSDO

-

Lots of things to slog through. I suspect there are other sat signals that 
are better candidates.


Bob


On Jul 6, 2013, at 2:23 PM, jmfranke  wrote:


A lot of the changes from "bent pipe" to the new system including C-band
uplink is explained here:

http://www.insidegnss.com/node/697


While there, downlink the extended PDF version.

John  WA4WDL


--
From: "Magnus Danielson" 
Sent: Saturday, July 06, 2013 12:57 PM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


On 07/06/2013 06:29 PM, Joseph Gwinn wrote:

Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The 
short

term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one 
sigma).
Over the long term (<100 sec), the difference between the change in 
the
broadcast code phase (convert to carrier cycles) and the change in 
the
broadcast carrier phase shall be within one carrier cycle (one 
sigma).



This is interesting. Does it imply that they regenerate the code on 
board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.


If it is within the Gold codes being used for GPS and WAAS, they only 
need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
specification, as this method is being recommended for receivers.


Within that limit, it is relatively cheap to provide code tunability.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[bg]

Hi everyone,

Have not seen a reference to either the Fenton patent nor the Fruehof
paper, which discuss using WAAS for timing with a dish antenna.

http://www.freqelec.com/gps_gnss/waas_for_telecom_wp_5-06.pdf
https://www.google.com/patents/US6445340

kind regards,

Björn

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[ewkehren]

Jim, you are patialy correct but 99% only talk, never build any thing
Bert Kehren




Sent from Samsung tabletJim Lux  wrote:On 7/6/13 7:23 PM, 
Bob Camp wrote:
> Hi
>
> Ok, lets *assume* there is some uber secret gizmo in the sat that makes the 
> unsupervised signal absolutely perfect when transmitted from the sat.
>
> The sat still moves relative to the ground. It's speed is a vector in three 
> dimensions (up / down , north / south, east / west). Depending on your 
> location relative to the sat, the doppler will be different.
>
> A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll 
> do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz.
>
> If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1 
> simply to get the carrier as good as a simple GPSDO. That's going to require 
> accurate position data on the sat, it's velocity (all real time), and your 
> location.
>
> -
>
> Next you need data on the rest of the constellation. They fly in the same 
> space as the WAAS birds, and transmit on the same frequencies. As they pass 
> within the capture area of your antenna you will need a way to figure out 
> which is the GPS and which is the WAAS sat.
>
> The easy way to do that would be to run a GPS to get all the data and then 
> process it…..
>
> 
>
> Dish costs something
> Downconverter costs something
> Signal processing the received signal costs something
> You still need a GPS
> You still need a good local OCXO as a flywheel
>
> It's going to be tough to convince me that's any cheaper than a GPSDO
>



I think you're right..

But time-nuts don't always go for the "easy" way..


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Jim Lux]

On 7/6/13 7:23 PM, Bob Camp wrote:

Hi

Ok, lets *assume* there is some uber secret gizmo in the sat that makes the 
unsupervised signal absolutely perfect when transmitted from the sat.

The sat still moves relative to the ground. It's speed is a vector in three 
dimensions (up / down , north / south, east / west). Depending on your location 
relative to the sat, the doppler will be different.

A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll 
do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz.

If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1 
simply to get the carrier as good as a simple GPSDO. That's going to require 
accurate position data on the sat, it's velocity (all real time), and your 
location.

-

Next you need data on the rest of the constellation. They fly in the same space 
as the WAAS birds, and transmit on the same frequencies. As they pass within 
the capture area of your antenna you will need a way to figure out which is the 
GPS and which is the WAAS sat.

The easy way to do that would be to run a GPS to get all the data and then 
process it…..



Dish costs something
Downconverter costs something
Signal processing the received signal costs something
You still need a GPS
You still need a good local OCXO as a flywheel

It's going to be tough to convince me that's any cheaper than a GPSDO





I think you're right..

But time-nuts don't always go for the "easy" way..


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Bob Camp]

Hi

Ok, lets *assume* there is some uber secret gizmo in the sat that makes the 
unsupervised signal absolutely perfect when transmitted from the sat. 

The sat still moves relative to the ground. It's speed is a vector in three 
dimensions (up / down , north / south, east / west). Depending on your location 
relative to the sat, the doppler will be different. 

A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll 
do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz.

If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1 
simply to get the carrier as good as a simple GPSDO. That's going to require 
accurate position data on the sat, it's velocity (all real time), and your 
location. 

-

Next you need data on the rest of the constellation. They fly in the same space 
as the WAAS birds, and transmit on the same frequencies. As they pass within 
the capture area of your antenna you will need a way to figure out which is the 
GPS and which is the WAAS sat. 

The easy way to do that would be to run a GPS to get all the data and then 
process it…..



Dish costs something 
Downconverter costs something 
Signal processing the received signal costs something
You still need a GPS
You still need a good local OCXO as a flywheel 

It's going to be tough to convince me that's any cheaper than a GPSDO

-

Lots of things to slog through. I suspect there are other sat signals that are 
better candidates.

Bob


On Jul 6, 2013, at 2:23 PM, jmfranke  wrote:

> A lot of the changes from "bent pipe" to the new system including C-band
> uplink is explained here:
> 
> http://www.insidegnss.com/node/697
> 
> 
> While there, downlink the extended PDF version.
> 
> John  WA4WDL
> 
> 
> --
> From: "Magnus Danielson" 
> Sent: Saturday, July 06, 2013 12:57 PM
> To: 
> Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
> 
>> On 07/06/2013 06:29 PM, Joseph Gwinn wrote:
>>>>> Code/Carrier Frequency Coherence: The lack of coherence between the
>>>>> broadcast carrier phase and the code phase shall be limited. The short
>>>>> term (<10sec) fractional frequency difference between the code phase
>>>>> rate and the carrier frequency shall be less than 5x10-11 (one sigma).
>>>>> Over the long term (<100 sec), the difference between the change in the
>>>>> broadcast code phase (convert to carrier cycles) and the change in the
>>>>> broadcast carrier phase shall be within one carrier cycle (one sigma).
>>>> 
>>>> 
>>>> This is interesting. Does it imply that they regenerate the code on board?
>>> 
>>> Very unlikely, because then the bird would have to understand every
>>> possible code, including those not invented when the bird was launched.
>> 
>> If it is within the Gold codes being used for GPS and WAAS, they only need 
>> to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
>> specification, as this method is being recommended for receivers.
>> 
>> Within that limit, it is relatively cheap to provide code tunability.
>> 
>> Cheers,
>> Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Jim Lux]

On 7/6/13 9:29 AM, Joseph Gwinn wrote:


Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in the
broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.



the class of codes used is pretty restricted (e.g. Gold/Kasami codes 
with 10 bit generators), at least for GPS.  Most correlator and 
generator implementations are somewhat programmable, at  least as far as 
the tap configuration and the initial load.



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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

Sorry about the duplicates, email issue.

John  WA4WDL 


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

A lot of the changes from "bent pipe" to the new system including C-band 
uplink is explained here:


http://www.insidegnss.com/node/697


While there, downlink the extended PDF version.

John  WA4WDL
--
From: "Magnus Danielson" 
Sent: Saturday, July 06, 2013 12:57 PM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


On 07/06/2013 06:29 PM, Joseph Gwinn wrote:

Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in the
broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on 
board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.


If it is within the Gold codes being used for GPS and WAAS, they only need 
to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
specification, as this method is being recommended for receivers.


Within that limit, it is relatively cheap to provide code tunability.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

--
From: "jmfranke" 
Sent: Saturday, July 06, 2013 2:09 PM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)

A lot of the changes from "bent pipe" to the new system including C-band 
uplink is explained here:


http://www.insidegnss.com/node/697


While there, downlink the extended PDF version.

John  WA4WDL
--
From: "Magnus Danielson" 
Sent: Saturday, July 06, 2013 12:57 PM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


On 07/06/2013 06:29 PM, Joseph Gwinn wrote:

Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in 
the

broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on 
board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.


If it is within the Gold codes being used for GPS and WAAS, they only 
need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
specification, as this method is being recommended for receivers.


Within that limit, it is relatively cheap to provide code tunability.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

A lot of the changes from "bent pipe" to the new system including C-band
uplink is explained here:

http://www.insidegnss.com/node/697


While there, downlink the extended PDF version.

John  WA4WDL


--
From: "Magnus Danielson" 
Sent: Saturday, July 06, 2013 12:57 PM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


On 07/06/2013 06:29 PM, Joseph Gwinn wrote:

Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in the
broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on 
board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.


If it is within the Gold codes being used for GPS and WAAS, they only need 
to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
specification, as this method is being recommended for receivers.


Within that limit, it is relatively cheap to provide code tunability.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Magnus Danielson]

On 07/06/2013 06:29 PM, Joseph Gwinn wrote:

Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in the
broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on board?


Very unlikely, because then the bird would have to understand every
possible code, including those not invented when the bird was launched.


If it is within the Gold codes being used for GPS and WAAS, they only 
need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
specification, as this method is being recommended for receivers.


Within that limit, it is relatively cheap to provide code tunability.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Joseph Gwinn]

Re: time-nuts Digest, Vol 108, Issue 35
On Sat, 06 Jul 2013 12:00:01 -0400, time-nuts-requ...@febo.com wrote:

> Message: 5
> Date: Sat, 06 Jul 2013 08:56:46 -0700
> From: Jim Lux 
> To: time-nuts@febo.com
> Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
> Message-ID: <51d83e3e.2050...@earthlink.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 7/6/13 8:10 AM, jmfranke wrote:
>> http://www.navipedia.net/index.php/WAAS_Signal_Structure
>> 
>> Doppler Shift: The Doppler shift, as perceived by a stationary user, on
>> the signal broadcast by WAAS GEOs is less than 40 meters per second
>> (?210 Hz at L1) in the worst case (at the end of life of the GEOs).
> 
> That is more a requirement on the spacecraft.  Precompensation from the 
> ground won't work... if the satellite is driving West, then users to the 
> west see the frequency go up, and users to the east see it go down.
> 
>> Carrier Frequency Stability: The short term stability of the carrier
>> frequency (square root of the Allan Variance) at the input of the user?s
>> receiver antenna will be better than 5x10-11 over 1 to 10 seconds,
>> excluding the effects of the ionosphere and Doppler.
> 
> that sounds like comparable to a decent OCXO (10811A, etc.)
> 
> 
>> Polarization: The broadcast signal is right-handed circularly polarized.
>> The ellipticity will be no worse than 2 dB for the angular range of
>> ?9.1o from boresight.
> 
> Antenna spec..
> 
>> Code/Carrier Frequency Coherence: The lack of coherence between the
>> broadcast carrier phase and the code phase shall be limited. The short
>> term (<10sec) fractional frequency difference between the code phase
>> rate and the carrier frequency shall be less than 5x10-11 (one sigma).
>> Over the long term (<100 sec), the difference between the change in the
>> broadcast code phase (convert to carrier cycles) and the change in the
>> broadcast carrier phase shall be within one carrier cycle (one sigma).
> 
> 
> This is interesting. Does it imply that they regenerate the code on board?

Very unlikely, because then the bird would have to understand every 
possible code, including those not invented when the bird was launched.

Joe Gwinn
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Jim Lux]

On 7/6/13 7:50 AM, Joseph Gwinn wrote:

Re: time-nuts Digest, Vol 108, Issue 29
On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote:



OK.  Given that the birds WAAS uses were built for communications
purposes, not timing purposes, I'g guess that their frequency reference
is a very good quartz unit. I suppose Rubidium is possible, but Cesium
is very unlikely.



Except that apparently, the WAAS/EGNOS repeater payload is purpose 
designed, so it isn't necessarily the "same" bent pipe as is used for 
other purposes, although it could be: similar to other Mobile Satellite 
Service channels for instance.


I would think it very unlikely they are flying either Rb or Cs.  If they 
need high stability and precision, then they'd just recover the carrier 
from the uplink signal, because that could be as steady as you like it. 
 I would think it would be cheaper to do that than to put an atomic 
reference up.





Bent-pipe channels do a frequency change to eliminate singing.  I
imagine the datasheet for the rentable comm channels will give the
frequency error and stability of the downlink signal.


The international allocations for up and down frequencies are separated 
by quite a bit (Earth to Space and Space to Earth, respectively).


For C band, up is around 6 GHz and down is around 4 GHz.  That makes 
building a filter to separate them pretty easy. So the WAAS signal goes 
up on 4 and comes down on 1.5.


What is really needed is a good description of the WAAS/EGNOS system, 
because it will give all those nice gory details.


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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Jim Lux]

On 7/6/13 8:10 AM, jmfranke wrote:

http://www.navipedia.net/index.php/WAAS_Signal_Structure

Doppler Shift: The Doppler shift, as perceived by a stationary user, on
the signal broadcast by WAAS GEOs is less than 40 meters per second
(?210 Hz at L1) in the worst case (at the end of life of the GEOs).


That is more a requirement on the spacecraft.  Precompensation from the 
ground won't work... if the satellite is driving West, then users to the 
west see the frequency go up, and users to the east see it go down.



Carrier Frequency Stability: The short term stability of the carrier
frequency (square root of the Allan Variance) at the input of the user´s
receiver antenna will be better than 5x10-11 over 1 to 10 seconds,
excluding the effects of the ionosphere and Doppler.


that sounds like comparable to a decent OCXO (10811A, etc.)



Polarization: The broadcast signal is right-handed circularly polarized.
The ellipticity will be no worse than 2 dB for the angular range of
±9.1o from boresight.


Antenna spec..


Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short
term (<10sec) fractional frequency difference between the code phase
rate and the carrier frequency shall be less than 5x10-11 (one sigma).
Over the long term (<100 sec), the difference between the change in the
broadcast code phase (convert to carrier cycles) and the change in the
broadcast carrier phase shall be within one carrier cycle (one sigma).



This is interesting. Does it imply that they regenerate the code on board?

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Re: [time-nuts] Speaking of Costas loops (WAAS)

[jmfranke]

http://www.navipedia.net/index.php/WAAS_Signal_Structure

Doppler Shift: The Doppler shift, as perceived by a stationary user, on the 
signal broadcast by WAAS GEOs is less than 40 meters per second (?210 Hz at 
L1) in the worst case (at the end of life of the GEOs).
Carrier Frequency Stability: The short term stability of the carrier 
frequency (square root of the Allan Variance) at the input of the user´s 
receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding 
the effects of the ionosphere and Doppler.
Polarization: The broadcast signal is right-handed circularly polarized. The 
ellipticity will be no worse than 2 dB for the angular range of ±9.1o from 
boresight.
Code/Carrier Frequency Coherence: The lack of coherence between the 
broadcast carrier phase and the code phase shall be limited. The short term 
(<10sec) fractional frequency difference between the code phase rate and the 
carrier frequency shall be less than 5x10-11 (one sigma). Over the long term 
(<100 sec), the difference between the change in the broadcast code phase 
(convert to carrier cycles) and the change in the broadcast carrier phase 
shall be within one carrier cycle (one sigma).
Correlation Loss: Correlation loss is defined as the ratio of output powers 
from a perfect correlator for two cases: 1) the actual receiver WAAS signal 
correlated against a perfect unfiltered PN reference, or 2) a perfect 
unfiltered PN signal normalized to the same total power as the WAAS signal 
in case 1. The correlation loss resulting from modulation imperfections and 
filtering inside the WAAS satellite payload is less than 1 dB.


John  WA4WDL

--
From: "Joseph Gwinn" 
Sent: Saturday, July 06, 2013 10:50 AM
To: 
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)


Re: time-nuts Digest, Vol 108, Issue 29
On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote:


Message: 6
Date: Sat, 06 Jul 2013 00:27:33 +0200
From: Magnus Danielson 
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops
Message-ID: <51d74855.9090...@rubidium.dyndns.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 07/05/2013 10:39 PM, Joseph Gwinn wrote:

Re: time-nuts Digest, Vol 108, Issue 28
Message: 2
Date: Fri, 05 Jul 2013 09:18:39 -0700
From: Jim Lux
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops
Message-ID:<51d6f1df.9090...@earthlink.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 7/5/13 8:44 AM, Bob Stewart wrote:

Wouldn't a Cs or Rb clock in orbit be slow due to relativistic
effects?  I'm pretty sure there is a relativistic correction to the
GPS clocks.

Bob - AE6RV




I believe that the original WAAS repurposed transponders intended for
other L-band satellite signals (e.g. Sirius/XM/LightSquared).

As noted earlier in the discussion, the new satellites might have a
specialized payload, which could have a purpose specific coherent
transponder, rather than a linear translator.

If it is purpose specific and single channel, then making it immune to
the local oscillator is straightforward.


I worked on a proposal for the original WAAS system.  The WAAS signal
is not a timing signal in the sense that GPS signals from space are
timing signals.  WAAS instead sends out a stream of correction data
that allows one to greatly improve the accuracy and reliability of GPS
signals.

So, unless things have changed greatly, the geostationary satellite
that broadcasts the WAAS signal need not have an atomic clock.


This is naturally still true, but we are into the level of "there's a
signal here, what can we use it for?". Doing a much simplified receiver
could serve some well enough, without going the full monty. It's like
taking the color-carrier of analog TV broadcasts.


OK.  Given that the birds WAAS uses were built for communications
purposes, not timing purposes, I'g guess that their frequency reference
is a very good quartz unit. I suppose Rubidium is possible, but Cesium
is very unlikely.

Bent-pipe channels do a frequency change to eliminate singing.  I
imagine the datasheet for the rentable comm channels will give the
frequency error and stability of the downlink signal.

Joe Gwinn
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Re: [time-nuts] Speaking of Costas loops (WAAS)

[Joseph Gwinn]

> Re: time-nuts Digest, Vol 108, Issue 29
> On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote:
>
> 
> Message: 6
> Date: Sat, 06 Jul 2013 00:27:33 +0200
> From: Magnus Danielson 
> To: time-nuts@febo.com
> Subject: Re: [time-nuts] Speaking of Costas loops
> Message-ID: <51d74855.9090...@rubidium.dyndns.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 07/05/2013 10:39 PM, Joseph Gwinn wrote:
>>> Re: time-nuts Digest, Vol 108, Issue 28
>>> Message: 2
>>> Date: Fri, 05 Jul 2013 09:18:39 -0700
>>> From: Jim Lux
>>> To: time-nuts@febo.com
>>> Subject: Re: [time-nuts] Speaking of Costas loops
>>> Message-ID:<51d6f1df.9090...@earthlink.net>
>>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>> 
>>> On 7/5/13 8:44 AM, Bob Stewart wrote:
>>>> Wouldn't a Cs or Rb clock in orbit be slow due to relativistic
>>>> effects?  I'm pretty sure there is a relativistic correction to the
>>>> GPS clocks.
>>>> 
>>>> Bob - AE6RV
>>>> 
>>>> 
>>> 
>>> I believe that the original WAAS repurposed transponders intended for
>>> other L-band satellite signals (e.g. Sirius/XM/LightSquared).
>>> 
>>> As noted earlier in the discussion, the new satellites might have a
>>> specialized payload, which could have a purpose specific coherent
>>> transponder, rather than a linear translator.
>>> 
>>> If it is purpose specific and single channel, then making it immune to
>>> the local oscillator is straightforward.
>> 
>> I worked on a proposal for the original WAAS system.  The WAAS signal
>> is not a timing signal in the sense that GPS signals from space are
>> timing signals.  WAAS instead sends out a stream of correction data
>> that allows one to greatly improve the accuracy and reliability of GPS
>> signals.
>> 
>> So, unless things have changed greatly, the geostationary satellite
>> that broadcasts the WAAS signal need not have an atomic clock.
> 
> This is naturally still true, but we are into the level of "there's a 
> signal here, what can we use it for?". Doing a much simplified receiver 
> could serve some well enough, without going the full monty. It's like 
> taking the color-carrier of analog TV broadcasts.

OK.  Given that the birds WAAS uses were built for communications 
purposes, not timing purposes, I'g guess that their frequency reference 
is a very good quartz unit. I suppose Rubidium is possible, but Cesium 
is very unlikely.  

Bent-pipe channels do a frequency change to eliminate singing.  I 
imagine the datasheet for the rentable comm channels will give the 
frequency error and stability of the downlink signal.

Joe Gwinn
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Re: [time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/5/13 11:37 AM, Attila Kinali wrote:

On Fri, 5 Jul 2013 12:14:20 -0400
Bob Camp  wrote:


Indeed the atomic clocks on sats are set up so they can "tune" far
enough to take out the relativistic effects. That (and a bunch of other
things) makes them somewhat more expensive than their ground based cousins
(like by 10-100X).


Something being space qualified already makes it 10-100 times more expensive.
A "simple" FET costs easily 100USD, 1000USD is not unheard of.


the component is still <$10. It's the pallet load of paperwork that 
accompanies that component, and the burden on the manufacturer(s) of 
"traceability to sand"  (I suppose we have to change that phrase.. not 
much Gallium, Indium, etc. in sand)


That is changing though.  Class S and V parts are getting harder and 
harder to find, and the space biz is definitely moving towards more 
"industrial" parts. AFter all, the required failure rates for components 
used in engine control units for cars are substantially better than 
those traditionally required for spaceflight.


It's more a matter of understanding what might go wrong, than the actual 
probability of it going wrong.


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Re: [time-nuts] Speaking of Costas loops

[jmfranke]

Exactly! It just seems like an interesting set of facts. I plan on doing 
some more work on my WAAS dish antenna tomorrow.


John  WA4WDL

--
From: "Dennis Ferguson" 
Sent: Friday, July 05, 2013 7:55 PM
To: "Discussion of precise time and frequency measurement" 


Subject: Re: [time-nuts] Speaking of Costas loops



On 5 Jul, 2013, at 08:33 , Bob Camp  wrote:
The sat needs to transmit at the GPS frequencies and have an uplink that 
works exclusively with those frequencies. (or at least that sub band). A 
"normal" transponder probably would not radiate at the GPS allocation, 
simply to be a good citizen. I believe the "specialization" is simply a 
frequency mod to allow WAAS to pass through. There is no mention of a 
space qualified Cs and / or Rb flying on those birds and no indication 
that the ground segment is controlling such a payload. If all that *was* 
present, then including them in the normal navigation solutions would be 
a "zero cost" next step.


Addressing the last sentence I found a government WAAS reference
which indicates that the WAAS satellites are indeed interchangeable
with GPS satellites in navigation solutions.  It is is on page 7 of
this

   http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf

where it says

   The WAAS GEO broadcast also provides an additional ranging source
   for improved availability of navigation services. When a WAAS receiver
   is using the corrections and integrity messages broadcast by the GEO,
   only four GPS or GEO satellites are needed, which increases the
   availability of service versus RAIM or RAIM/FDE.

While what is or isn't required in the satellite to support this is
still a mystery it seems like the timing accuracy coming back must
end up being equivalent to a real GPS satellite.  What this is good
for is interesting to think about.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Dennis Ferguson]

On 5 Jul, 2013, at 08:33 , Bob Camp  wrote:
> The sat needs to transmit at the GPS frequencies and have an uplink that 
> works exclusively with those frequencies. (or at least that sub band). A 
> "normal" transponder probably would not radiate at the GPS allocation, simply 
> to be a good citizen. I believe the "specialization" is simply a frequency 
> mod to allow WAAS to pass through. There is no mention of a space qualified 
> Cs and / or Rb flying on those birds and no indication that the ground 
> segment is controlling such a payload. If all that *was* present, then 
> including them in the normal navigation solutions would be a "zero cost" next 
> step. 

Addressing the last sentence I found a government WAAS reference
which indicates that the WAAS satellites are indeed interchangeable
with GPS satellites in navigation solutions.  It is is on page 7 of
this

http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf

where it says

The WAAS GEO broadcast also provides an additional ranging source
for improved availability of navigation services. When a WAAS receiver
is using the corrections and integrity messages broadcast by the GEO,
only four GPS or GEO satellites are needed, which increases the
availability of service versus RAIM or RAIM/FDE.

While what is or isn't required in the satellite to support this is
still a mystery it seems like the timing accuracy coming back must
end up being equivalent to a real GPS satellite.  What this is good
for is interesting to think about.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Magnus Danielson]

On 07/05/2013 10:39 PM, Joseph Gwinn wrote:

Re: time-nuts Digest, Vol 108, Issue 28
Message: 2
Date: Fri, 05 Jul 2013 09:18:39 -0700
From: Jim Lux
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops
Message-ID:<51d6f1df.9090...@earthlink.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 7/5/13 8:44 AM, Bob Stewart wrote:

Wouldn't a Cs or Rb clock in orbit be slow due to relativistic
effects?  I'm pretty sure there is a relativistic correction to the
GPS clocks.

Bob - AE6RV




I believe that the original WAAS repurposed transponders intended for
other L-band satellite signals (e.g. Sirius/XM/LightSquared).

As noted earlier in the discussion, the new satellites might have a
specialized payload, which could have a purpose specific coherent
transponder, rather than a linear translator.

If it is purpose specific and single channel, then making it immune to
the local oscillator is straightforward.


I worked on a proposal for the original WAAS system.  The WAAS signal
is not a timing signal in the sense that GPS signals from space are
timing signals.  WAAS instead sends out a stream of correction data
that allows one to greatly improve the accuracy and reliability of GPS
signals.

So, unless things have changed greatly, the geostationary satellite
that broadcasts the WAAS signal need not have an atomic clock.


This is naturally still true, but we are into the level of "there's a 
signal here, what can we use it for?". Doing a much simplified receiver 
could serve some well enough, without going the full mounty. It's like 
taking the color-carrier of analog TV broadcasts.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops

[Joseph Gwinn]

> Re: time-nuts Digest, Vol 108, Issue 28
> Message: 2
> Date: Fri, 05 Jul 2013 09:18:39 -0700
> From: Jim Lux 
> To: time-nuts@febo.com
> Subject: Re: [time-nuts] Speaking of Costas loops
> Message-ID: <51d6f1df.9090...@earthlink.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 7/5/13 8:44 AM, Bob Stewart wrote:
>> Wouldn't a Cs or Rb clock in orbit be slow due to relativistic 
>> effects?  I'm pretty sure there is a relativistic correction to the 
>> GPS clocks.
>> 
>> Bob - AE6RV
>> 
>> 
> 
> I believe that the original WAAS repurposed transponders intended for 
> other L-band satellite signals (e.g. Sirius/XM/LightSquared).
> 
> As noted earlier in the discussion, the new satellites might have a 
> specialized payload, which could have a purpose specific coherent 
> transponder, rather than a linear translator.
> 
> If it is purpose specific and single channel, then making it immune to 
> the local oscillator is straightforward.

I worked on a proposal for the original WAAS system.  The WAAS signal 
is not a timing signal in the sense that GPS signals from space are 
timing signals.  WAAS instead sends out a stream of correction data 
that allows one to greatly improve the accuracy and reliability of GPS 
signals.  

So, unless things have changed greatly, the geostationary satellite 
that broadcasts the WAAS signal need not have an atomic clock.

Joe Gwinn
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Re: [time-nuts] Speaking of Costas loops

[Attila Kinali]

On Fri, 5 Jul 2013 12:14:20 -0400
Bob Camp  wrote:

> Indeed the atomic clocks on sats are set up so they can "tune" far
> enough to take out the relativistic effects. That (and a bunch of other
> things) makes them somewhat more expensive than their ground based cousins
> (like by 10-100X).

Something being space qualified already makes it 10-100 times more expensive.
A "simple" FET costs easily 100USD, 1000USD is not unheard of.


Attila Kinali

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
-- unknown
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Re: [time-nuts] Speaking of Costas loops

[Dennis Ferguson]

On 5 Jul, 2013, at 09:18 , Jim Lux  wrote:
> I believe that the original WAAS repurposed transponders intended for other 
> L-band satellite signals (e.g. Sirius/XM/LightSquared).

I'm not sure.  The original WAAS satellites, I think these

http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1996-070A
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1997-027A

indeed were commercial L-band satellites, as you suggest, but they still
note that

   Each INMARSAT-3 also carried a navigation transponder designed to
   enhance the accuracy, availability and integrity of the GPS and
   Glonass satellite navigation systems.

which leaves the impression that particular bit of hardware might be
special-purpose.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/5/13 8:44 AM, Bob Stewart wrote:

Wouldn't a Cs or Rb clock in orbit be slow due to relativistic effects?  I'm 
pretty sure there is a relativistic correction to the GPS clocks.

Bob - AE6RV




I believe that the original WAAS repurposed transponders intended for 
other L-band satellite signals (e.g. Sirius/XM/LightSquared).


As noted earlier in the discussion, the new satellites might have a 
specialized payload, which could have a purpose specific coherent 
transponder, rather than a linear translator.


If it is purpose specific and single channel, then making it immune to 
the local oscillator is straightforward.

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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

Indeed the atomic clocks on sats are set up so they can "tune" far enough to 
take out the relativistic effects. That (and a bunch of other things) makes 
them somewhat more expensive than their ground based cousins (like by 10-100X). 
They also have volume / power / cooling / reliability / weight issues (in 
addition to cost) that drive you to only use them if you really need to. The 
default option is to use some form of quartz. 

Bob

On Jul 5, 2013, at 11:44 AM, Bob Stewart  wrote:

> Wouldn't a Cs or Rb clock in orbit be slow due to relativistic effects?  I'm 
> pretty sure there is a relativistic correction to the GPS clocks.
> 
> Bob - AE6RV
> 
> 
> 
> - Original Message -
>> From: Bob Camp 
>> To: Discussion of precise time and frequency measurement 
>> Cc: 
>> Sent: Friday, July 5, 2013 10:33 AM
>> Subject: Re: [time-nuts] Speaking of Costas loops
>> 
>> Hi
>> 
>> The sat needs to transmit at the GPS frequencies and have an uplink that 
>> works 
>> exclusively with those frequencies. (or at least that sub band). A 
>> "normal" transponder probably would not radiate at the GPS allocation, 
>> simply to be a good citizen. I believe the "specialization" is simply 
>> a frequency mod to allow WAAS to pass through. There is no mention of a 
>> space 
>> qualified Cs and / or Rb flying on those birds and no indication that the 
>> ground 
>> segment is controlling such a payload. If all that *was* present, then 
>> including 
>> them in the normal navigation solutions would be a "zero cost" next 
>> step. 
>> 
>> Bob
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Re: [time-nuts] Speaking of Costas loops

[Bob Stewart]

Wouldn't a Cs or Rb clock in orbit be slow due to relativistic effects?  I'm 
pretty sure there is a relativistic correction to the GPS clocks.

Bob - AE6RV



- Original Message -
> From: Bob Camp 
> To: Discussion of precise time and frequency measurement 
> Cc: 
> Sent: Friday, July 5, 2013 10:33 AM
> Subject: Re: [time-nuts] Speaking of Costas loops
> 
> Hi
> 
> The sat needs to transmit at the GPS frequencies and have an uplink that 
> works 
> exclusively with those frequencies. (or at least that sub band). A 
> "normal" transponder probably would not radiate at the GPS allocation, 
> simply to be a good citizen. I believe the "specialization" is simply 
> a frequency mod to allow WAAS to pass through. There is no mention of a space 
> qualified Cs and / or Rb flying on those birds and no indication that the 
> ground 
> segment is controlling such a payload. If all that *was* present, then 
> including 
> them in the normal navigation solutions would be a "zero cost" next 
> step. 
> 
> Bob
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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

The sat needs to transmit at the GPS frequencies and have an uplink that works 
exclusively with those frequencies. (or at least that sub band). A "normal" 
transponder probably would not radiate at the GPS allocation, simply to be a 
good citizen. I believe the "specialization" is simply a frequency mod to allow 
WAAS to pass through. There is no mention of a space qualified Cs and / or Rb 
flying on those birds and no indication that the ground segment is controlling 
such a payload. If all that *was* present, then including them in the normal 
navigation solutions would be a "zero cost" next step. 

Bob

On Jul 4, 2013, at 11:16 PM, Dennis Ferguson  
wrote:

> 
> On 3 Jul, 2013, at 21:05 , Bob Camp  wrote:
>> If the WAAS sats were purpose designed to provide a high accuracy carrier, 
>> then yes there are ways to do it. The fundamental design concept of a "bent 
>> pipe" is that you don't do any of that. You do not care what's going through 
>> the bird, it just maps the input frequencies to the output and amplifies 
>> them (a lot). Again, the WAAS signal is simply piggybacking on existing 
>> hardware. The conversion oscillator is not locked to the GPS carrier (or to 
>> any other carrier). It's simply a free running quartz based oscillator, 
>> running into a synthesizer to get the appropriate microwave frequency. 
> 
> I'm not sure about the "Again, ..." part.  All three WAAS satellites are 
> commercial
> satellites but they were all launched recently enough (2 in 2005, 1 in 2008) 
> to have
> had WAAS-specific payload added.  The solicitation for the 2008 satellite is 
> here
> 
>   
> 
> 
> and is dated 2002; this isn't looking for service on a satellite already in 
> orbit.  For
> the 2005 satellites, the Telesat one is mentioned here
> 
>   http://www.telesat.com/services/government-services
> 
> which says
> 
>Telesat’s Anik F1R includes a specialized payload for the Wide Area 
> Augmentation
>System
> 
> while you look at the Orbital Sciences blurb on the last three satellites it 
> built for
> PanAmSat, here
> 
>   http://www.orbital.com/newsinfo/publications/galaxy_fact.pdf
> 
> you'll see that they are all exclusively satellite TV things, with 24 active
> C-band transponders and 8 spares, except for Galaxy 15 which weighs 350 pounds
> more than the other two and about which it says:
> 
>The Galaxy 15 satellite, which features a unique hybrid payload
>configuration, was launched on October 13, 2005. In addition to C-band
>commercial communications, the spacecraft also broadcasts Global
>Positioning System (GPS) navigation data using L-band frequencies as
>part of the Geostationary Communications and Control Segment (GCCS)
>implemented by Lockheed Martin for the U.S. Federal Aviation
>Administration (FAA).
> 
> I don't think they can use any old satellite for WAAS, they added payload
> for it.  Note that when Galaxy 15 went awol it took the WAAS service with it
> for most of a year even though it was replaced in its orbital slot for TV 
> service
> by a spare within a week or so (though Wikipedia says the replacement was 
> Galaxy 12
> so I guess that's predictable from the blurb above).
> 
> So I've been assuming that while the WAAS satellites are commercial the WAAS
> transmitters are specialized to the service and included for its exclusive 
> use.
> I hence guess they could have been designed to work however they needed to.
> 
> Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Dennis Ferguson]

On 3 Jul, 2013, at 21:05 , Bob Camp  wrote:
> If the WAAS sats were purpose designed to provide a high accuracy carrier, 
> then yes there are ways to do it. The fundamental design concept of a "bent 
> pipe" is that you don't do any of that. You do not care what's going through 
> the bird, it just maps the input frequencies to the output and amplifies them 
> (a lot). Again, the WAAS signal is simply piggybacking on existing hardware. 
> The conversion oscillator is not locked to the GPS carrier (or to any other 
> carrier). It's simply a free running quartz based oscillator, running into a 
> synthesizer to get the appropriate microwave frequency. 

I'm not sure about the "Again, ..." part.  All three WAAS satellites are 
commercial
satellites but they were all launched recently enough (2 in 2005, 1 in 2008) to 
have
had WAAS-specific payload added.  The solicitation for the 2008 satellite is 
here

   


and is dated 2002; this isn't looking for service on a satellite already in 
orbit.  For
the 2005 satellites, the Telesat one is mentioned here

   http://www.telesat.com/services/government-services

which says

Telesat’s Anik F1R includes a specialized payload for the Wide Area 
Augmentation
System

while you look at the Orbital Sciences blurb on the last three satellites it 
built for
PanAmSat, here

   http://www.orbital.com/newsinfo/publications/galaxy_fact.pdf

you'll see that they are all exclusively satellite TV things, with 24 active
C-band transponders and 8 spares, except for Galaxy 15 which weighs 350 pounds
more than the other two and about which it says:

The Galaxy 15 satellite, which features a unique hybrid payload
configuration, was launched on October 13, 2005. In addition to C-band
commercial communications, the spacecraft also broadcasts Global
Positioning System (GPS) navigation data using L-band frequencies as
part of the Geostationary Communications and Control Segment (GCCS)
implemented by Lockheed Martin for the U.S. Federal Aviation
Administration (FAA).

I don't think they can use any old satellite for WAAS, they added payload
for it.  Note that when Galaxy 15 went awol it took the WAAS service with it
for most of a year even though it was replaced in its orbital slot for TV 
service
by a spare within a week or so (though Wikipedia says the replacement was 
Galaxy 12
so I guess that's predictable from the blurb above).

So I've been assuming that while the WAAS satellites are commercial the WAAS
transmitters are specialized to the service and included for its exclusive use.
I hence guess they could have been designed to work however they needed to.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

I believe the *code* is corrected, but the carrier frequency is not. Without 
correction it's plenty close enough for any receiver that can handle a normal 
GPS sat. The intended "product" is the code rather than the carrier. Even if 
you tried to correct for doppler, it would only work for a single point. Your 
velocity to every place else would be either to fast or to slow for the 
correction (the motion is in 3 dimensions …).

Bob

On Jul 4, 2013, at 5:23 PM, Magnus Danielson  wrote:

> On 07/03/2013 02:29 PM, Bob Camp wrote:
>> Hi
>> 
>> There are two batches of GPS / WAAS sats up there:
>> 
>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>> 
>> 2) The ones with numbers<= 32 that do nav. These are not geosync.
>> 
>> I believe the only ones with corrected / high stab clocks on board are those 
>> in the second group. The stuff in the first group aren't dedicated sats, 
>> just leased transponders on conventional multipurpose geosync birds.
> 
> Correct. But the up-link station monitors the signal and makes corrects as I 
> recall it. In fact, there is a whole array of monitoring stations to provide 
> for ionospheric corrections.
> 
> The orbit is also known and corrected for.
> 
> WAAS/EGNOS has 100 baud data, using half-rate convolution code.
> 
> Cheers,
> Magnus
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Re: [time-nuts] Speaking of Costas loops

[Magnus Danielson]

On 07/03/2013 02:29 PM, Bob Camp wrote:

Hi

There are two batches of GPS / WAAS sats up there:

1) The ones with numbers above 100 that are geosync and that only do WAAS

2) The ones with numbers<= 32 that do nav. These are not geosync.

I believe the only ones with corrected / high stab clocks on board are those in 
the second group. The stuff in the first group aren't dedicated sats, just 
leased transponders on conventional multipurpose geosync birds.


Correct. But the up-link station monitors the signal and makes corrects 
as I recall it. In fact, there is a whole array of monitoring stations 
to provide for ionospheric corrections.


The orbit is also known and corrected for.

WAAS/EGNOS has 100 baud data, using half-rate convolution code.

Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops

[Magnus Danielson]

On 07/03/2013 11:59 AM, Attila Kinali wrote:

On Tue, 2 Jul 2013 17:06:47 -0400
  wrote:


Valid concerns all. What I am building is a squaring circuit for
recovering the carrier from a WAAS GPS satellite. Granted there
is still some Doppler and other issues, but the accuracy would not
be bad and it just looks like a fun thing to do. Plus, I can use my
four foot diameter dish antenna to reduce the number of satellites seen,
reduce thermal ground noise, and get some signal gain.


Right.. i didnt think about the WAAS/EGNOS satelites.
If i'm not mistaken, then you dont have to correct for doppler, as
the satelites are stationary relative to you. The only thing you might
want to correct for are atmospheric changes, but if you are tracking
frequency only, and don't care about the phase relation, respektively
can live with some phase noise, then you dont even need to do that.

Correcting for atmospheric changes should be "fairly" simple. You just
need to decode the WAAS/EGNOS signal, read the atmosphere/TEC data out
and apply a phase shift according to that.


You still have doppler on WAAS/EGNOS since the orbit isn't really 
perfect, but it is less than for normal GPS birds.


You would need a pretty good directivity such that not nearby WAAS/EGNOS 
polutes the squaring. Using code (pretty simple) would allow to surpress 
nearby birds for cleaner result.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/4/13 7:33 AM, Didier Juges wrote:

That works well for transponders with o LY one signal. On commercial 
satellites, each transponder is shared among multiple signals, so that would 
not work.




Ah, yes.. if it's a linear transponder/translator..

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Re: [time-nuts] Speaking of Costas loops

[Didier Juges]

That works well for transponders with o LY one signal. On commercial 
satellites, each transponder is shared among multiple signals, so that would 
not work.

Didier


Jim Lux  wrote:
>On 7/3/13 2:21 PM, Dennis Ferguson wrote:
>>
>> On 3 Jul, 2013, at 11:47 , Bob Camp  wrote:
>>> The pipe in this case is up on one frequency and down on another.
>The conversion oscillator on satellite that's the weak link, no matter
>how good the signal from the ground happens to be.
>>
>> That's certainly true but it doesn't seem like a problem that the
>> presence of a high stability free-running oscillator, like a
>rubidium,
>> would help.  The oscillator on a geostationary satellite has a
>> continuous frequency reference to lock to (the uplink carrier) and
>> hence only needs short term stability sufficient to track this and
>> transfer it accurately to the downlink.  It seems like this is the
>> kind of problem that quartz excels at.
>>
>
>Kind of depends on what the transponder on the satellite looks like.
>
>For deep space, we use a very narrow band loop filter to recover the 
>received carrier.  The synthesis approach for the downlink is designed 
>to cancel any variations in the local crystal oscillator (e.g. it's 
>typically a ratio.. for X band, 880/749)
>
>
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-- 
Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other 
things.
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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

The way doppler is corrected on a normal GPS is by having a large body of 
orbital data for each sat measured by a bunch of stations and then processed 
into the almanac. It's not a trivial process.

Since the doppler is in the hundred Hz or so range, I'd bet the conversion 
oscillator was designed to a similar spec. There may also be other issues as 
well. 

You would do *much* better for far less money simply using the same data 
collection process to do common view GPS with normal gear.

Bob

On Jul 4, 2013, at 3:06 AM, Hal Murray  wrote:

> 
> li...@rtty.us said:
>> If the WAAS sats were purpose designed to provide a high accuracy carrier,
>> then yes there are ways to do it. The fundamental design concept of a "bent
>> pipe" is that you don't do any of that. You do not care what's going through
>> the bird, it just maps the input frequencies to the output and amplifies
>> them (a lot). Again, the WAAS signal is simply piggybacking on existing
>> hardware. The conversion oscillator is not locked to the GPS carrier (or to
>> any other carrier). It's simply a free running quartz based oscillator,
>> running into a synthesizer to get the appropriate microwave frequency.  
> 
> If somebody wanted to use that path for a frequency reference, they could 
> setup a ground station to measure the Doppler and distribute that so people 
> could adjust their expectations.
> 
> I suspect measuring the Doppler is a common sanity check.
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Speaking of Costas loops

[Magnus Danielson]

Hi Ed,

On 07/02/2013 08:21 PM, ed breya wrote:

Here we go again - the first send didn't seem to get through. This is
the second attempt.

This talk of Costas loops reminded me of something I wanted to
investigate some day. I read somewhere a while back about carrier-phase
measurements, and various methods for recovering the GPS carrier
frequencies, including the Costas loop, and something with
carrier-squaring. Nothing I found showed actual examples or detail of
how this is done, only high-order mathematical descriptions.

For my needs, I'm more of a frequency-nut - I usually don't care about
getting time info, but I'd like perfect 10 MHz for reference. Can using
only the carriers lead to simple ways to get the same (or better)
frequency stability as a conventional GPSDO, but without the time and
location info, or is it pointless to worry about it, and just go with
full GPS decoding of everything? Or, is carrier-phase just an
enhancement only if you already have the full GPS info?

I know that the group could redesign the whole GPS system with tubes if
necessary, considering recent philosophical discussions on that, so I
think there's plenty of knowledge here about carrier-phase related stuff
too.


Just using the carrier phase in bare form isn't directly useful, as it 
will be shifted in frequency by the doppler, creating a 1,57542 GHz +/- 
6 kHz. If you decode the message (isn't all that much work) you get the 
nav messaeg, the detailed orbits and can correct using that, but once 
you got this far you could just as well do full nav message.


Cheers,
Magnus
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Re: [time-nuts] Speaking of Costas loops

[Hal Murray]

li...@rtty.us said:
> If the WAAS sats were purpose designed to provide a high accuracy carrier,
> then yes there are ways to do it. The fundamental design concept of a "bent
> pipe" is that you don't do any of that. You do not care what's going through
> the bird, it just maps the input frequencies to the output and amplifies
> them (a lot). Again, the WAAS signal is simply piggybacking on existing
> hardware. The conversion oscillator is not locked to the GPS carrier (or to
> any other carrier). It's simply a free running quartz based oscillator,
> running into a synthesizer to get the appropriate microwave frequency.  

If somebody wanted to use that path for a frequency reference, they could 
setup a ground station to measure the Doppler and distribute that so people 
could adjust their expectations.

I suspect measuring the Doppler is a common sanity check.



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/3/13 2:21 PM, Dennis Ferguson wrote:


On 3 Jul, 2013, at 11:47 , Bob Camp  wrote:

The pipe in this case is up on one frequency and down on another. The 
conversion oscillator on satellite that's the weak link, no matter how good the 
signal from the ground happens to be.


That's certainly true but it doesn't seem like a problem that the
presence of a high stability free-running oscillator, like a rubidium,
would help.  The oscillator on a geostationary satellite has a
continuous frequency reference to lock to (the uplink carrier) and
hence only needs short term stability sufficient to track this and
transfer it accurately to the downlink.  It seems like this is the
kind of problem that quartz excels at.



Kind of depends on what the transponder on the satellite looks like.

For deep space, we use a very narrow band loop filter to recover the 
received carrier.  The synthesis approach for the downlink is designed 
to cancel any variations in the local crystal oscillator (e.g. it's 
typically a ratio.. for X band, 880/749)



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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

On Jul 3, 2013, at 3:51 PM, jmfra...@cox.net wrote:

> http://www.navipedia.net/index.php/WAAS_Signal_Structure
> 
> Doppler Shift: The Doppler shift, as perceived by a stationary user, on the 
> signal broadcast by WAAS GEOs is less than 40 meters per second (≈210 Hz at 
> L1)

So unless you can measure and correct for the doppler, you are at a few hundred 
Hz at 1.5 GHz. 150 Hz would be 0.1 ppm. That's not very accurate. 

> in the worst case (at the end of life of the GEOs). The Doppler shift is due 
> to the relative motion of the GEO. 
> Carrier Frequency Stability: The short term stability of the carrier 
> frequency (square root of the Allan Variance) at the input of the user´s 
> receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding 
> the effects of the ionosphere and Doppler. 
> Polarization: The broadcast signal is right-handed circularly polarized. The 
> ellipticity will be no worse than 2 dB for the angular range of ±9.1o from 
> boresight. 
> Code/Carrier Frequency Coherence: The lack of coherence between the broadcast 
> carrier phase and the code phase shall be limited. The short term (<10sec) 
> fractional frequency difference between the code phase rate and the carrier 
> frequency shall be less than 5x10-11 (one sigma). Over the long term (<100 
> sec), the difference between the change in the broadcast code phase (convert 
> to carrier cycles) and the change in the broadcast carrier phase shall be 
> within one carrier cycle (one sigma). 

Once you are past 100 seconds, there's essentially no spec. One cycle per 100 
sec is a lot, even at 1.5 GHz

> Correlation Loss: Correlation loss is defined as the ratio of output powers 
> from a perfect correlator for two cases: 1) the actual receiver WAAS signal 
> correlated against a perfect unfiltered PN reference, or 2) a perfect 
> unfiltered PN signal normalized to the same total power as the WAAS signal in 
> case 1. The correlation loss resulting from modulation imperfections and 
> filtering inside the WAAS satellite payload is less than 1 dB. 

If you are only after the carrier, the code stuff pretty much does not matter.

Bob

> 
> John WA4WDL
> 
>  Bob Camp  wrote: 
>> Hi
>> 
>> The pipe in this case is up on one frequency and down on another. The 
>> conversion oscillator on satellite that's the weak link, no matter how good 
>> the signal from the ground happens to be. 
>> 
>> Bob
>> 
>> On Jul 3, 2013, at 1:48 PM, Attila Kinali  wrote:
>> 
>>> On Wed, 3 Jul 2013 08:29:02 -0400
>>> Bob Camp  wrote:
>>> 
 There are two batches of GPS / WAAS sats up there:
 
 1) The ones with numbers above 100 that are geosync and that only do WAAS
 
 2) The ones with numbers <= 32 that do nav. These are not geosync. 
 
 I believe the only ones with corrected / high stab clocks on board are
 those in the second group. The stuff in the first group aren't dedicated
 sats, just leased transponders on conventional multipurpose geosync birds. 
>>> 
>>> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
>>> ground using Cs references and retransmitted by the satelites using
>>> a "bend pipe". Ie. the signals should be of time-nut quality even without
>>> high accuracy frequency standards in the birds themselves.
>>> 
>>> (Sorry, i'm not able to find where i read about that, so no references 
>>> today)
>>> 
>>> Attila Kinali
>>> 
>>> -- 
>>> The people on 4chan are like brilliant psychologists
>>> who also happen to be insane and gross.
>>> -- unknown
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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>> 
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Re: [time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/3/13 12:42 PM, Azelio Boriani wrote:

Sure about the "bent pipe"? If so it seems that much power is required
at the transmitting ground station...


Much "equivalent" power is required.  If you have a 20 meter or so 
antenna, it doesn't take much to get a pretty  high EIRP.


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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

If the WAAS sats were purpose designed to provide a high accuracy carrier, then 
yes there are ways to do it. The fundamental design concept of a "bent pipe" is 
that you don't do any of that. You do not care what's going through the bird, 
it just maps the input frequencies to the output and amplifies them (a lot). 
Again, the WAAS signal is simply piggybacking on existing hardware. The 
conversion oscillator is not locked to the GPS carrier (or to any other 
carrier). It's simply a free running quartz based oscillator, running into a 
synthesizer to get the appropriate microwave frequency. 

Bob

On Jul 3, 2013, at 5:21 PM, Dennis Ferguson  wrote:

> 
> On 3 Jul, 2013, at 11:47 , Bob Camp  wrote:
>> The pipe in this case is up on one frequency and down on another. The 
>> conversion oscillator on satellite that's the weak link, no matter how good 
>> the signal from the ground happens to be. 
> 
> That's certainly true but it doesn't seem like a problem that the
> presence of a high stability free-running oscillator, like a rubidium,
> would help.  The oscillator on a geostationary satellite has a
> continuous frequency reference to lock to (the uplink carrier) and
> hence only needs short term stability sufficient to track this and
> transfer it accurately to the downlink.  It seems like this is the
> kind of problem that quartz excels at.
> 
> Dennis Ferguson
> 
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Re: [time-nuts] Speaking of Costas loops

[Dennis Ferguson]

On 3 Jul, 2013, at 11:47 , Bob Camp  wrote:
> The pipe in this case is up on one frequency and down on another. The 
> conversion oscillator on satellite that's the weak link, no matter how good 
> the signal from the ground happens to be. 

That's certainly true but it doesn't seem like a problem that the
presence of a high stability free-running oscillator, like a rubidium,
would help.  The oscillator on a geostationary satellite has a
continuous frequency reference to lock to (the uplink carrier) and
hence only needs short term stability sufficient to track this and
transfer it accurately to the downlink.  It seems like this is the
kind of problem that quartz excels at.

Dennis Ferguson

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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

The power at transmit is partially a function of making it tough for backyard 
"what ever nuts" to broadcast through the sats. Since there's no demodulation / 
decoding / encoding / remodulation, power is the only practical lockout 
mechanism. 

It's secondarily a function of the massive amount of random RF we generate all 
over the planet. They want signals that are "clean" to -60 dbc or better. They 
actually sell slots that are in the > -50 dbc range to people for specialized 
use. There is some modulation magic involved, so that's not quite the same as 
main transmit is 60 db >  sum of (everything else). 

http://en.wikipedia.org/wiki/Transponder_(satellite_communications)

Bob

On Jul 3, 2013, at 3:42 PM, Azelio Boriani  wrote:

> Sure about the "bent pipe"? If so it seems that much power is required
> at the transmitting ground station...
> 
> On Wed, Jul 3, 2013 at 7:48 PM, Attila Kinali  wrote:
>> On Wed, 3 Jul 2013 08:29:02 -0400
>> Bob Camp  wrote:
>> 
>>> There are two batches of GPS / WAAS sats up there:
>>> 
>>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>>> 
>>> 2) The ones with numbers <= 32 that do nav. These are not geosync.
>>> 
>>> I believe the only ones with corrected / high stab clocks on board are
>>> those in the second group. The stuff in the first group aren't dedicated
>>> sats, just leased transponders on conventional multipurpose geosync birds.
>> 
>> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
>> ground using Cs references and retransmitted by the satelites using
>> a "bend pipe". Ie. the signals should be of time-nut quality even without
>> high accuracy frequency standards in the birds themselves.
>> 
>> (Sorry, i'm not able to find where i read about that, so no references today)
>> 
>>Attila Kinali
>> 
>> --
>> The people on 4chan are like brilliant psychologists
>> who also happen to be insane and gross.
>>-- unknown
>> ___
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Re: [time-nuts] Speaking of Costas loops

[Dennis Ferguson]

On 3 Jul, 2013, at 10:48 , Attila Kinali  wrote:

> On Wed, 3 Jul 2013 08:29:02 -0400
> Bob Camp  wrote:
> 
>> There are two batches of GPS / WAAS sats up there:
>> 
>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>> 
>> 2) The ones with numbers <= 32 that do nav. These are not geosync. 
>> 
>> I believe the only ones with corrected / high stab clocks on board are
>> those in the second group. The stuff in the first group aren't dedicated
>> sats, just leased transponders on conventional multipurpose geosync birds. 
> 
> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> ground using Cs references and retransmitted by the satelites using
> a "bend pipe". Ie. the signals should be of time-nut quality even without
> high accuracy frequency standards in the birds themselves.
> 
> (Sorry, i'm not able to find where i read about that, so no references today)

I have also read that WAAS satellites can be usefully included in the GPS
solution, so they aren't necessarily inferior, but I also don't have
a reference.  There is this:

http://tf.boulder.nist.gov/general/pdf/2299.pdf

The clocks are indeed ground based and good quality.  The advantage of using
them as an alternative to GPS CV (which is what the paper is about) is that
they transmit unencrypted code on two frequencies to allow computing ionospheric
corrections and they don't move (much) so you can track them continuously with
a dish to get a big signal-to-noise improvement and multipath insensitivity.  
The
last bit seems like a mixed blessing, though, since the dish means you depend on
only the one satellite it is pointed at and hence suffer from whatever bad 
things
happen to it.  The paper notes events that it characterises as an "increasing 
problem
with the broadcast WAAS ephemeris", followed by an outage and clock jump, which 
I
interpret as maybe being an adjustment made to the satellite orbit which can't
be represented properly in the ephemeris.  I assume that could happen with 
regular GPS
satellites too, but if you are tracking a lot of them at once it is easy to 
detect
and toss out a solution outlier.

Dennis Ferguson
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Re: [time-nuts] Speaking of Costas loops

[Azelio Boriani]

Sure about the "bent pipe"? If so it seems that much power is required
at the transmitting ground station...

On Wed, Jul 3, 2013 at 7:48 PM, Attila Kinali  wrote:
> On Wed, 3 Jul 2013 08:29:02 -0400
> Bob Camp  wrote:
>
>> There are two batches of GPS / WAAS sats up there:
>>
>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>>
>> 2) The ones with numbers <= 32 that do nav. These are not geosync.
>>
>> I believe the only ones with corrected / high stab clocks on board are
>> those in the second group. The stuff in the first group aren't dedicated
>> sats, just leased transponders on conventional multipurpose geosync birds.
>
> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> ground using Cs references and retransmitted by the satelites using
> a "bend pipe". Ie. the signals should be of time-nut quality even without
> high accuracy frequency standards in the birds themselves.
>
> (Sorry, i'm not able to find where i read about that, so no references today)
>
> Attila Kinali
>
> --
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
> -- unknown
> ___
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Re: [time-nuts] Speaking of Costas loops

[jmfranke]

http://www.navipedia.net/index.php/WAAS_Signal_Structure

Doppler Shift: The Doppler shift, as perceived by a stationary user, on the 
signal broadcast by WAAS GEOs is less than 40 meters per second (≈210 Hz at L1) 
in the worst case (at the end of life of the GEOs). The Doppler shift is due to 
the relative motion of the GEO. 
Carrier Frequency Stability: The short term stability of the carrier frequency 
(square root of the Allan Variance) at the input of the user´s receiver antenna 
will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the 
ionosphere and Doppler. 
Polarization: The broadcast signal is right-handed circularly polarized. The 
ellipticity will be no worse than 2 dB for the angular range of ±9.1o from 
boresight. 
Code/Carrier Frequency Coherence: The lack of coherence between the broadcast 
carrier phase and the code phase shall be limited. The short term (<10sec) 
fractional frequency difference between the code phase rate and the carrier 
frequency shall be less than 5x10-11 (one sigma). Over the long term (<100 
sec), the difference between the change in the broadcast code phase (convert to 
carrier cycles) and the change in the broadcast carrier phase shall be within 
one carrier cycle (one sigma). 
Correlation Loss: Correlation loss is defined as the ratio of output powers 
from a perfect correlator for two cases: 1) the actual receiver WAAS signal 
correlated against a perfect unfiltered PN reference, or 2) a perfect 
unfiltered PN signal normalized to the same total power as the WAAS signal in 
case 1. The correlation loss resulting from modulation imperfections and 
filtering inside the WAAS satellite payload is less than 1 dB. 

John WA4WDL

 Bob Camp  wrote: 
> Hi
> 
> The pipe in this case is up on one frequency and down on another. The 
> conversion oscillator on satellite that's the weak link, no matter how good 
> the signal from the ground happens to be. 
> 
> Bob
> 
> On Jul 3, 2013, at 1:48 PM, Attila Kinali  wrote:
> 
> > On Wed, 3 Jul 2013 08:29:02 -0400
> > Bob Camp  wrote:
> > 
> >> There are two batches of GPS / WAAS sats up there:
> >> 
> >> 1) The ones with numbers above 100 that are geosync and that only do WAAS
> >> 
> >> 2) The ones with numbers <= 32 that do nav. These are not geosync. 
> >> 
> >> I believe the only ones with corrected / high stab clocks on board are
> >> those in the second group. The stuff in the first group aren't dedicated
> >> sats, just leased transponders on conventional multipurpose geosync birds. 
> > 
> > I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> > ground using Cs references and retransmitted by the satelites using
> > a "bend pipe". Ie. the signals should be of time-nut quality even without
> > high accuracy frequency standards in the birds themselves.
> > 
> > (Sorry, i'm not able to find where i read about that, so no references 
> > today)
> > 
> > Attila Kinali
> > 
> > -- 
> > The people on 4chan are like brilliant psychologists
> > who also happen to be insane and gross.
> > -- unknown
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to 
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> 
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Re: [time-nuts] Speaking of Costas loops

[bg]

Attila,

> On Wed, 3 Jul 2013 08:29:02 -0400
> Bob Camp  wrote:
>
>> There are two batches of GPS / WAAS sats up there:
>>
>> 1) The ones with numbers above 100 that are geosync and that only do
>> WAAS
>>
>> 2) The ones with numbers <= 32 that do nav. These are not geosync.
>>
>> I believe the only ones with corrected / high stab clocks on board are
>> those in the second group. The stuff in the first group aren't dedicated
>> sats, just leased transponders on conventional multipurpose geosync
>> birds.
>
> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> ground using Cs references and retransmitted by the satelites using
> a "bend pipe". Ie. the signals should be of time-nut quality even without
> high accuracy frequency standards in the birds themselves.
>
> (Sorry, i'm not able to find where i read about that, so no references
> today)
>
>   Attila Kinali

WAAS is the US implementation of SBAS, EGNOS the European, MSAS the
Japanese, GAGAN the Indian, etc...

Here are some references.

http://egnos-portal.gsa.europa.eu/library/technical-documents
http://egnos-portal.gsa.europa.eu/sites/default/files/content/documents/egnos-user-guide_en.pdf

You could also check the WAAS site at Stanford.edu.

--

Björn

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Re: [time-nuts] Speaking of Costas loops

[J. Forster]

A 'bent pipe' or retroreflector doubles any Dopplar from range rate.

-John





> On Wed, 3 Jul 2013 08:29:02 -0400
> Bob Camp  wrote:
>
>> There are two batches of GPS / WAAS sats up there:
>>
>> 1) The ones with numbers above 100 that are geosync and that only do
>> WAAS
>>
>> 2) The ones with numbers <= 32 that do nav. These are not geosync.
>>
>> I believe the only ones with corrected / high stab clocks on board are
>> those in the second group. The stuff in the first group aren't dedicated
>> sats, just leased transponders on conventional multipurpose geosync
>> birds.
>
> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> ground using Cs references and retransmitted by the satelites using
> a "bend pipe". Ie. the signals should be of time-nut quality even without
> high accuracy frequency standards in the birds themselves.
>
> (Sorry, i'm not able to find where i read about that, so no references
> today)
>
>   Attila Kinali
>
> --
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
>   -- unknown
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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

The pipe in this case is up on one frequency and down on another. The 
conversion oscillator on satellite that's the weak link, no matter how good the 
signal from the ground happens to be. 

Bob

On Jul 3, 2013, at 1:48 PM, Attila Kinali  wrote:

> On Wed, 3 Jul 2013 08:29:02 -0400
> Bob Camp  wrote:
> 
>> There are two batches of GPS / WAAS sats up there:
>> 
>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>> 
>> 2) The ones with numbers <= 32 that do nav. These are not geosync. 
>> 
>> I believe the only ones with corrected / high stab clocks on board are
>> those in the second group. The stuff in the first group aren't dedicated
>> sats, just leased transponders on conventional multipurpose geosync birds. 
> 
> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
> ground using Cs references and retransmitted by the satelites using
> a "bend pipe". Ie. the signals should be of time-nut quality even without
> high accuracy frequency standards in the birds themselves.
> 
> (Sorry, i'm not able to find where i read about that, so no references today)
> 
>   Attila Kinali
> 
> -- 
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
>   -- unknown
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Re: [time-nuts] Speaking of Costas loops

[Attila Kinali]

On Wed, 3 Jul 2013 08:29:02 -0400
Bob Camp  wrote:

> There are two batches of GPS / WAAS sats up there:
> 
> 1) The ones with numbers above 100 that are geosync and that only do WAAS
> 
> 2) The ones with numbers <= 32 that do nav. These are not geosync. 
> 
> I believe the only ones with corrected / high stab clocks on board are
> those in the second group. The stuff in the first group aren't dedicated
> sats, just leased transponders on conventional multipurpose geosync birds. 

I don't know about WAAS, but AFAIK the EGNOS signals are generated on
ground using Cs references and retransmitted by the satelites using
a "bend pipe". Ie. the signals should be of time-nut quality even without
high accuracy frequency standards in the birds themselves.

(Sorry, i'm not able to find where i read about that, so no references today)

Attila Kinali

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
-- unknown
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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

There are two batches of GPS / WAAS sats up there:

1) The ones with numbers above 100 that are geosync and that only do WAAS

2) The ones with numbers <= 32 that do nav. These are not geosync. 

I believe the only ones with corrected / high stab clocks on board are those in 
the second group. The stuff in the first group aren't dedicated sats, just 
leased transponders on conventional multipurpose geosync birds. 

Bob


On Jul 2, 2013, at 5:06 PM, jmfra...@cox.net wrote:

> Valid concerns all. What I am building is a squaring circuit for recovering 
> the carrier from a WAAS GPS satellite. Granted there is still some Doppler 
> and other issues, but the accuracy would not be bad and it just looks like a 
> fun thing to do. Plus, I can use my four foot diameter dish antenna to reduce 
> the number of satellites seen, reduce thermal ground noise, and get some 
> signal gain.
> 
> John  WA4WDL
> 
>  "J. Forster"  wrote: 
>> More on your question:
>> 
>> I'm prettyt sure that just sticking up an antenna and hooking up a simple,
>> phase tracking receiver for GPS will yeild nothing useful, because there
>> are always several birds in view, so you will get a superposition of their
>> signals in the bandpass and each signal will be Dopplar shifted be a
>> different amount- a time-varying amount.
>> 
>> You have to use a complete GPS receiver that can unravel it all.
>> 
>> -John
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>> Here we go again - the first send didn't seem to get through. This is
>>> the second attempt.
>>> 
>>> This talk of Costas loops reminded me of something I wanted to
>>> investigate some day. I read somewhere a while back about
>>> carrier-phase measurements, and various methods for recovering the
>>> GPS carrier frequencies, including the Costas loop, and something
>>> with carrier-squaring. Nothing I found showed actual examples or
>>> detail of how this is done, only high-order mathematical descriptions.
>>> 
>>> For my needs, I'm more of a frequency-nut - I usually don't care
>>> about getting time info, but I'd like perfect 10 MHz for reference.
>>> Can using only the carriers lead to simple ways to get the same (or
>>> better) frequency stability as a conventional GPSDO, but without the
>>> time and location info, or is it pointless to worry about it, and
>>> just go with full GPS decoding of everything? Or, is carrier-phase
>>> just an enhancement only if you already have the full GPS info?
>>> 
>>> I know that the group could redesign the whole GPS system with tubes
>>> if necessary, considering recent philosophical discussions on that,
>>> so I think there's plenty of knowledge here about carrier-phase
>>> related stuff too.
>>> 
>>> Ed
>>> 
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> 
>>> 
>> 
>> 
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Re: [time-nuts] Speaking of Costas loops

[Attila Kinali]

On Tue, 2 Jul 2013 17:06:47 -0400
 wrote:

> Valid concerns all. What I am building is a squaring circuit for
> recovering the carrier from a WAAS GPS satellite. Granted there
> is still some Doppler and other issues, but the accuracy would not
> be bad and it just looks like a fun thing to do. Plus, I can use my
> four foot diameter dish antenna to reduce the number of satellites seen,
> reduce thermal ground noise, and get some signal gain.

Right.. i didnt think about the WAAS/EGNOS satelites.
If i'm not mistaken, then you dont have to correct for doppler, as
the satelites are stationary relative to you. The only thing you might
want to correct for are atmospheric changes, but if you are tracking
frequency only, and don't care about the phase relation, respektively
can live with some phase noise, then you dont even need to do that.

Correcting for atmospheric changes should be "fairly" simple. You just
need to decode the WAAS/EGNOS signal, read the atmosphere/TEC data out
and apply a phase shift according to that.

Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
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Re: [time-nuts] Speaking of Costas loops

[paul swed]

Ed nothing attached


On Tue, Jul 2, 2013 at 2:05 PM, ed breya  wrote:

> This talk of Costas loops reminded me of something I wanted to investigate
> some day. I read somewhere a while back about carrier-phase measurements,
> and various methods for recovering the GPS carrier frequencies, including
> the Costas loop, and something with carrier-squaring. Nothing I found
> showed actual examples or detail of how this is done, only high-order
> mathematical descriptions.
>
> For my needs, I'm more of a frequency-nut - I usually don't care about
> getting time info, but I'd like perfect 10 MHz for reference. Can using
> only the carriers lead to simple ways to get the same (or better) frequency
> stability as a conventional GPSDO, but without the time and location info,
> or is it pointless to worry about it, and just go with full GPS decoding of
> everything? Or, is carrier-phase just an enhancement only if you already
> have the full GPS info?
>
> I know that the group could redesign the whole GPS system with tubes if
> necessary, considering recent philosophical discussions on that, so I think
> there's plenty of knowledge here about carrier-phase related stuff too.
>
> Ed
>
> __**_
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/**
> mailman/listinfo/time-nuts
> and follow the instructions there.
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Re: [time-nuts] Speaking of Costas loops

[jmfranke]

Valid concerns all. What I am building is a squaring circuit for recovering the 
carrier from a WAAS GPS satellite. Granted there is still some Doppler and 
other issues, but the accuracy would not be bad and it just looks like a fun 
thing to do. Plus, I can use my four foot diameter dish antenna to reduce the 
number of satellites seen, reduce thermal ground noise, and get some signal 
gain.

John  WA4WDL

 "J. Forster"  wrote: 
> More on your question:
> 
> I'm prettyt sure that just sticking up an antenna and hooking up a simple,
> phase tracking receiver for GPS will yeild nothing useful, because there
> are always several birds in view, so you will get a superposition of their
> signals in the bandpass and each signal will be Dopplar shifted be a
> different amount- a time-varying amount.
> 
> You have to use a complete GPS receiver that can unravel it all.
> 
> -John
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> > Here we go again - the first send didn't seem to get through. This is
> > the second attempt.
> >
> > This talk of Costas loops reminded me of something I wanted to
> > investigate some day. I read somewhere a while back about
> > carrier-phase measurements, and various methods for recovering the
> > GPS carrier frequencies, including the Costas loop, and something
> > with carrier-squaring. Nothing I found showed actual examples or
> > detail of how this is done, only high-order mathematical descriptions.
> >
> > For my needs, I'm more of a frequency-nut - I usually don't care
> > about getting time info, but I'd like perfect 10 MHz for reference.
> > Can using only the carriers lead to simple ways to get the same (or
> > better) frequency stability as a conventional GPSDO, but without the
> > time and location info, or is it pointless to worry about it, and
> > just go with full GPS decoding of everything? Or, is carrier-phase
> > just an enhancement only if you already have the full GPS info?
> >
> > I know that the group could redesign the whole GPS system with tubes
> > if necessary, considering recent philosophical discussions on that,
> > so I think there's plenty of knowledge here about carrier-phase
> > related stuff too.
> >
> > Ed
> >
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> >
> 
> 
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[time-nuts] Speaking of Costas loops

[ed breya]

This talk of Costas loops reminded me of something I wanted to 
investigate some day. I read somewhere a while back about 
carrier-phase measurements, and various methods for recovering the 
GPS carrier frequencies, including the Costas loop, and something 
with carrier-squaring. Nothing I found showed actual examples or 
detail of how this is done, only high-order mathematical descriptions.


For my needs, I'm more of a frequency-nut - I usually don't care 
about getting time info, but I'd like perfect 10 MHz for reference. 
Can using only the carriers lead to simple ways to get the same (or 
better) frequency stability as a conventional GPSDO, but without the 
time and location info, or is it pointless to worry about it, and 
just go with full GPS decoding of everything? Or, is carrier-phase 
just an enhancement only if you already have the full GPS info?


I know that the group could redesign the whole GPS system with tubes 
if necessary, considering recent philosophical discussions on that, 
so I think there's plenty of knowledge here about carrier-phase 
related stuff too.


Ed

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Re: [time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

Ok, cook book style:

Take the carrier, amplify it up, drive an agc to keep it up.
Drive the carrier into a full wave bridge rectifier made with low barrier diodes
Take the rectified output and feed it into a bandpass filter at 2X the carrier
The output is the squared carrier

There are at least a half dozen other ways to do the squaring.

Bob

On Jul 2, 2013, at 2:21 PM, ed breya  wrote:

> Here we go again - the first send didn't seem to get through. This is the 
> second attempt.
> 
> This talk of Costas loops reminded me of something I wanted to investigate 
> some day. I read somewhere a while back about carrier-phase measurements, and 
> various methods for recovering the GPS carrier frequencies, including the 
> Costas loop, and something with carrier-squaring. Nothing I found showed 
> actual examples or detail of how this is done, only high-order mathematical 
> descriptions.
> 
> For my needs, I'm more of a frequency-nut - I usually don't care about 
> getting time info, but I'd like perfect 10 MHz for reference. Can using only 
> the carriers lead to simple ways to get the same (or better) frequency 
> stability as a conventional GPSDO, but without the time and location info, or 
> is it pointless to worry about it, and just go with full GPS decoding of 
> everything? Or, is carrier-phase just an enhancement only if you already have 
> the full GPS info?
> 
> I know that the group could redesign the whole GPS system with tubes if 
> necessary, considering recent philosophical discussions on that, so I think 
> there's plenty of knowledge here about carrier-phase related stuff too.
> 
> Ed
> 
> ___
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Re: [time-nuts] Speaking of Costas loops

[Attila Kinali]

On Tue, 02 Jul 2013 11:21:24 -0700
ed breya  wrote:

> For my needs, I'm more of a frequency-nut - I usually don't care 
> about getting time info, but I'd like perfect 10 MHz for reference. 
> Can using only the carriers lead to simple ways to get the same (or 
> better) frequency stability as a conventional GPSDO, but without the 
> time and location info, or is it pointless to worry about it, and 
> just go with full GPS decoding of everything? Or, is carrier-phase 
> just an enhancement only if you already have the full GPS info?

The GPS carrier varies IIRC +/-6kHz (=+/-4ppm) due to doppler shift for a
stationary GPS receiver. Ie you need at least the satelites relative velocity
to correct for that, which in turn means you need to know where you are
relative to the satelite and where the satelite is heading. And to get that
you need the full solution for x/y/z/t and the almanach data.

After you have that, you can use carrier phase tracking to further improve
the accuracy (or is it the precision?) of your solution. I know i have
seen papers discussing that, but i cannot recall which they were.
I guess a couple of google queries should get you enough to read on that.

An interesting idea is to use long integration times (up to 100s) of the
GPS signal to get a better SNR and thus higher accuracy. But this in turn
needs that the refrence oscillator has a stability comparable to the Rb
reference on board of the GPS up to the integration time (if i have
understood the discussion in [1] and [2] correctly).

On the other hand, i know a guy who does sub-cm positioning with unmodified
LEA6-T, by logging their satelite phase data and heavy post processing over
hours of data and comparing it to a neaby basline of two stations with
known coordinates [3]. They are currently aiming at sub-mm resolution.

And just in case: Averaging the doppler shift out does not work out because
the distribution of the satelites and their velocity vectors has a non
zero mean for most locations on earth.

Attila Kinali


[1] "Effect of oscillator instability on GNSS signal integration time",
by Gaggero, 2008 (Master Thesis)
http://plan.geomatics.ucalgary.ca/papers/msc_thesis_gaggero_feb08.pdf

[2] "Ultra-stable Oscillators: Limits of GNSS Coherent Integration",
by Gaggero, Borio, 2008
http://plan.geomatics.ucalgary.ca/papers/ion08_ultrastable_pascalg_26sep08.pdf

[3] "GPS-Equipped Wireless Sensor Network Node for High-Accuracy Positioning
Applications", by Buchli, Sutton, Beutel, 2012
http://www.tik.ee.ethz.ch/~bbuchli/pubs/BSB2012_published.pdf

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
-- unknown
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Re: [time-nuts] Speaking of Costas loops

[J. Forster]

More on your question:

I'm prettyt sure that just sticking up an antenna and hooking up a simple,
phase tracking receiver for GPS will yeild nothing useful, because there
are always several birds in view, so you will get a superposition of their
signals in the bandpass and each signal will be Dopplar shifted be a
different amount- a time-varying amount.

You have to use a complete GPS receiver that can unravel it all.

-John










> Here we go again - the first send didn't seem to get through. This is
> the second attempt.
>
> This talk of Costas loops reminded me of something I wanted to
> investigate some day. I read somewhere a while back about
> carrier-phase measurements, and various methods for recovering the
> GPS carrier frequencies, including the Costas loop, and something
> with carrier-squaring. Nothing I found showed actual examples or
> detail of how this is done, only high-order mathematical descriptions.
>
> For my needs, I'm more of a frequency-nut - I usually don't care
> about getting time info, but I'd like perfect 10 MHz for reference.
> Can using only the carriers lead to simple ways to get the same (or
> better) frequency stability as a conventional GPSDO, but without the
> time and location info, or is it pointless to worry about it, and
> just go with full GPS decoding of everything? Or, is carrier-phase
> just an enhancement only if you already have the full GPS info?
>
> I know that the group could redesign the whole GPS system with tubes
> if necessary, considering recent philosophical discussions on that,
> so I think there's plenty of knowledge here about carrier-phase
> related stuff too.
>
> Ed
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Speaking of Costas loops

[J. Forster]

There is a Wiki article on Costas Loops that includes block diagrams.
There are books about the loop filter design.

Signal squaring is simply the Trig identity:

Sin(A)**2 = 1/2*[1 - cos(2*A)]

which has a DC term and a double frequency term. Sine is symmetriv about
the 0 axis.

In practice, with low S/N the Costas Loop is probably better.

-John

==


> Here we go again - the first send didn't seem to get through. This is
> the second attempt.
>
> This talk of Costas loops reminded me of something I wanted to
> investigate some day. I read somewhere a while back about
> carrier-phase measurements, and various methods for recovering the
> GPS carrier frequencies, including the Costas loop, and something
> with carrier-squaring. Nothing I found showed actual examples or
> detail of how this is done, only high-order mathematical descriptions.
>
> For my needs, I'm more of a frequency-nut - I usually don't care
> about getting time info, but I'd like perfect 10 MHz for reference.
> Can using only the carriers lead to simple ways to get the same (or
> better) frequency stability as a conventional GPSDO, but without the
> time and location info, or is it pointless to worry about it, and
> just go with full GPS decoding of everything? Or, is carrier-phase
> just an enhancement only if you already have the full GPS info?
>
> I know that the group could redesign the whole GPS system with tubes
> if necessary, considering recent philosophical discussions on that,
> so I think there's plenty of knowledge here about carrier-phase
> related stuff too.
>
> Ed
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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>
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Re: [time-nuts] Speaking of Costas loops

[Bob Stewart]

Hi Ed,

Are you talking about using GPS satellites, which means you have to have an 
extremely accurate clock to know where they are to correct for doppler, or are 
you talking about WWV, which means you have to deal with multi-path, 
atmospheric doppler, fading, and propagation?

Bob - AE6RV




- Original Message -
> From: ed breya 
> To: time-nuts@febo.com
> Cc: 
> Sent: Tuesday, July 2, 2013 1:21 PM
> Subject: [time-nuts] Speaking of Costas loops
> 
> Here we go again - the first send didn't seem to get through. This is the 
> second attempt.
> 

> For my needs, I'm more of a frequency-nut - I usually don't care about 
> getting time info, but I'd like perfect 10 MHz for reference. Can using only 
> the carriers lead to simple ways to get the same (or better) frequency 
> stability 
> as a conventional GPSDO, but without the time and location info, or is it 
> pointless to worry about it, and just go with full GPS decoding of 
> everything? 
> Or, is carrier-phase just an enhancement only if you already have the full 
> GPS 
> info?
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Re: [time-nuts] Speaking of Costas loops

[paul swed]

My lazy answer is GPSDOs work fine. This being time-nuts though and you did
use the word perfect means this is the start of a long thread.
Me I am staying with the Tbolt and 3801. Good enough.
Regards
Paul.


On Tue, Jul 2, 2013 at 2:21 PM, ed breya  wrote:

> Here we go again - the first send didn't seem to get through. This is the
> second attempt.
>
> This talk of Costas loops reminded me of something I wanted to investigate
> some day. I read somewhere a while back about carrier-phase measurements,
> and various methods for recovering the GPS carrier frequencies, including
> the Costas loop, and something with carrier-squaring. Nothing I found
> showed actual examples or detail of how this is done, only high-order
> mathematical descriptions.
>
> For my needs, I'm more of a frequency-nut - I usually don't care about
> getting time info, but I'd like perfect 10 MHz for reference. Can using
> only the carriers lead to simple ways to get the same (or better) frequency
> stability as a conventional GPSDO, but without the time and location info,
> or is it pointless to worry about it, and just go with full GPS decoding of
> everything? Or, is carrier-phase just an enhancement only if you already
> have the full GPS info?
>
> I know that the group could redesign the whole GPS system with tubes if
> necessary, considering recent philosophical discussions on that, so I think
> there's plenty of knowledge here about carrier-phase related stuff too.
>
> Ed
>
> __**_
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/**
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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[time-nuts] Speaking of Costas loops

[ed breya]

Here we go again - the first send didn't seem to get through. This is 
the second attempt.


This talk of Costas loops reminded me of something I wanted to 
investigate some day. I read somewhere a while back about 
carrier-phase measurements, and various methods for recovering the 
GPS carrier frequencies, including the Costas loop, and something 
with carrier-squaring. Nothing I found showed actual examples or 
detail of how this is done, only high-order mathematical descriptions.


For my needs, I'm more of a frequency-nut - I usually don't care 
about getting time info, but I'd like perfect 10 MHz for reference. 
Can using only the carriers lead to simple ways to get the same (or 
better) frequency stability as a conventional GPSDO, but without the 
time and location info, or is it pointless to worry about it, and 
just go with full GPS decoding of everything? Or, is carrier-phase 
just an enhancement only if you already have the full GPS info?


I know that the group could redesign the whole GPS system with tubes 
if necessary, considering recent philosophical discussions on that, 
so I think there's plenty of knowledge here about carrier-phase 
related stuff too.


Ed

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