Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[jimlux]

On 12/22/16 5:06 PM, Scott Stobbe wrote:

The other interesting aspect, is that if the transceiver is mobile, even at
a lazy pedestrian walking speed of 1 m/s, the resulting Doppler shift is 3
E-9 deltaF.



I always visualize this as "how many wavelengths per second".. so if 
you're at 10 GHz, 3cm wavelength, 1 m/s is 33 Hz.



to 1 sig fig, 1 m/s = 2 mi/hr

if it's a radar (2 way path) the shift is doubled.

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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Scott Stobbe]

The other interesting aspect, is that if the transceiver is mobile, even at
a lazy pedestrian walking speed of 1 m/s, the resulting Doppler shift is 3
E-9 deltaF.

On Thu, Dec 22, 2016 at 4:36 PM, Bob Camp  wrote:

> Hi
>
> For close in phase noise (< 10 Hz) the 10 MHz still wins over the 100 MHz
> after multiplication.
>
> ADEV of the 10 MHz (with or without frequency scale) will be better on the
> higher Q resonator.
> That will always be the low frequency overtone rather than the VHF crystal.
>
> Indeed, a large blank 5 MHz would beat the 10 MHz. It’s a good bet that if
> a 2.5 MHz cold weld
> SC with a 30 mm blank diameter existed, it would beat either one of them
> (Q would be much higher).
> Given the cost of coming up with that part …. not going to happen.
>
> Bob
>
> > On Dec 22, 2016, at 3:26 PM, Scott Stobbe 
> wrote:
> >
> > Well for the same Q a competing oscillator will still take a 20 dB phase
> > noise increase for every frequency decade you scale up to. If Q*f is
> > approximately constant, you take another 20 dB hit in phase noise from
> > degraded Q, totaling 40 dB/decade. Compared to 20 dB/decade plus the
> noise
> > introduced by the phase detector and loop-filter of the PLL.
> > https://en.wikipedia.org/wiki/Leeson's_equation
> >
> > On Thu, Dec 22, 2016 at 10:53 AM, Attila Kinali 
> wrote:
> >
> >> On Wed, 21 Dec 2016 18:59:20 -0800
> >> Chris Albertson  wrote:
> >>
> >>> Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is
> to
> >>> drive a microwave, why not build a MUCH higher frequency GPSDO.Is
> the
> >>> reason that 10MHz crystals just happen to be very good and there are
> not
> >>> good 100MHz ovenized crystals?  Or for portable use could you not use
> the
> >>> 1PPS signal to discipline a microwave oscillator.
> >>
> >> Short answer:
> >> GPSDOs are mostly about high stability, not about low phase noise.
> >> The 10MHz just happend to be a good compromise on stability, phase noise
> >> and usefulnes.
> >>
> >> Long answer:
> >> A GPSDO has to exhibit good stability up to several 100 s to a few 1000
> s.
> >> This dictates that the OCXO used has to have as high long term stability
> >> as possible. To get there you need an as thick crystal lab as possible.
> >> The lower the frequency and the higher the overtone, the better.
> >> Quartz resonators exhibit a nearly constant Q*f, so in first order
> >> approximation, there is no point in choosing a higher frequency
> >> crystal, as the Q will then decrease and thus increase the phase noise
> >> would have been the same as the increased phase noise of a frequency
> >> multiplier. Of course, frequency multiplication is not exactly perfect
> and
> >> the Q*f is not 100% flat. There is a sweet spot where Q*f is maximal
> >> between
> >> 5MHz and 10MHz. For historical reasons, 10MHz has been deemed the more
> >> useful
> >> value and that's the reason we have a lot of 10MHz OCXO. If you go for
> high
> >> stability oscillators, you will see a lot 5MHz OCXOs being used (for the
> >> increased stability). Of course nobody says that these are the only
> >> frequencies that can be used. For example, for specialized use cases you
> >> will find GPSDOs with "odd" frequencies (like the 30.72MHz/61.44MHz used
> >> for LTE).
> >>
> >> As others have already commented, when using GPSDOs as a frequency
> >> reference
> >> for an GHz link, one would use some high frequency oscillator in the
> lower
> >> 100MHz range (using a BAW quartz) or somewhere between 500MHz and
> 1000MHz
> >> (using an SAW quartz) as a low phase noise reference and upconvert this.
> >> Yes, it is possible to discipline such an oscillator directly using GPS,
> >> but for the sake of stability (see above), design reuse and ease of
> >> building/testing, using an 10MHz input is generally the better solution.
> >> This allows to use any device that can produce an 10MHz signal, like
> >> e.g. an Rb vapor cell standard.
> >>
> >>
> >>Attila Kinali
> >>
> >> --
> >> It is upon moral qualities that a society is ultimately founded. All
> >> the prosperity and technological sophistication in the world is of no
> >> use without that foundation.
> >> -- Miss Matheson, The Diamond Age, Neil Stephenson
> >> ___
> >> 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.
> >>
> > ___
> > 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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> and 

Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Bob Camp]

Hi

For close in phase noise (< 10 Hz) the 10 MHz still wins over the 100 MHz after 
multiplication.

ADEV of the 10 MHz (with or without frequency scale) will be better on the 
higher Q resonator.
That will always be the low frequency overtone rather than the VHF crystal.

Indeed, a large blank 5 MHz would beat the 10 MHz. It’s a good bet that if a 
2.5 MHz cold weld 
SC with a 30 mm blank diameter existed, it would beat either one of them (Q 
would be much higher).
Given the cost of coming up with that part …. not going to happen. 

Bob

> On Dec 22, 2016, at 3:26 PM, Scott Stobbe  wrote:
> 
> Well for the same Q a competing oscillator will still take a 20 dB phase
> noise increase for every frequency decade you scale up to. If Q*f is
> approximately constant, you take another 20 dB hit in phase noise from
> degraded Q, totaling 40 dB/decade. Compared to 20 dB/decade plus the noise
> introduced by the phase detector and loop-filter of the PLL.
> https://en.wikipedia.org/wiki/Leeson's_equation
> 
> On Thu, Dec 22, 2016 at 10:53 AM, Attila Kinali  wrote:
> 
>> On Wed, 21 Dec 2016 18:59:20 -0800
>> Chris Albertson  wrote:
>> 
>>> Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is to
>>> drive a microwave, why not build a MUCH higher frequency GPSDO.Is the
>>> reason that 10MHz crystals just happen to be very good and there are not
>>> good 100MHz ovenized crystals?  Or for portable use could you not use the
>>> 1PPS signal to discipline a microwave oscillator.
>> 
>> Short answer:
>> GPSDOs are mostly about high stability, not about low phase noise.
>> The 10MHz just happend to be a good compromise on stability, phase noise
>> and usefulnes.
>> 
>> Long answer:
>> A GPSDO has to exhibit good stability up to several 100 s to a few 1000 s.
>> This dictates that the OCXO used has to have as high long term stability
>> as possible. To get there you need an as thick crystal lab as possible.
>> The lower the frequency and the higher the overtone, the better.
>> Quartz resonators exhibit a nearly constant Q*f, so in first order
>> approximation, there is no point in choosing a higher frequency
>> crystal, as the Q will then decrease and thus increase the phase noise
>> would have been the same as the increased phase noise of a frequency
>> multiplier. Of course, frequency multiplication is not exactly perfect and
>> the Q*f is not 100% flat. There is a sweet spot where Q*f is maximal
>> between
>> 5MHz and 10MHz. For historical reasons, 10MHz has been deemed the more
>> useful
>> value and that's the reason we have a lot of 10MHz OCXO. If you go for high
>> stability oscillators, you will see a lot 5MHz OCXOs being used (for the
>> increased stability). Of course nobody says that these are the only
>> frequencies that can be used. For example, for specialized use cases you
>> will find GPSDOs with "odd" frequencies (like the 30.72MHz/61.44MHz used
>> for LTE).
>> 
>> As others have already commented, when using GPSDOs as a frequency
>> reference
>> for an GHz link, one would use some high frequency oscillator in the lower
>> 100MHz range (using a BAW quartz) or somewhere between 500MHz and 1000MHz
>> (using an SAW quartz) as a low phase noise reference and upconvert this.
>> Yes, it is possible to discipline such an oscillator directly using GPS,
>> but for the sake of stability (see above), design reuse and ease of
>> building/testing, using an 10MHz input is generally the better solution.
>> This allows to use any device that can produce an 10MHz signal, like
>> e.g. an Rb vapor cell standard.
>> 
>> 
>>Attila Kinali
>> 
>> --
>> It is upon moral qualities that a society is ultimately founded. All
>> the prosperity and technological sophistication in the world is of no
>> use without that foundation.
>> -- Miss Matheson, The Diamond Age, Neil Stephenson
>> ___
>> 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] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Scott Stobbe]

Well for the same Q a competing oscillator will still take a 20 dB phase
noise increase for every frequency decade you scale up to. If Q*f is
approximately constant, you take another 20 dB hit in phase noise from
degraded Q, totaling 40 dB/decade. Compared to 20 dB/decade plus the noise
introduced by the phase detector and loop-filter of the PLL.
https://en.wikipedia.org/wiki/Leeson's_equation

On Thu, Dec 22, 2016 at 10:53 AM, Attila Kinali  wrote:

> On Wed, 21 Dec 2016 18:59:20 -0800
> Chris Albertson  wrote:
>
> > Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is to
> > drive a microwave, why not build a MUCH higher frequency GPSDO.Is the
> > reason that 10MHz crystals just happen to be very good and there are not
> > good 100MHz ovenized crystals?  Or for portable use could you not use the
> > 1PPS signal to discipline a microwave oscillator.
>
> Short answer:
> GPSDOs are mostly about high stability, not about low phase noise.
> The 10MHz just happend to be a good compromise on stability, phase noise
> and usefulnes.
>
> Long answer:
> A GPSDO has to exhibit good stability up to several 100 s to a few 1000 s.
> This dictates that the OCXO used has to have as high long term stability
> as possible. To get there you need an as thick crystal lab as possible.
> The lower the frequency and the higher the overtone, the better.
> Quartz resonators exhibit a nearly constant Q*f, so in first order
> approximation, there is no point in choosing a higher frequency
> crystal, as the Q will then decrease and thus increase the phase noise
> would have been the same as the increased phase noise of a frequency
> multiplier. Of course, frequency multiplication is not exactly perfect and
> the Q*f is not 100% flat. There is a sweet spot where Q*f is maximal
> between
> 5MHz and 10MHz. For historical reasons, 10MHz has been deemed the more
> useful
> value and that's the reason we have a lot of 10MHz OCXO. If you go for high
> stability oscillators, you will see a lot 5MHz OCXOs being used (for the
> increased stability). Of course nobody says that these are the only
> frequencies that can be used. For example, for specialized use cases you
> will find GPSDOs with "odd" frequencies (like the 30.72MHz/61.44MHz used
> for LTE).
>
> As others have already commented, when using GPSDOs as a frequency
> reference
> for an GHz link, one would use some high frequency oscillator in the lower
> 100MHz range (using a BAW quartz) or somewhere between 500MHz and 1000MHz
> (using an SAW quartz) as a low phase noise reference and upconvert this.
> Yes, it is possible to discipline such an oscillator directly using GPS,
> but for the sake of stability (see above), design reuse and ease of
> building/testing, using an 10MHz input is generally the better solution.
> This allows to use any device that can produce an 10MHz signal, like
> e.g. an Rb vapor cell standard.
>
>
> Attila Kinali
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
> ___
> 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] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Attila Kinali]

On Wed, 21 Dec 2016 18:59:20 -0800
Chris Albertson  wrote:

> Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is to
> drive a microwave, why not build a MUCH higher frequency GPSDO.Is the
> reason that 10MHz crystals just happen to be very good and there are not
> good 100MHz ovenized crystals?  Or for portable use could you not use the
> 1PPS signal to discipline a microwave oscillator.

Short answer:
GPSDOs are mostly about high stability, not about low phase noise.
The 10MHz just happend to be a good compromise on stability, phase noise
and usefulnes.

Long answer:
A GPSDO has to exhibit good stability up to several 100 s to a few 1000 s.
This dictates that the OCXO used has to have as high long term stability
as possible. To get there you need an as thick crystal lab as possible.
The lower the frequency and the higher the overtone, the better.
Quartz resonators exhibit a nearly constant Q*f, so in first order
approximation, there is no point in choosing a higher frequency
crystal, as the Q will then decrease and thus increase the phase noise
would have been the same as the increased phase noise of a frequency
multiplier. Of course, frequency multiplication is not exactly perfect and
the Q*f is not 100% flat. There is a sweet spot where Q*f is maximal between
5MHz and 10MHz. For historical reasons, 10MHz has been deemed the more useful
value and that's the reason we have a lot of 10MHz OCXO. If you go for high
stability oscillators, you will see a lot 5MHz OCXOs being used (for the
increased stability). Of course nobody says that these are the only
frequencies that can be used. For example, for specialized use cases you
will find GPSDOs with "odd" frequencies (like the 30.72MHz/61.44MHz used
for LTE). 

As others have already commented, when using GPSDOs as a frequency reference
for an GHz link, one would use some high frequency oscillator in the lower
100MHz range (using a BAW quartz) or somewhere between 500MHz and 1000MHz
(using an SAW quartz) as a low phase noise reference and upconvert this.
Yes, it is possible to discipline such an oscillator directly using GPS,
but for the sake of stability (see above), design reuse and ease of
building/testing, using an 10MHz input is generally the better solution.
This allows to use any device that can produce an 10MHz signal, like
e.g. an Rb vapor cell standard.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[jimlux]

On 12/21/16 9:08 PM, John Hawkinson wrote:

Chris Albertson  (and Bob Camp ):

Why to people always build 10MHz GPSDOs?


Because "a lot" (...) of amateur radio microwave equipment is designed
off the shelf to accept an external 10 MHz input. [And other kinds of
equipment, too.] If you're not designing from the ground-up, then it makes
a lot of sense.

-


In most cases, folks want good close in phase noise - 5 and 10 MHz are 
in the sweet spot of having good close in phase noise even after the 
20log(N) bump from multiplying it up.  A 100 MHz oscillator takes less 
multiplication, but because the crystal is physically smaller, it 
probably doesn't have phase noise that is lower than a 10 MHz multiplied up.


if you're multiplying up to 8 or 10 or 32 GHz, whether you start at 10 
or 100, it's still a lot of multiplying.  If you're using a PLL, the 
frequency gets divided down into the phase/frequency comparator, and 
dividing down from 10 is no different than dividing down from 100.
If you're doing chains of multipliers up, then starting a 10 gives you a 
bit more flexibility to design the multiplier chain in terms of where 
the various frequencies wind up, so as to avoid "inband" spurs later on.


Most ham radio designs tend to be mixes and matches of previous widgets. 
The whole transverter model, starting with 10 meters or 2 meters, and 
then mixing, converting, multiplying, etc. is great if you're trying to 
re-use stuff you already have, gradually adding bands, or trying to use 
30-40 year old surplus microwave gear.  It's not necessarily a good 
approach if you were starting from scratch and using modern components.



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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Mike Seguin]

On 12/21/2016 2:06 PM, Eric Haskell wrote:

I am microwave amateur radio operator. A friend was discussing using an

eBay purchased Trimble 57963-D for providing a 10 MHz reference.

As you stated, the time needed for position hold is significant. For my 
microwave gear that needs 10 MHz in the field, I use a Jackson Labs 
LTE-Lite.


http://www.jackson-labs.com/index.php/products/lte_lite

It can be run in "mobile" mode. I have used it to discipline gear I run 
up to 241 GHz. Most of the disciplined LO's are Axtal in the 100 MHz 
range. It also supports 'position/hold' mode for use in a fixed position 
such as at home in my shop.


There was a group buy a while back.

Frankly, absolute frequency accuracy is a bit less of an issue than it 
used to be because so many of us now use SDR's for panadapters on 
receive. We can "see" 48/96/192 kHz of bandwidth at once so if a signal 
is off a few kHz and moves a bit, no big deal.


If you are trying to do weak signal digital modes, that's another story.

Mike

--

73,
Mike, N1JEZ
"A closed mouth gathers no feet"
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Tom Curlee]

I used one of the Jupiter GPS receivers that has a 10 KHz output to control my 
10 GHz LO to discipline one of the common "brick" type of microwave 
oscillators.  These oscillators have an internal crystal oscillator (106.6 MHz  
for a 10.224 GHz LO) that is multiplied up to the needed microwave frequency.  
I divided the 106.5 MHz oscillator frequency down to 10 KHz that was then 
compared to the 10 KHz output from the Jupiter.  The control loop is very 
simple: a single op amp, a resistor, and a large capacitor.  The response time 
is extremely slow - 5 to 10 seconds or more.  All I wanted was to nudge the 
crystal oscillator onto frequency.  

>From a warm GPS start, the LO is within 1 to 2 HZ at 10.224 GHZ within 45 to 
>60 seconds from power on.
The hardest part was designing the divider circuit to get 10 KHz from the 106.6 
MHz oscillator.

Tom 

WB6UZZ


  From: Eric Haskell <eric_hask...@hotmail.com>
 To: Time Nuts <time-nuts@febo.com> 
 Sent: Wednesday, December 21, 2016 11:06 AM
 Subject: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio 
Microwave Operations
   
Hello Time Nuts,  I have been on the group and have promoted it to other folks 
for a while but this may be my first post here.

I am microwave amateur radio operator and I have question to pose relating to 
the use of GPSDO's with amateur radio for microwave communication.

First, the more generic question.  A friend was discussing using a eBay 
purchased Trimble 57963-D for providing a 10 MHz refrence for his portable 
microwave station  (primarly at 10GHz).  He wants a clean high stability 10 MHz 
refrence mainly to lock the station LO. First I think a GPSDO is overkill for 
this application and I am thinking that a good surplus ovenized crystal 
oscillator should get him to within a few Hz after warm up and a Rb could do 
better but may have short term stability that may degrade phase noise of the 
LO.  I am concerned that a GPSDO is not designed for portable operations.  
Moving it should probably force a new site  survey which may take a day or more 
 to complete before it goes into disciplining mode so you would loose any 
potential benefit of a GPSDO by moving around frequently.  If he wants to do 
this I think he should leave it connected at his home location for an extended 
time (several days at least), then when he want to go portable (roving), h
 e should
  disconnect the GPS antenna entirely to force the unit into holdover mode 
maintain continuous power with battery backup which should maintain the 
internal OCXO very close to the target frequence and allow the holdover 
algorithm to compensate for OCXO for aging and best it can.  I would guess that 
if he chooses to used the GPSDO with the antenna connected it would probably 
never exit the site survey mode and you would have the output default to the 
last known good DAC value when it was been disciplined so it would be operating 
as a OCXO only (although potentially starting from a very accurate starting 
point, if it had been in use at a fixed location for a good while) before going 
portable.  Is this a correct view of the situation?  Any recommendations?

I also know of a fellow who has developed some excellent open source Linux 
software to drive an Ettus Research USRP microwave SDR transceiver for amateur 
radio microwave applications.  His code also has features to calculate antenna 
baring and with other available code compensates for satellite Doppler shift 
and/or synchronize digital communication modes using the GPS coordinates and 
timing data.  He has a built in interface for a Trimble Thunderbolt for this 
purpose.  I think it also might be a better solution to use a OCXO for 10 MHz 
and a cheap USB GPS sensor for location?  Is there a cheep USB GPS that 
provides PPS?  Any recommendations?

I have seen simpler GPS controlled 10 MHz sources like the Miller design that 
divides down a 10 MHz ref and compares it to a 10 KHz output from a Jupiter T 
GPS to tweak the ref freq that may or may not be better suited to this 
application as it may add phase noise to the LO but would be more real time in 
it's GPS correction to the reference frequency.

Regards,


Norman Eric Haskell

KC4YOE

Keller, TX USA
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Dave Brown]

It has been done. One I recall is Louis Cupido's Reflock system. TAPR did a 
kit for it some years back. Fairly sure there are others.
But there are a number of readily available 'systems'  these days that take 
a 10 MHz reference input and generate a 'clean' low microwave reference 
frequency output that minimises the required multiplication. The ZLPLL and 
the VK3XDK Agile PLL V2 are just two I am aware of.

DaveB, NZ
ZL3FJ

- Original Message - 
From: "Chris Albertson" <albertson.ch...@gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Sent: Thursday, December 22, 2016 3:59 PM
Subject: Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur 
Radio Microwave Operations




Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is to
drive a microwave, why not build a MUCH higher frequency GPSDO.Is the
reason that 10MHz crystals just happen to be very good and there are not
good 100MHz ovenized crystals?  Or for portable use could you not use the
1PPS signal to discipline a microwave oscillator.

Scaling up 10MHz is going to make noise, so why not start way higher and 
do

less scaling

On Wed, Dec 21, 2016 at 11:06 AM, Eric Haskell <eric_hask...@hotmail.com>
wrote:


Hello Time Nuts,  I have been on the group and have promoted it to other
folks for a while but this may be my first post here.

I am microwave amateur radio operator and I have question to pose 
relating

to the use of GPSDO's with amateur radio for microwave communication.

First, the more generic question.  A friend was discussing using a eBay
purchased Trimble 57963-D for providing a 10 MHz refrence for his 
portable
microwave station  (primarly at 10GHz).  He wants a clean high stability 
10

MHz refrence mainly to lock the station LO. First I think a GPSDO is
overkill for this application and I am thinking that a good surplus
ovenized crystal oscillator should get him to within a few Hz after warm 
up
and a Rb could do better but may have short term stability that may 
degrade

phase noise of the LO.  I am concerned that a GPSDO is not designed for
portable operations.  Moving it should probably force a new site  survey
which may take a day or more  to complete before it goes into 
disciplining

mode so you would loose any potential benefit of a GPSDO by moving around
frequently.  If he wants to do this I think he should leave it connected 
at

his home location for an extended time (several days at least), then when
he want to go portable (roving), he should
  disconnect the GPS antenna entirely to force the unit into holdover 
mode

maintain continuous power with battery backup which should maintain the
internal OCXO very close to the target frequence and allow the holdover
algorithm to compensate for OCXO for aging and best it can.  I would 
guess

that if he chooses to used the GPSDO with the antenna connected it would
probably never exit the site survey mode and you would have the output
default to the last known good DAC value when it was been disciplined so 
it

would be operating as a OCXO only (although potentially starting from a
very accurate starting point, if it had been in use at a fixed location 
for

a good while) before going portable.  Is this a correct view of the
situation?  Any recommendations?

I also know of a fellow who has developed some excellent open source 
Linux

software to drive an Ettus Research USRP microwave SDR transceiver for
amateur radio microwave applications.  His code also has features to
calculate antenna baring and with other available code compensates for
satellite Doppler shift and/or synchronize digital communication modes
using the GPS coordinates and timing data.  He has a built in interface 
for
a Trimble Thunderbolt for this purpose.  I think it also might be a 
better
solution to use a OCXO for 10 MHz and a cheap USB GPS sensor for 
location?

Is there a cheep USB GPS that provides PPS?  Any recommendations?

I have seen simpler GPS controlled 10 MHz sources like the Miller design
that divides down a 10 MHz ref and compares it to a 10 KHz output from a
Jupiter T GPS to tweak the ref freq that may or may not be better suited 
to
this application as it may add phase noise to the LO but would be more 
real

time in it's GPS correction to the reference frequency.

Regards,


Norman Eric Haskell

KC4YOE

Keller, TX USA
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Redondo Beach, California
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[John Hawkinson]

Chris Albertson  (and Bob Camp ):
> Why to people always build 10MHz GPSDOs?

Because "a lot" (...) of amateur radio microwave equipment is designed
off the shelf to accept an external 10 MHz input. [And other kinds of
equipment, too.] If you're not designing from the ground-up, then it makes
a lot of sense.

--jh...@mit.edu
  John Hawkinson
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Chris Albertson]

Why to people always build 10MHz GPSDOs?   If the use of the GPSDO is to
drive a microwave, why not build a MUCH higher frequency GPSDO.Is the
reason that 10MHz crystals just happen to be very good and there are not
good 100MHz ovenized crystals?  Or for portable use could you not use the
1PPS signal to discipline a microwave oscillator.

Scaling up 10MHz is going to make noise, so why not start way higher and do
less scaling

On Wed, Dec 21, 2016 at 11:06 AM, Eric Haskell 
wrote:

> Hello Time Nuts,  I have been on the group and have promoted it to other
> folks for a while but this may be my first post here.
>
> I am microwave amateur radio operator and I have question to pose relating
> to the use of GPSDO's with amateur radio for microwave communication.
>
> First, the more generic question.  A friend was discussing using a eBay
> purchased Trimble 57963-D for providing a 10 MHz refrence for his portable
> microwave station  (primarly at 10GHz).  He wants a clean high stability 10
> MHz refrence mainly to lock the station LO. First I think a GPSDO is
> overkill for this application and I am thinking that a good surplus
> ovenized crystal oscillator should get him to within a few Hz after warm up
> and a Rb could do better but may have short term stability that may degrade
> phase noise of the LO.  I am concerned that a GPSDO is not designed for
> portable operations.  Moving it should probably force a new site  survey
> which may take a day or more  to complete before it goes into disciplining
> mode so you would loose any potential benefit of a GPSDO by moving around
> frequently.  If he wants to do this I think he should leave it connected at
> his home location for an extended time (several days at least), then when
> he want to go portable (roving), he should
>   disconnect the GPS antenna entirely to force the unit into holdover mode
> maintain continuous power with battery backup which should maintain the
> internal OCXO very close to the target frequence and allow the holdover
> algorithm to compensate for OCXO for aging and best it can.  I would guess
> that if he chooses to used the GPSDO with the antenna connected it would
> probably never exit the site survey mode and you would have the output
> default to the last known good DAC value when it was been disciplined so it
> would be operating as a OCXO only (although potentially starting from a
> very accurate starting point, if it had been in use at a fixed location for
> a good while) before going portable.  Is this a correct view of the
> situation?  Any recommendations?
>
> I also know of a fellow who has developed some excellent open source Linux
> software to drive an Ettus Research USRP microwave SDR transceiver for
> amateur radio microwave applications.  His code also has features to
> calculate antenna baring and with other available code compensates for
> satellite Doppler shift and/or synchronize digital communication modes
> using the GPS coordinates and timing data.  He has a built in interface for
> a Trimble Thunderbolt for this purpose.  I think it also might be a better
> solution to use a OCXO for 10 MHz and a cheap USB GPS sensor for location?
> Is there a cheep USB GPS that provides PPS?  Any recommendations?
>
> I have seen simpler GPS controlled 10 MHz sources like the Miller design
> that divides down a 10 MHz ref and compares it to a 10 KHz output from a
> Jupiter T GPS to tweak the ref freq that may or may not be better suited to
> this application as it may add phase noise to the LO but would be more real
> time in it's GPS correction to the reference frequency.
>
> Regards,
>
>
> Norman Eric Haskell
>
> KC4YOE
>
> Keller, TX USA
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Redondo Beach, California
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Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Bob Camp]

Hi

The missing element in your evaluation is phase noise. If you directly multiply 
*any* 10 MHz source up to 
10 GHz, you have created a noise monster. The only rational way to do it is 
with a cleanup oscillator (or two)
somewhere between 10 MHz and 10 GHz. There are a variety of reasons why you get 
the noise increase and
multiple noise floors involved. 

If you pick something like 100 MHz as your (first?) cleanup, a bandwidth in the 
10 Hz region is not at all impractical 
with a narrowband OCXO as the 100 MHz source. For many decades microwave 
sources have been built this way.
There are *lots* of designs out there to look at. The power and complexity 
impact is minimal. 

Once you do that,  the only thing that matters on your 10 MHz is it’s long term 
stability. If you have the power budget,
a Rb is the obvious choice. If not, a DOCXO would be the right way to go. In 
either case, calibrate them before you 
take off on your “adventure”.

Bob

> On Dec 21, 2016, at 2:06 PM, Eric Haskell  wrote:
> 
> Hello Time Nuts,  I have been on the group and have promoted it to other 
> folks for a while but this may be my first post here.
> 
> I am microwave amateur radio operator and I have question to pose relating to 
> the use of GPSDO's with amateur radio for microwave communication.
> 
> First, the more generic question.  A friend was discussing using a eBay 
> purchased Trimble 57963-D for providing a 10 MHz refrence for his portable 
> microwave station  (primarly at 10GHz).  He wants a clean high stability 10 
> MHz refrence mainly to lock the station LO. First I think a GPSDO is overkill 
> for this application and I am thinking that a good surplus ovenized crystal 
> oscillator should get him to within a few Hz after warm up and a Rb could do 
> better but may have short term stability that may degrade phase noise of the 
> LO.  I am concerned that a GPSDO is not designed for portable operations.  
> Moving it should probably force a new site  survey which may take a day or 
> more  to complete before it goes into disciplining mode so you would loose 
> any potential benefit of a GPSDO by moving around frequently.  If he wants to 
> do this I think he should leave it connected at his home location for an 
> extended time (several days at least), then when he want to go portable 
> (roving), he shou
 ld
>  disconnect the GPS antenna entirely to force the unit into holdover mode 
> maintain continuous power with battery backup which should maintain the 
> internal OCXO very close to the target frequence and allow the holdover 
> algorithm to compensate for OCXO for aging and best it can.  I would guess 
> that if he chooses to used the GPSDO with the antenna connected it would 
> probably never exit the site survey mode and you would have the output 
> default to the last known good DAC value when it was been disciplined so it 
> would be operating as a OCXO only (although potentially starting from a very 
> accurate starting point, if it had been in use at a fixed location for a good 
> while) before going portable.  Is this a correct view of the situation?  Any 
> recommendations?
> 
> I also know of a fellow who has developed some excellent open source Linux 
> software to drive an Ettus Research USRP microwave SDR transceiver for 
> amateur radio microwave applications.  His code also has features to 
> calculate antenna baring and with other available code compensates for 
> satellite Doppler shift and/or synchronize digital communication modes using 
> the GPS coordinates and timing data.  He has a built in interface for a 
> Trimble Thunderbolt for this purpose.  I think it also might be a better 
> solution to use a OCXO for 10 MHz and a cheap USB GPS sensor for location?  
> Is there a cheep USB GPS that provides PPS?  Any recommendations?
> 
> I have seen simpler GPS controlled 10 MHz sources like the Miller design that 
> divides down a 10 MHz ref and compares it to a 10 KHz output from a Jupiter T 
> GPS to tweak the ref freq that may or may not be better suited to this 
> application as it may add phase noise to the LO but would be more real time 
> in it's GPS correction to the reference frequency.
> 
> Regards,
> 
> 
> Norman Eric Haskell
> 
> KC4YOE
> 
> Keller, TX USA
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[time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Eric Haskell]

Hello Time Nuts,  I have been on the group and have promoted it to other folks 
for a while but this may be my first post here.

I am microwave amateur radio operator and I have question to pose relating to 
the use of GPSDO's with amateur radio for microwave communication.

First, the more generic question.  A friend was discussing using a eBay 
purchased Trimble 57963-D for providing a 10 MHz refrence for his portable 
microwave station  (primarly at 10GHz).  He wants a clean high stability 10 MHz 
refrence mainly to lock the station LO. First I think a GPSDO is overkill for 
this application and I am thinking that a good surplus ovenized crystal 
oscillator should get him to within a few Hz after warm up and a Rb could do 
better but may have short term stability that may degrade phase noise of the 
LO.  I am concerned that a GPSDO is not designed for portable operations.  
Moving it should probably force a new site  survey which may take a day or more 
 to complete before it goes into disciplining mode so you would loose any 
potential benefit of a GPSDO by moving around frequently.  If he wants to do 
this I think he should leave it connected at his home location for an extended 
time (several days at least), then when he want to go portable (roving), he 
should
  disconnect the GPS antenna entirely to force the unit into holdover mode 
maintain continuous power with battery backup which should maintain the 
internal OCXO very close to the target frequence and allow the holdover 
algorithm to compensate for OCXO for aging and best it can.  I would guess that 
if he chooses to used the GPSDO with the antenna connected it would probably 
never exit the site survey mode and you would have the output default to the 
last known good DAC value when it was been disciplined so it would be operating 
as a OCXO only (although potentially starting from a very accurate starting 
point, if it had been in use at a fixed location for a good while) before going 
portable.  Is this a correct view of the situation?  Any recommendations?

I also know of a fellow who has developed some excellent open source Linux 
software to drive an Ettus Research USRP microwave SDR transceiver for amateur 
radio microwave applications.  His code also has features to calculate antenna 
baring and with other available code compensates for satellite Doppler shift 
and/or synchronize digital communication modes using the GPS coordinates and 
timing data.  He has a built in interface for a Trimble Thunderbolt for this 
purpose.  I think it also might be a better solution to use a OCXO for 10 MHz 
and a cheap USB GPS sensor for location?  Is there a cheep USB GPS that 
provides PPS?  Any recommendations?

I have seen simpler GPS controlled 10 MHz sources like the Miller design that 
divides down a 10 MHz ref and compares it to a 10 KHz output from a Jupiter T 
GPS to tweak the ref freq that may or may not be better suited to this 
application as it may add phase noise to the LO but would be more real time in 
it's GPS correction to the reference frequency.

Regards,


Norman Eric Haskell

KC4YOE

Keller, TX USA
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