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 
 To: Time Nuts  
 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" 
To: "Discussion of precise time and frequency measurement" 


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 
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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--

Chris Albertson
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] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[Tom Knox]

If it is any help, the 836XXA/B series are all capable of 1Hz resolution but 
are locked at 1KHz unless you enter the license key for option 008. So it could 
be software/firmware related.

Happy Merry;

Thomas Knox




From: time-nuts  on behalf of Dr. David Kirkby 
(Kirkby Microwave Ltd) 
Sent: Wednesday, December 21, 2016 4:42 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping 
up/down 100 Hz when not wanted.

I run a test over the weekend with a fellow radio ham. I transmitted 100 mW
or so at 10368.115 MHz from an HP 83623A 10 MHz to 20 GHz sweep generator

http://www.keysight.com/en/pd-101862%3Aepsg%3Apro-pn-83623A/synthesized-sweeper-10-mhz-to-20-ghz-high-power?cc=GB=eng
83623A Synthesized Sweeper, 10 MHz to 20 GHz, High Power [Obsolete] | Keysight 
(formerly Agilent’s Electronic 
Measurement)
www.keysight.com
The 83623A is no longer available, the replacement product is E8257D PSG analog 
signal generator.



into a small horn antenna inside my lab.

He was able to receive me about 7 km away, although the signal was quite
week - it was 20 dB above the noise in a 2.9 Hz bandwidth.

What is odd, is that his transceiver + transverter combination indicates
the signal generator is shifting frequency up/down 100 Hz. This is not slow
drift, but a step change - see waterfall picture, where time is on the
vertical axis, and frequency is on the horizontal. Unfortunately I don't
know what the scale is on the vertical axis - I am trying to find out. The
frequency on the x-axis is not the true frequency, but that shown on an 2 m
amateur transceiver, so the true frequency is more than 10 GHz higher.

The step size on this HP sweeper is 1 kHz, so the 100 Hz up/down shift is
not due to a rotary encoder that might be just on the limit of two
frequencies.  Both the internal oscillator and a GPS locked frequency
standard were used during this test. Going from internal to external
reference caused a 450 Hz step in frequency, but did not change this
up/down 100 Hz behavior. So the problem is certainly not the crystal in a
10 MHz reference oscillator, as two have been tried, one of which was
locked to GPS.

Does anyone have an idea what may cause this behavior?

Does anyone have any ideas on the best way to investigate this, given the
signal is at more than 10 GHz?

What I do *not* have is any other signal generator capable of operation at
10 GHz. The only other sig gen I have is a 30 MHz Stanford Research DS345
function generator.

I don't have a TI counter at the minute, but had an offer of $300 accepted
on eBay for a 5370B a couple of days back, so should have a TI counter
soon. (Yes, I have had an 5370B and SR620 in the past, but for various
reasons no longer have them). The 5370B at $300 was a lot cheaper than an
SR620.

Other equipment I have include

* 22 GHz spectrum analyzer
* 30 MHz signal generator
* 20 GHz VNA

but no other signal generator capable of anywhere near 10 GHz.

I do have a couple of double balanced mixers which have RF and IF inputs
that will take 10 GHz, and an IF output that will go from DC to 4 GHz.
Introducing a REALLY long delay might allow the steps to be seen, as the
frequency at the LO and RF inputs of the mixers will be different. But
that's not really practical, as I'd need an awfully long bit of coax.

The 20 GHz vector network analyzer, which could be pressed into service as
a poor (rich) mans microwave signal source, but I suspect the output of
that is quite dirty, as the output is generated from a step recovery diode.
I have not yet tested it on a spectrum analyzer, but the SA has quite a few
spurious signals, so I'm never exactly confident of the SA. But one thing
to possibly is

* Set sweep generator to 10.368 GHz
* Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
* Mix the VNA + sweeper down to 10 MHz using a double balanced mixer
* Compare the 10 MHz at the output of a mixer to that of a 10 MHz crystal.
Steps of 100 Hz should then be seen I guess.

Any better suggestions?

Someone had kindly given me a key to change the step size of the signal
generator from 1 kHz to 1 Hz. I've not applied that yet, as it is quite a
complex procedure. But the fact the step size of this is 1 kHz, but it is
shifting up/down 100 Hz, does not make sense. Especially given the unit is
capable of 1 Hz resolution, but HP decided to charge extra for 1 Hz steps.
Luckily this is just a software option.

I did wonder if the signal generator was incapable of output the exact
frequency needed, so it was stepped up/down periodically so it gave the
right number of cycles over a long duration. But again, the fact it can
step 1 Hz with just a software upgrade suggest that's not the case.

The 

[time-nuts] Ublox M8N - have I a XO or TCXO ?

[Mark Sims]

Lady Heather does issue the MON-VER command.  If you write a log file (W L W) 
the info is written as header comments in the log.  The 5.0 release only writes 
the first entry from the ROM info section.  The next spin will write all the 
available ROM info. My M8N returns 6 lines of ROM info (plus 8 blank lines)



> From my reading so far, the current best way to find out if you have a
genuine M8N is to use u-centre , and ask it to poll the UBX-MON-VER
command, which should return:
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Re: [time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[paul swed]

Dave Congratulations on 10 Ghz SSB.
Now to your question. I will fully believe you are seeing normal behavior
of the generators. Even if its dithering 100 Hz thats pretty amazing. Sweep
gens simply are not stable enough for narrow work like you are trying.
Now I am sure comments will prove me totally wrong.
But I don't think so. (Have been on 10G SSB over the years also. Only 60
watts plus. Nothing fancy. ;-)  )
Regards
Paul
WB8TSL

On Wed, Dec 21, 2016 at 7:31 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> On 21 December 2016 at 23:42, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk> wrote:
>
>
> > But one thing to possibly is
> >
> > * Set sweep generator to 10.368 GHz
> > * Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
> >
>
>
> I mean set the VNA to  10.378 GHz, so there's a 10 MHz difference between
> the VNA and sweep generator.
>
> Dave
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Re: [time-nuts] u-blox timing modules

[Scott Stobbe]

The LEA-M8F is a complete GPSDO in module, the TCXO is EFC steered, no
sawtooth needed.

On Wed, Dec 21, 2016 at 8:30 PM, Bob Camp  wrote:

> Hi
>
> Ummm…. because you need a 30.72 MHz reference in a 4G base station rather
> than the
> TCXO that normally is in the uBlox modules. You can then “carry” the
> sawtooth into the
> SDR part of the basestation without a lot of muss and fuss.
>
> Bob
>
> > On Dec 21, 2016, at 5:48 PM, Bob Stewart  wrote:
> >
> > Hi John,
> > Could you tell me why one would use choose an LEA-M8F over an LEA-M8T?
> > Bob - AE6RV
> >  -
> > AE6RV.com
> >
> > GFS GPSDO list:
> > groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> >
> >  From: John Haine 
> > To: time-nuts@febo.com
> > Sent: Wednesday, December 21, 2016 11:34 AM
> > Subject: [time-nuts] u-blox timing modules
> >
> > It's worth noting, in case people don't know, that u-blox have a
> > specific chip & module (the latter being the LEA-M8F) for precision
> > timing, developed for the LTE (4G) base station market. This disciplines
> > a low phase noise 30.72 MHz reference to received satellite signals,
> > GPS/GLONASS/BeiDou.  (30.72 MHz is the standard LTE sampling rate.)
> >
> > John.
> > ___
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> mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> >
> >
> > ___
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> mailman/listinfo/time-nuts
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>
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Re: [time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[Brooke Clarke]

Hi David:

Do you have a comb generator?

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 

I run a test over the weekend with a fellow radio ham. I transmitted 100 mW
or so at 10368.115 MHz from an HP 83623A 10 MHz to 20 GHz sweep generator

http://www.keysight.com/en/pd-101862%3Aepsg%3Apro-pn-83623A/synthesized-sweeper-10-mhz-to-20-ghz-high-power?cc=GB=eng

into a small horn antenna inside my lab.

He was able to receive me about 7 km away, although the signal was quite
week - it was 20 dB above the noise in a 2.9 Hz bandwidth.

What is odd, is that his transceiver + transverter combination indicates
the signal generator is shifting frequency up/down 100 Hz. This is not slow
drift, but a step change - see waterfall picture, where time is on the
vertical axis, and frequency is on the horizontal. Unfortunately I don't
know what the scale is on the vertical axis - I am trying to find out. The
frequency on the x-axis is not the true frequency, but that shown on an 2 m
amateur transceiver, so the true frequency is more than 10 GHz higher.

The step size on this HP sweeper is 1 kHz, so the 100 Hz up/down shift is
not due to a rotary encoder that might be just on the limit of two
frequencies.  Both the internal oscillator and a GPS locked frequency
standard were used during this test. Going from internal to external
reference caused a 450 Hz step in frequency, but did not change this
up/down 100 Hz behavior. So the problem is certainly not the crystal in a
10 MHz reference oscillator, as two have been tried, one of which was
locked to GPS.

Does anyone have an idea what may cause this behavior?

Does anyone have any ideas on the best way to investigate this, given the
signal is at more than 10 GHz?

What I do *not* have is any other signal generator capable of operation at
10 GHz. The only other sig gen I have is a 30 MHz Stanford Research DS345
function generator.

I don't have a TI counter at the minute, but had an offer of $300 accepted
on eBay for a 5370B a couple of days back, so should have a TI counter
soon. (Yes, I have had an 5370B and SR620 in the past, but for various
reasons no longer have them). The 5370B at $300 was a lot cheaper than an
SR620.

Other equipment I have include

* 22 GHz spectrum analyzer
* 30 MHz signal generator
* 20 GHz VNA

but no other signal generator capable of anywhere near 10 GHz.

I do have a couple of double balanced mixers which have RF and IF inputs
that will take 10 GHz, and an IF output that will go from DC to 4 GHz.
Introducing a REALLY long delay might allow the steps to be seen, as the
frequency at the LO and RF inputs of the mixers will be different. But
that's not really practical, as I'd need an awfully long bit of coax.

The 20 GHz vector network analyzer, which could be pressed into service as
a poor (rich) mans microwave signal source, but I suspect the output of
that is quite dirty, as the output is generated from a step recovery diode.
I have not yet tested it on a spectrum analyzer, but the SA has quite a few
spurious signals, so I'm never exactly confident of the SA. But one thing
to possibly is

* Set sweep generator to 10.368 GHz
* Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
* Mix the VNA + sweeper down to 10 MHz using a double balanced mixer
* Compare the 10 MHz at the output of a mixer to that of a 10 MHz crystal.
Steps of 100 Hz should then be seen I guess.

Any better suggestions?

Someone had kindly given me a key to change the step size of the signal
generator from 1 kHz to 1 Hz. I've not applied that yet, as it is quite a
complex procedure. But the fact the step size of this is 1 kHz, but it is
shifting up/down 100 Hz, does not make sense. Especially given the unit is
capable of 1 Hz resolution, but HP decided to charge extra for 1 Hz steps.
Luckily this is just a software option.

I did wonder if the signal generator was incapable of output the exact
frequency needed, so it was stepped up/down periodically so it gave the
right number of cycles over a long duration. But again, the fact it can
step 1 Hz with just a software upgrade suggest that's not the case.

The radio ham that noticed this step change in frequency is well used to
listening on 10 GHz, and hearing beacons. So I think its reasonable to
assume that the problem is not his end, but my end.

Any thoughts, which do NOT include purchasing a second expensive 20 GHz
signal generator. They are around $10,000 each, so a bit out of my price
range.

Dave


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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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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[Scott McGrath]

Can you use the VNA as a receiver? And determine whether the 100Hz shift is 
also seen on the VNA

> On Dec 21, 2016, at 7:31 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
>  wrote:
> 
> On 21 December 2016 at 23:42, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk> wrote:
> 
> 
>> But one thing to possibly is
>> 
>> * Set sweep generator to 10.368 GHz
>> * Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
> 
> 
> I mean set the VNA to  10.378 GHz, so there's a 10 MHz difference between
> the VNA and sweep generator.
> 
> Dave
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Re: [time-nuts] u-blox timing modules

[Bob Camp]

Hi

Ummm…. because you need a 30.72 MHz reference in a 4G base station rather than 
the 
TCXO that normally is in the uBlox modules. You can then “carry” the sawtooth 
into the 
SDR part of the basestation without a lot of muss and fuss. 

Bob

> On Dec 21, 2016, at 5:48 PM, Bob Stewart  wrote:
> 
> Hi John,
> Could you tell me why one would use choose an LEA-M8F over an LEA-M8T?
> Bob - AE6RV
>  -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> 
>  From: John Haine 
> To: time-nuts@febo.com 
> Sent: Wednesday, December 21, 2016 11:34 AM
> Subject: [time-nuts] u-blox timing modules
> 
> It's worth noting, in case people don't know, that u-blox have a 
> specific chip & module (the latter being the LEA-M8F) for precision 
> timing, developed for the LTE (4G) base station market. This disciplines 
> a low phase noise 30.72 MHz reference to received satellite signals, 
> GPS/GLONASS/BeiDou.  (30.72 MHz is the standard LTE sampling rate.)
> 
> John.
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> 
> 
> 
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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Kiwi Geoff]

Mike Cook wrote:
> It wouldn't surprise me, but  you have a reference for this?

I first read about this issue in the official Ublox forum Mike - try this link,

http://tinyurl.com/Fake-M8Ns

 - at time of writing it leads to some of the messages that discuss
the issue with photos and examples of M8N's that appear - not to be !

I must say, the two devices I have, appear to be genuine, and do
everything they should, and are a wonderful piece of kit.

My initial (now erroneous) thought was that maybe I could do a quick
overnight run with Lady Heather 5, to show up the M8N oscillator type.
Thanks to the excellent feedback on this thread, I now see why this is
not so, my overnight graph (seen in OP) is looking at a layer of
operation that somewhat hides the actual oscillator behaviour. I still
think it is an interesting graph, and shows the M8N can do a good job
of being a GNSS timing part.

Although as Mark S has said, it requires independent testing against a
reference to be done, rather than my graph - which essentially is the
M8N "self reporting" its quality.

>From my reading so far, the current best way to find out if you have a
genuine M8N is to use u-centre , and ask it to poll the UBX-MON-VER
command, which should return:

-
original firmware (2.01): SWVER 2.01 (75350) HWVER 0008 EXTENSION
2.01 (75331) PROTVER 15.00 FIS 0xEF4015 (79189) MOD NEO-M8N-0
GPS;SBAS;GLO;BDS;QZSS

after firmware update to (3.01): SWVER EXT CORE 3.01 (107900) HWVER
0008 EXTENSION ROM base 2.01 (75331) FWVER=SPG 3.01 PROTVER=18.00
FIS=0xEF4015 (100111) GPS;GLO;GAL;BDS;SBAS;IMES;QZSS
-

Take special note of the "FIS=" (Flash Information Structure) size.

Firmware Update to 3.01 can give you the (newly turned on) Galileo
system, however some people (like me) may choose to stay with Firmware
2.01 because it allows playing the RTK game thanks to the work of:

http://rtkexplorer.com/

Again, thank you for the replies to this thread, I have learned a lot,
and especially Bob Camp, who gave a nice explanation of the oscillator
in such a GNSS module.

Regards, Geoff (Christchurch, New Zealand).
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Re: [time-nuts] SR620: odd measurements when in remote control

[Hal Murray]

> on start up i have an odd behavior.

> 0, 1.99881895E+07
> 0, 1.99881912E+07
> 0, 1.99881757E+07
> 7, 1.99881856E+07
> 17, 1.99881878E+07
> 27, 1.99881900E+07

> What do you think?

Looks like you are expecting readings every 10 seconds but it's sending a few 
samples during startup and they are sitting in the system input buffer until 
you get around to reading them.

I would probably "fix" that by reading and discarding with a short timeout 
before dropping into the main loop.  That sort of code is often delicate 
since there might be one last chunk in the pipeline when your last read times 
out.  Plan B is to discard N samples where N is adjusted to include 1 or 2 of 
you main samples just to be sure.




-- 
These are my opinions.  I hate spam.



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[time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I run a test over the weekend with a fellow radio ham. I transmitted 100 mW
or so at 10368.115 MHz from an HP 83623A 10 MHz to 20 GHz sweep generator

http://www.keysight.com/en/pd-101862%3Aepsg%3Apro-pn-83623A/synthesized-sweeper-10-mhz-to-20-ghz-high-power?cc=GB=eng

into a small horn antenna inside my lab.

He was able to receive me about 7 km away, although the signal was quite
week - it was 20 dB above the noise in a 2.9 Hz bandwidth.

What is odd, is that his transceiver + transverter combination indicates
the signal generator is shifting frequency up/down 100 Hz. This is not slow
drift, but a step change - see waterfall picture, where time is on the
vertical axis, and frequency is on the horizontal. Unfortunately I don't
know what the scale is on the vertical axis - I am trying to find out. The
frequency on the x-axis is not the true frequency, but that shown on an 2 m
amateur transceiver, so the true frequency is more than 10 GHz higher.

The step size on this HP sweeper is 1 kHz, so the 100 Hz up/down shift is
not due to a rotary encoder that might be just on the limit of two
frequencies.  Both the internal oscillator and a GPS locked frequency
standard were used during this test. Going from internal to external
reference caused a 450 Hz step in frequency, but did not change this
up/down 100 Hz behavior. So the problem is certainly not the crystal in a
10 MHz reference oscillator, as two have been tried, one of which was
locked to GPS.

Does anyone have an idea what may cause this behavior?

Does anyone have any ideas on the best way to investigate this, given the
signal is at more than 10 GHz?

What I do *not* have is any other signal generator capable of operation at
10 GHz. The only other sig gen I have is a 30 MHz Stanford Research DS345
function generator.

I don't have a TI counter at the minute, but had an offer of $300 accepted
on eBay for a 5370B a couple of days back, so should have a TI counter
soon. (Yes, I have had an 5370B and SR620 in the past, but for various
reasons no longer have them). The 5370B at $300 was a lot cheaper than an
SR620.

Other equipment I have include

* 22 GHz spectrum analyzer
* 30 MHz signal generator
* 20 GHz VNA

but no other signal generator capable of anywhere near 10 GHz.

I do have a couple of double balanced mixers which have RF and IF inputs
that will take 10 GHz, and an IF output that will go from DC to 4 GHz.
Introducing a REALLY long delay might allow the steps to be seen, as the
frequency at the LO and RF inputs of the mixers will be different. But
that's not really practical, as I'd need an awfully long bit of coax.

The 20 GHz vector network analyzer, which could be pressed into service as
a poor (rich) mans microwave signal source, but I suspect the output of
that is quite dirty, as the output is generated from a step recovery diode.
I have not yet tested it on a spectrum analyzer, but the SA has quite a few
spurious signals, so I'm never exactly confident of the SA. But one thing
to possibly is

* Set sweep generator to 10.368 GHz
* Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
* Mix the VNA + sweeper down to 10 MHz using a double balanced mixer
* Compare the 10 MHz at the output of a mixer to that of a 10 MHz crystal.
Steps of 100 Hz should then be seen I guess.

Any better suggestions?

Someone had kindly given me a key to change the step size of the signal
generator from 1 kHz to 1 Hz. I've not applied that yet, as it is quite a
complex procedure. But the fact the step size of this is 1 kHz, but it is
shifting up/down 100 Hz, does not make sense. Especially given the unit is
capable of 1 Hz resolution, but HP decided to charge extra for 1 Hz steps.
Luckily this is just a software option.

I did wonder if the signal generator was incapable of output the exact
frequency needed, so it was stepped up/down periodically so it gave the
right number of cycles over a long duration. But again, the fact it can
step 1 Hz with just a software upgrade suggest that's not the case.

The radio ham that noticed this step change in frequency is well used to
listening on 10 GHz, and hearing beacons. So I think its reasonable to
assume that the problem is not his end, but my end.

Any thoughts, which do NOT include purchasing a second expensive 20 GHz
signal generator. They are around $10,000 each, so a bit out of my price
range.

Dave
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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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Re: [time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 21 December 2016 at 23:42, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:


> But one thing to possibly is
>
> * Set sweep generator to 10.368 GHz
> * Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
>


I mean set the VNA to  10.378 GHz, so there's a 10 MHz difference between
the VNA and sweep generator.

Dave
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Re: [time-nuts] u-blox timing modules

[Bob Stewart]

Hi John,
Could you tell me why one would use choose an LEA-M8F over an LEA-M8T?
Bob - AE6RV
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: John Haine 
 To: time-nuts@febo.com 
 Sent: Wednesday, December 21, 2016 11:34 AM
 Subject: [time-nuts] u-blox timing modules
   
It's worth noting, in case people don't know, that u-blox have a 
specific chip & module (the latter being the LEA-M8F) for precision 
timing, developed for the LTE (4G) base station market. This disciplines 
a low phase noise 30.72 MHz reference to received satellite signals, 
GPS/GLONASS/BeiDou.  (30.72 MHz is the standard LTE sampling rate.)

John.
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[time-nuts] Back Time nutting and a GPStar Plus

[George Atkinson]

Hi,

I've been absent from the list for a few years. A combination of relocation for
work, and other stuff going on. I'd not stopped altogether though. I have got an
antenna on the new QTH, my Thunderbolt boxed up and running and some other test
equipment sorted.  Any way I randomly typed Odetics into eBay (UK) last week and
a 365 GPStar Plus time source / GPSDO popped up as a BIN. It appeared to be
brand new in the original box and complete apart from the antenna. I made an
offer and won it for under $100. It turned up promptly and sure enough is NOS,
the power connector has never been made off. It's all working, but being a 1995
model it has the Magellen OEM5000 GPS engine so has the wrong date due to the
week rollover issue. Back in 2012 Arthur Dent tried a Zyfer 565 GPStar Plus
EPROM in a later Oncore engined 365 and it all worked. Rob Kimberley confirmed
that this was the only difference between the 1995 Odetics 365 and the current
Zyfer 565. Back then I got a BIN file of the EPROM (thanks Arthur) even though I
had no 365. I burnt a 27C010 last night and the 365 runs with it fitted, but as
expected does not recognise the GPS. So tonight I dug out  Oncore UT+
(R5122U-1153) to make a retrofit. Next step is to identify the connetions to the
GPS module. I have some OEM5000 info and some probing should sort that out. I do
wonder if anyone else has tried this and has the connection information already?
Oh nd as a bonus I will have a spare OEM5000 to retrofit my fully loaded,
including Rb oscillator, 325 SatSync (currently needs a down converter antenna
which I don't have) so I can get that working if I ever get it out of the back
of the garage.

Robert G8RPI.
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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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[time-nuts] u-blox timing modules

[John Haine]

It's worth noting, in case people don't know, that u-blox have a 
specific chip & module (the latter being the LEA-M8F) for precision 
timing, developed for the LTE (4G) base station market. This disciplines 
a low phase noise 30.72 MHz reference to received satellite signals, 
GPS/GLONASS/BeiDou.  (30.72 MHz is the standard LTE sampling rate.)


John.
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[time-nuts] SR620: odd measurements when in remote control

[lincoln]

Hello, 
I have an SR620 that i am trying to get some more life out of. I have 
dedicated a raspberry pi 2 to recode data and make the files available through 
the network. I wrote a small c deamond that will setup the counter to make 
frequency measurements and  save the result to a file on the flash card. 

Overall it is basically working but on start up i have an odd behavior. 

My file format is a "two column " file, column 1 is elapsed system time in 
seconds,  and column 2 is the measurement returned by the counter.  When the 
program starts I get 2 to 5 measurements that are wrong. A number of 
measurement are returned in the first second, 

How I setup the counter: 
// get id of counter, if it is not an sr620, exit with error;
fprintf(stream,"*RST\n");  // system reset
sleep(10);
fprintf(stream,"CLCK 1\n"); // external timebase
fprintf(stream,"AUTM 0\n"); // automatic masurment off
fprintf(stream,"MODE 3\n"); // mesure freqency
fprintf(stream,"GATE1 E1\n"); // set for 10 second gate
fprintf(stream,"SIZE 1\n");// 1 sample per mesurment
fprintf(stream,"TERM 1, 0\n"); // 50 ohm termination for 
channel "A"
fprintf(stream,"LEVL 1, 0\n"); // trigger level 0.00
fprintf(stream,"TCPL 1, 1\n"); // AC coupling, channel A
sleep(4);
// pause for a bit

loop until quite {
fprintf(stream,"STRT;*WAI;XAVG?\n"); // start 
measurement, wait till complete, 
while ((bytesread = getline(from serial port stream) != 
-1) { // will block until full line 
if (bytesread >10) break;
}
// write data to file,
}

// close serial port
// close data file


example output:

#type=Freq
#start_date=1482003092 
#f_nom=2e+7
0, 1.99881895E+07
0, 1.99881912E+07
0, 1.99881757E+07
7, 1.99881856E+07
17, 1.99881878E+07
27, 1.99881900E+07
37, 1.99881877E+07
47, 1.99881908E+07
57, 1.99881921E+07

What do you think?

Link

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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Bob Camp]

Hi

Given the short term stability limits on the frequency source (TCXO or XO) it’s 
a pretty
good bet that the crystal in both oscillators is very similar. There’s not a 
lot of difference
between a “normal” crystal and a “TCXO” crystal other than the angle of cut 
tolerance. 
Since the XO has frequency rate of change specs on it for the GPS to work, it’s 
got
some angle limits that get it pretty close to TCXO land even in that regard.

Bob


> On Dec 21, 2016, at 8:43 AM, Peter Reilley  wrote:
> 
> You seem to be assuming that the crystal in the TCXO is the same as the 
> crystal in the XO.
> Wouldn't it be likely that the crystal would be higher quality in the more 
> expensive
> product; the TCXO?   How would a cheap crystal vs an expensive crystal appear 
> different
> in the GPS data presented (ignoring the TC part)?
> 
> Pete.
> 
> 
> On 12/21/2016 7:37 AM, Bob Camp wrote:
>> Hi
>> 
>>> On Dec 21, 2016, at 4:20 AM, Mike Cook  wrote:
>>> 
>>> 
 Le 21 déc. 2016 à 00:08, Kiwi Geoff  a écrit :
 
 Hello All - and Seasons Greetings,
 
 One of the advantages of the recent hobby drone phenomena - it has
 brought to the market a lot of low cost GNSS modules that are
 lightweight for drone flight control systems. Those of us with other
 hobbies, like "Time Nuts" and RTK - these low cost modules can be a
 little goldmine for cost effective toys.
 
 However the dark side is that some vendors are re-badging lower cost
 modules, printing their own labels and marking as "Ublox M8N" for
 example.
>>> It wouldn't surprise me, but  you have a reference for this?
>>> 
 Can anyone comment on the following data, and whether they think the
 oscillator in "my" M8N is a XO or a TCXO ?
 
>>> I don’t thing that you can get find out from that data. Ublox indicate in 
>>> the product info sheets that the TCXO option is used to get to a first fix 
>>> quicker in weak signal conditions. It is not specified and I think that it 
>>> is logical, that there is an improved timing solution. I would expect that 
>>> both XO and TCXO versions are the same frequency and the better long term 
>>> stability of a TCXO not be an influence on the single shot quantization 
>>> error of the 1PPS.
>> 
>> The TCXO and XO both have similar short term stability at short tau. The only
>> advantage to the TCXO is faster time to first fix. If anything the XO will 
>> “spread”
>> the quantization error (sawtooth error) better than the TCXO. The TCXO has
>> more inflections in it’s frequency vs temperature curve. Thus there are more
>> opportunities for hanging bridges.
>> 
>> In both the TCXO and XO case, the PPS out of the module is based on the
>> clock edge closest to the PPS estimate. If the clock involved has a period of
>> 20 ns, the error will distribute over ~ +/- 10 ns. The process is identical 
>> regardless
>> of the oscillator. The distribution will be the same with both oscillators. 
>> As long as the
>> phase noise and short tau ADEV are in spec, the PPS estimate will be the same
>> in both cases.
>> 
>> Bob
>> 
>>> 
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 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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>>> "The power of accurate observation is commonly called cynicism by those who 
>>> have not got it. »
>>> George Bernard Shaw
>>> 
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[time-nuts] Ublox M8N - have I a XO or TCXO ?

[Mark Sims]

I have used Reyax modules with RS-232 outputs for a long time.  The company 
seems to be quite good.  I trust them to be a reliable supplier and have never 
had any problems with any of their units despite being used in some rather 
harsh conditions.



>  Some time ago, I bought two different modules from Reyax on ebay. One
module had a ublox M8N. Recently, I did some reading on several drone
forums about fake ublox modules from China. It seems that modules from
quite a few vendors are not genuine. From the information presented
about identifying the fakes, I am fairly confident that the modules I
bought from Reyax are genuine.
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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Peter Reilley]

You seem to be assuming that the crystal in the TCXO is the same as the 
crystal in the XO.
Wouldn't it be likely that the crystal would be higher quality in the 
more expensive
product; the TCXO?   How would a cheap crystal vs an expensive crystal 
appear different

in the GPS data presented (ignoring the TC part)?

Pete.


On 12/21/2016 7:37 AM, Bob Camp wrote:

Hi


On Dec 21, 2016, at 4:20 AM, Mike Cook  wrote:



Le 21 déc. 2016 à 00:08, Kiwi Geoff  a écrit :

Hello All - and Seasons Greetings,

One of the advantages of the recent hobby drone phenomena - it has
brought to the market a lot of low cost GNSS modules that are
lightweight for drone flight control systems. Those of us with other
hobbies, like "Time Nuts" and RTK - these low cost modules can be a
little goldmine for cost effective toys.

However the dark side is that some vendors are re-badging lower cost
modules, printing their own labels and marking as "Ublox M8N" for
example.

It wouldn't surprise me, but  you have a reference for this?


Can anyone comment on the following data, and whether they think the
oscillator in "my" M8N is a XO or a TCXO ?


I don’t thing that you can get find out from that data. Ublox indicate in the 
product info sheets that the TCXO option is used to get to a first fix quicker 
in weak signal conditions. It is not specified and I think that it is logical, 
that there is an improved timing solution. I would expect that both XO and TCXO 
versions are the same frequency and the better long term stability of a TCXO 
not be an influence on the single shot quantization error of the 1PPS.


The TCXO and XO both have similar short term stability at short tau. The only
advantage to the TCXO is faster time to first fix. If anything the XO will 
“spread”
the quantization error (sawtooth error) better than the TCXO. The TCXO has
more inflections in it’s frequency vs temperature curve. Thus there are more
opportunities for hanging bridges.

In both the TCXO and XO case, the PPS out of the module is based on the
clock edge closest to the PPS estimate. If the clock involved has a period of
20 ns, the error will distribute over ~ +/- 10 ns. The process is identical 
regardless
of the oscillator. The distribution will be the same with both oscillators. As 
long as the
phase noise and short tau ADEV are in spec, the PPS estimate will be the same
in both cases.

Bob




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have not got it. »
George Bernard Shaw

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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Joseph Gray]

Some time ago, I bought two different modules from Reyax on ebay. One
module had a ublox M8N. Recently, I did some reading on several drone
forums about fake ublox modules from China. It seems that modules from
quite a few vendors are not genuine. From the information presented
about identifying the fakes, I am fairly confident that the modules I
bought from Reyax are genuine.

Joe Gray
W5JG
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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Bob Camp]

Hi

> On Dec 21, 2016, at 4:20 AM, Mike Cook  wrote:
> 
> 
>> Le 21 déc. 2016 à 00:08, Kiwi Geoff  a écrit :
>> 
>> Hello All - and Seasons Greetings,
>> 
>> One of the advantages of the recent hobby drone phenomena - it has
>> brought to the market a lot of low cost GNSS modules that are
>> lightweight for drone flight control systems. Those of us with other
>> hobbies, like "Time Nuts" and RTK - these low cost modules can be a
>> little goldmine for cost effective toys.
>> 
>> However the dark side is that some vendors are re-badging lower cost
>> modules, printing their own labels and marking as "Ublox M8N" for
>> example.
> 
> It wouldn't surprise me, but  you have a reference for this? 
> 
>> Can anyone comment on the following data, and whether they think the
>> oscillator in "my" M8N is a XO or a TCXO ?
>> 
> 
> I don’t thing that you can get find out from that data. Ublox indicate in the 
> product info sheets that the TCXO option is used to get to a first fix 
> quicker in weak signal conditions. It is not specified and I think that it is 
> logical, that there is an improved timing solution. I would expect that both 
> XO and TCXO versions are the same frequency and the better long term 
> stability of a TCXO not be an influence on the single shot quantization error 
> of the 1PPS. 


The TCXO and XO both have similar short term stability at short tau. The only 
advantage to the TCXO is faster time to first fix. If anything the XO will 
“spread” 
the quantization error (sawtooth error) better than the TCXO. The TCXO has
more inflections in it’s frequency vs temperature curve. Thus there are more
opportunities for hanging bridges. 

In both the TCXO and XO case, the PPS out of the module is based on the 
clock edge closest to the PPS estimate. If the clock involved has a period of 
20 ns, the error will distribute over ~ +/- 10 ns. The process is identical 
regardless
of the oscillator. The distribution will be the same with both oscillators. As 
long as the
phase noise and short tau ADEV are in spec, the PPS estimate will be the same
in both cases. 

Bob

> 
> 
>> _
>> 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.
> 
> "The power of accurate observation is commonly called cynicism by those who 
> have not got it. »
> George Bernard Shaw
> 
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Re: [time-nuts] Ublox M8N - have I a XO or TCXO ?

[Mike Cook]

> Le 21 déc. 2016 à 00:08, Kiwi Geoff  a écrit :
> 
> Hello All - and Seasons Greetings,
> 
> One of the advantages of the recent hobby drone phenomena - it has
> brought to the market a lot of low cost GNSS modules that are
> lightweight for drone flight control systems. Those of us with other
> hobbies, like "Time Nuts" and RTK - these low cost modules can be a
> little goldmine for cost effective toys.
> 
> However the dark side is that some vendors are re-badging lower cost
> modules, printing their own labels and marking as "Ublox M8N" for
> example.

It wouldn't surprise me, but  you have a reference for this? 

> Can anyone comment on the following data, and whether they think the
> oscillator in "my" M8N is a XO or a TCXO ?
> 

I don’t thing that you can get find out from that data. Ublox indicate in the 
product info sheets that the TCXO option is used to get to a first fix quicker 
in weak signal conditions. It is not specified and I think that it is logical, 
that there is an improved timing solution. I would expect that both XO and TCXO 
versions are the same frequency and the better long term stability of a TCXO 
not be an influence on the single shot quantization error of the 1PPS. 


> _
> 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.

"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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Re: [time-nuts] Lady Heather Version 5 is now available

[Peter Putnam]

Mark,

Thank you very much for the effort you put into the new Lady Heather 
Version 5 code.


Comments from other linux users encouraged me to try my luck with a 
Raspberry Pi 2 Model B. The code compiled without issue and runs perfectly.


The pre-configured "heather.cfg" file is a nice touch, considering the 
many new options. Old options add in easily.



Regarding the Raspberry Pi display...

I started with a large LCD monitor with a native resolution of 1280 x 
1024. Using an HDMI to DVI cable, LH5 put out a very nice display using 
perhaps 80% of the available screen area.


In order to put an older 1024 x 768 VGA monitor into service, an HDMI to 
VGA adapter is required. For those worrying about the ability of the 
HDMI output to provide enough current to power the adapter, I can 
confirm the IOGear GVC311 HD to VGA adapter draws only 150 mA, well 
within the 200 mA rating of the diode protecting the port from reverse 
bias. The processor alone draws 300 mA, so the total current at 5 volts 
is 450 mA, allowing me to add both to the 5-volt output of the 
Thunderbolt's UPS-protected power supply.


The initial result was OK except the graph area at the bottom was only 8 
lines high, instead of the 10 lines I expected. In addition, some unused 
space appeared below the graph. Efforts to "resize" or change 
screen-edge values in the Raspbian config.txt file proved futile. 
However, right-clicking on the Panel bar at the top of the screen and 
resizing the icons to 28 pixels and the bar itself to 30 pixels did the 
trick. Now the graph area is 10 lines high and the screen is fully utilized.


Thanks, again, Mark, for a job well done.

Regards,
Peter


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