[GPS_Standard] Re: GPS_Standard Digest, Vol 8, Issue 4

Wed Jun 13 17:21:49 EDT 2007

Hi Jacques
Thanks for your comments and the link to your new graph in the vcxo 
analysis file. Your plot at 80+ hours is looking similar to what I'm 
getting.

My system has now been running for about 2 weeks and I am taking some 
more readings to plot the longer term drift.
The frequency difference (relative to my10MHz rubidium source) is 
currently down to about 0.0015 Hz and over the last 12 hours or so the 
variation indicated by the DAC voltage has been very low. Now the OCXO 
seems to be settling down after the intial warm up it will be 
interesting to see how much xtal ageing and/or frequency jumps affect 
the DAC control voltage.

Regards
Chris, G3WCD
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 10 Jun 2007 14:55:05 -0400
> From: "jacques audet" <jaudet at hotmail.com>
> Subject: RE: [GPS_Standard] Re: GPS_Standard Digest, Vol 8, Issue 2
> To: c.r.dillon at dsl.pipex.com, gps_standard at mailman.qth.net
> Message-ID: <BAY102-F2146B6181A0974C200FF50C41B0 at phx.gbl>
> Content-Type: text/plain; charset=iso-8859-1; format=flowed
>
> Hello Chris,
>
> On my system with a HP10544A  VCXO, it took at least 80 hours for the DAC to 
> stabilize.
> See:  http://www.geocities.com/ve2_azx/
> Select:   Modifications and Analysis of VE2ZAZ Frequency Standard.
> I have added a graph in the  VCXO_Analysis.pdf  file.
>
> regards
> Jacques Audet
> VE2AZX
>
>
>
>
>   
>> From: Chris Dillon <c.r.dillon at dsl.pipex.com>
>> To: gps_standard at mailman.qth.net
>> Subject: [GPS_Standard] Re: GPS_Standard Digest, Vol 8, Issue 2
>> Date: Sat, 09 Jun 2007 14:54:56 +0100
>>
>> Hi Bert - many thanks for your very helpful comments.
>>
>> I disconnected the switch and checked out the pulse shape on the board 
>> itself but it seems not to be too badly affected by the wiring. The edges 
>> are clean, the counter clocks OK and, when terminated by 50 ohm loads, the 
>> outputs from the driver are all clean. I mounted all the boards on a copper 
>> ground plane and ran all wiring close to that so that may help. I guess 
>> that if distortion is a problem in this type of application one approach 
>> would be to switch remotely using a sub-miniature signal relay mounted 
>> close to the board.
>>
>> I've since run some tests against my rubidium source, which has a 
>> calibrated accuracy of 0.48E-10. Comparing outputs on a scope the rate of 
>> change of phase of the GPS relative to the rubidium is 1 cycle over about 
>> 400 seconds - indicating a frequency difference  of about 0.0025 Hz. This 
>> is with an average sample size of 512. On MonTrol the average frequency 
>> offset is coming out in the low E-10s.
>>
>> One thing I have noticed is that the trend of the DAC output is still to 
>> gradually creep up. It will be interesting to see if this slow creep tails 
>> off as the HP 10811 OCXO (and everything else) warms up over the next 30 
>> days or so. Any comments on long term stability from your measurements, 
>> Bert?
>>
>> Best wishes
>>
>> Chris, G3WCD
>>     
>>> ----------------------------------------------------------------------
>>>
>>> Message: 1
>>> Date: Mon, 4 Jun 2007 14:52:18 -0400
>>> From: "Bert, VE2ZAZ" <ve2zaz at sympatico.ca>
>>> Subject: Re: [GPS_Standard] GPS  standard up and running To: "Chris 
>>> Dillon" <c.r.dillon at dsl.pipex.com>,
>>> 	<GPS_Standard at mailman.qth.net>
>>> Message-ID: <1CDA7C3EBF5A407AA526D267C2F5F739 at zaub2>
>>> Content-Type: text/plain;	charset="iso-8859-1"
>>>
>>> Hi Chris,
>>>
>>> Thanks for your kind words regarding my project. I am happy to hear that 
>>> you
>>> are happy with the results. I can see that you have spent time adding
>>> features and improvements you felt would make it even more enjoyable.
>>>
>>> One small comment I have is regarding the 5/1 MHz switch you have added. 
>>> The
>>> only reason why I kept this feature with an on-board jumper as opposed to
>>> controlling it via the PIC micro is that the actual 10MHz signal passes
>>> through the jumper contacts. If you extend these with leads to a toggle
>>> switch, you will definitely distort the pulse shape going into the decade
>>> counter. By how much? You are the best person to confirm! As a bare 
>>> minimum,
>>> I would keep the leads as short as possible and use a good quality switch.
>>> Maybe some small coax would also improve.
>>>
>>> Enjoy!
>>>
>>> Bert, VE2ZAZ
>>>
>>>
>>> ----- Original Message -----
>>> From: "Chris Dillon" <c.r.dillon at dsl.pipex.com>
>>> To: <GPS_Standard at mailman.qth.net>
>>> Sent: Friday, June 01, 2007 2:09 PM
>>> Subject: [GPS_Standard] GPS standard up and running
>>>
>>>
>>> Hi Bert - I've just completed the GPS standard and wanted to thank you
>>> for a great project.
>>>
>>> It's taken about 6 months since I bought the board and PIC from you but
>>> at last it is working and in a case. My version uses a Rockwell Jupiter
>>> GPS receiver board with an HP 10811 OCXO. I incorporated Jacques'
>>> (VE2AZX) mods to the PCB and also added a 78L05 regulator to supply the
>>> PIC alone. This fits on the board (with the appropriate tracks cut) just
>>> in front of the main 7805 regulator. Following Jacques I brought out the
>>> 1 pps to the front panel, and also added a toggle switch to select  a 1
>>> or 5 MHz output from one of the front BNC sockets.
>>>
>>> So that I could read the NMEA strings from the Jupiter GPS - and display
>>> satellite data (using the TAC32 demo software) - I arranged to be able
>>> to switch between the Jupiter and PCB serial outputs before going to the
>>> MAX232 TTL-RS232 converter.
>>>
>>> The system has now been running for about 36 hours. I'm using an average
>>> sample size (S) of 64 and voting mode. Initially I set up the OCXO so
>>> that it was running within about +0.01Hz of 10MHz with a control voltage
>>> close to zero (0x01EAB - DAC value 7851). From that start the FLL locked
>>> in about 160 secs. As it warmed up it drifted low towards 10 MHz and now
>>> appears to be stabilising at 0x01FD1 (DAC value 8145).  The average
>>> frequency offset  shown by MonTrol is around the low E-10s with the
>>> accumulated total around 4E-10. Standard deviation is about 1.3E-8.
>>>
>>> I've not yet compared this with my rubidium standard but this
>>> performance so far seems pretty good to me for a relatively short warm
>>> up time and small sample size. I'll keep an eye on it and see how it
>>> goes over the next few hours - and perhaps increase the sampling time to
>>> an hour or so to see if it makes any difference.
>>>
>>> Thanks again Bert - especially for the PCB, pre-programmed PIC, Montrol
>>> software and manual - you've done a great job!
>>>
>>> Kind regards
>>>
>>> Chris, G3WCD
>>>
>>>
>>>
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>>> End of GPS_Standard Digest, Vol 8, Issue 2
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>>>
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> End of GPS_Standard Digest, Vol 8, Issue 4
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>   