[GPS_Standard] Re: GPS_Standard Digest, Vol 8, Issue 2

Sun Jun 10 14:55:05 EDT 2007

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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>>
>>
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>>End of GPS_Standard Digest, Vol 8, Issue 2
>>******************************************
>>
>>
>
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