[time-nuts] time-nuts Digest, Vol 27, Issue 28

John Ackermann N8UR jra at febo.com
Mon Oct 23 13:18:13 EDT 2006


Hi Dave --

I'll try to get it uploaded in the next day or two.  I'll report back 
the URL once I know what it will be.

73,
John
----

fre_eng at g4fre.com wrote:
> Interestingly I asked around 50% of this question in person to John 
> Ackermann at microwave update saturday afternoon. My special interest was 
> what commands to send to the 5370a through the HPIB to generate the txt file 
> need by Alavar 
> 
> John
> Did you get round to uploading the .ppt...especially interested in the  Gerd 
> curtailed part! 
> 
> Dave 
> 
> WW2R 
> 
>> Message: 3
>> Date: Sun, 22 Oct 2006 00:29:14 -0500
>> From: Didier Juges <didier at cox.net>
>> Subject: [time-nuts] How to measure Allan Deviation?
>> To: Discussion of precise time and frequency measurement
>> 	<time-nuts at febo.com>
>> Message-ID: <453B01AA.2010109 at cox.net>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed 
>>
>> OK, here is my problem. I do not think it is a unique problem, based on 
>> recent mail :-) 
>>
>> I have read about the Allan Deviation and I understand the principle, 
>> even though the nuances between the 3 basic Allan deviations escape me 
>> at the moment, but I am sure it will come once I re-read the Help file 
>> that comes with the the AlaVar software , and I have downloaded and 
>> installed AlaVar, a free software that can compute the various flavors 
>> of the Allan Deviation. 
>>
>> I have a working HP 5370A, which I believe is required (even though 
>> maybe other counters, such as the HP 5334 or HP 5316, both of which have 
>> a TI function that  might be used for that purpose) to gather the data 
>> that will be fed into AlaVar. 
>>
>> I have a working GPIB interface (actually several types) and a computer 
>> attached to it, and I can write a Visual Basic programs to talk to the 
>> counter and download data (I have already written Visual Basic/GPIB 
>> programs to control signal generators, power meter, spectrum analyzers 
>> and other instruments). 
>>
>> I have several HP 10811 oscillators (with EFC input), and a couple of 
>> Ovenair (also with EFC input for at least one of them), some are inside 
>> working HP instruments, and a couple are spares. 
>>
>> What I do not have is a procedure. What data do I need to feed the 
>> software and how do I actually collect the data? 
>>
>> I assume the 5370 should be set to measure TI between 2 oscillators. 
>> Should I use the built-in averaging function? What sample size and 
>> resolution should I use? Should I try to use the 5370 in raw mode (much 
>> faster, 6000 samples/sec) or in formatted mode (10-20 samples/sec)? Does 
>> it make a difference?
>> What if the oscillators are not phase locked and show frequency drift? 
>>
>> The 5370 has a 10811 oscillator for its time base, so it is good but no 
>> better than any of the oscillators I want to check. Do I use it as a 
>> reference, or do I compare two stand-alone oscillators? 
>>
>> How do I know which oscillator I am measuring when the two oscillators I 
>> am comparing are the same models? Should I compare 3 or more? 
>>
>> Regarding the GPS receiver, I thought most modern GPS receivers 
>> automatically switch from nav mode to survey mode when they stop moving. 
>> I would probably be mistaken to believe this is comparable to a true 
>> time-keeping GPS receiver, but how bad is it? Tom Clark wrote previously 
>> on Time-Nuts that his experience with the Jupiter was good, with +/- 13 
>> nS jitter, other than the fact the receiver will not return the timing 
>> error on the next pulse, which prevents from writing smart software that 
>> can compensate for it. 
>>
>> I have a Jupiter GPS receiver which I intend to use to discipline one of 
>> the 10811 oscillators. The Jupiter receiver has a 10kHz output, which 
>> would simplify the phase lock loop a little (even though it would not 
>> allow to speed up the loop). Is there any disadvantage in using it 
>> instead of the 1PPS output? It seems the 10 kHz would be easier to 
>> filter,  and maybe allow to speed up the loop following power up 
>> (assuming it is set to the normal, longer time constant once phase lock 
>> is achieved), but what do I know? 
>>
>> I also have a modified distribution amplifier to distribute the good 10 
>> MHz to my lab without affecting the master oscillator. 
>>
>> So I am anxious to use the AlaVar software and the toys I have listed 
>> above to do the following: 
>>
>> 1) select the best OCXO to be the basis of my GPS disciplined frequency 
>> standard
>> 2) find the best placement for the GPS antenna (the one that gives the 
>> most stable GPS signal)
>> 3) fine tune the phase lock parameters and estimate the quality of the 
>> end product 
>>
>> Any further information and guidance (with practical tips) would be 
>> greatly appreciated. 
>>
>> Didier KO4BB 
>>
>>
>  
> 
> 
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