[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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