[time-nuts] Newbie questions

[Bruce Griffiths]

One should of course be aware that the number notation used is no longer 
considered correct.

Also even after correcting for the non standard notation the last set of 
numbers is incorrect:

eg
40.000 000 003 GHz  is equivalent to an error of  +7.5 parts in 1E11 not 
7.5 parts in 1E-11.

Bruce

Tom Duckworth wrote:
> Jim,
>
> Attached is some info on how to measure/calibrate a time base or 
> oscillator which you might find useful per your e-mail.
>
> Tom
> Tom Duckworth
> tomduck at comcast.net
> ----- Original Message ----- From: "Jim Mandaville" <zygo at dakotacom.net>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Sent: Tuesday, January 05, 2010 11:17 AM
> Subject: [time-nuts] Newbie questions
>
>
>> I am new to the list (although lurking now a while) and also new to 
>> the more precise species of  frequency and time measurement.  I have 
>> recently powered up an LPro and a Thunderbolt, both of which appear 
>> to be working by the book.  Connecting the TBolt to my scope external 
>> sync and the LPro as an "unknown" I see the pattern moving one 
>> division (cm) to the left in 295 seconds with a 0.05 us-per-division 
>> setting on the scope (the fastest setting available).  This, if my 
>> newly-learned calculations are correct, indicates a difference of 1.7 
>> X10-10 (0.0017 Hz).  This appears to be confirmed by my HP 5335A 
>> counter, which shows the LPRO 1or 2 thousandths of a Hz low, using 
>> the TBolt as an external time source. An HP manual I have indicates 
>> that a low unknown pattern should be moving to the right, not the 
>> left, on the scope, so this sort of puzzles me.
>>
>> I have a few questions that I'm hoping some of you more experienced 
>> hands can help with:
>>
>> 1.  Can someone tell me the meaning and significance of the "Timing 
>> Outputs" numbers in the lower left corner of the TBolt monitor 
>> window? (Mine right now is showing plus 3.75 ns and plus 0.01 ppb). 
>> The TBolt manual does not describe these, although on one page it 
>> lists them as "estimates of UTC/GPS offsets."  Do these numbers show 
>> the difference between my receiver outputs and the time being kept by 
>> my present satellites?  Or is it the difference between my receiver 
>> outputs and master gps time (somewhere)?  Neither of these?  The use 
>> of two decimal places on nanoseconds implies great accuracy.  Is this 
>> obtained in practice?  My ppb on 10 MHz usually lies between plus 0.1 
>> and minus 0.1, often hanging around 0.01 or 0.02.  I have not so far 
>> put in any compensation for cable delay.
>>
>> If the TBolt "knows" what these differences are, why doesn't it just 
>> factor them into its outputs?  Or does it?
>>
>> 2.  What is a reasonable expectation of TBolt accuracy (at any given 
>> time that I use it for measurement) for the 10 MHz relative to NIS? 
>> How accurate would it be, say, 90 percent of the time? (Looking for 
>> just an experienced guesstimate here).
>>
>> 3.  What format do I use to put in pps nanoseconds compensation for 
>> cable delay (I use about 19 feet of RG-58U).  I understand this 
>> should be a negative number.
>>
>> 4.  Does anyone know a way to force the 5335A counter to display 
>> another decimal place in frequency measurements?  I am getting to 
>> 0.001 Hz by using the "mean of 100 counts" function on the counter, 
>> but I think the counter has at least one more digit available which I 
>> would like to use when accuracy justifies it (e.g. when using the 
>> TBolt as an external time source).
>>
>> Any comments and suggestions appreciated
>> Jim, KF7A
>>
>>
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