[time-nuts] Newbie questions

Tom Duckworth tomduck at comcast.net
Tue Jan 5 19:45:17 UTC 2010


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
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Osc meas-calib.pdf
Type: application/pdf
Size: 50919 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/time-nuts/attachments/20100105/c90d9a15/attachment-0001.pdf>


More information about the time-nuts mailing list