[time-nuts] FTS4060/S24 Location of E26 Test Point & ConfirmOperation?

Fri Jan 7 09:13:21 EST 2005

Brooke, I'd double check the triggering.  In the couple of times I've 
tried to do time interval with 1pps on one input and a higher frequency 
on the other, I've noted similar problems.  It may be that you're 
stopping or starting on a different cycle of the high frequency due to 
dead time in the counter or some other mechanism I haven't figured out.

Not sure that's the problem, but it might be worth checking.  If you can 
come up with an external divider to 1pps you can eliminate that source 
of potential error (and possibly add some new ones... :-) ).

John
----

Tom Van Baak wrote:
> Ouch. That's a pretty large frequency error. In your
> previous example it looked like it was much less than
> 0.1 ns / s. Did I misunderstand your earlier results?
> 
> No, you can't adjust a frequency error that large with
> the C-field. The C-field is intended to make small
> corrections for things like changes in ambient
> magnetic field or gravitational corrections for altitude
> or time scale frequency steering. It's only a 3 digit
> thumbwheel with LSD resolution of 2e-14 so the
> maximum range is 2e-11.
> 
> 1 ns / s is OCXO territory.
> 
> /tvb
> 
>   ----- Original Message ----- 
>   From: Brooke Clarke 
>   To: Tom Van Baak ; Discussion of precise time and frequency measurement 
>   Sent: Thursday, January 06, 2005 18:00
>   Subject: Re: [time-nuts] FTS4060/S24 Location of E26 Test Point & ConfirmOperation?
> 
> 
>   Hi Tom:
> 
>   If the 620 counter is set into TI mode, trigger on A (PRS10 1 PPS) and B is the 1 MHz FTS4060 1 MHz output then,
>   the count is something like 23.xxx ns, but it keeps rising at about 1 ns per second of clock time.
>   For example at 5:54:00  105.486 ns
>   at 5:55:00  156.510
> 
>   (156.510 - 105.486) ns / 60 seconds = 8.5E-10
>   at 5:57:00 it's 260.178 ns
> 
>   (260.178 - 105.486) ns / 180 sec = 8.594 E-10
> 
>   at 5:59:00 it's 361.559 ns
>   (361.559 - 105.486) ns / 300 = 8.5357 E-10
> 
>   So does that mean I need to adjust the C field?
> 
>   Brooke
> 
>   Tom Van Baak wrote:
> 
> (2) I'm trying to come up with some way to see if it's really working.  I
> have a SR620 Time Interval counter using the 10 MHz output output from the
> SR PRS10 as it's reference.  I have the 1 PPS from the PRS10 connected to
> the A input and the 1 MHz output from the 4060 connected to the B input.
> The counter is set for TI mode trigger on B and average 10 readings.  The
> idea is that the rising
>     
> 
> Perfect. when there is no 1 PPS output this is a good
> way to do it. Unless there is a large frequency offset,
> using the rising edge of a 1 MHz output is essentially
> the same as using a 1 PPS output. A frequency error
> of 1 ppm is 1 us per second; an error of 1 ppb is 1 us
> per 1000 seconds. So this method is worthless when
> the frequency error is in the ppm range (it wraps too
> frequently) but will works well near 1 ppb or better.
> 
>   
> The display shows .9936202, .993630, .993601 i.e. there is some change at
> the 10 micro second digit, this seems to be wrong, maybe there should be
> change at the 10 ns digit.  What am I doing wrong?
>     
> 
> The TI you expect will be a value between 0 and the
> maximum possible period of a 1 MHz signal, or 1 us.
> What scale is being displayed? I would guess the
> three numbers you gave are microsecond units:
>     0.993 6202
>     0.993 639
>     0.993 601
> meaning the TI is stable to 0.1 ns = 100 ps. If this
> keeps up for even 10 readings you're already looking
> at 1e-11 frequency stability so I would say your
> FTS 4060 is clearly locked.
> 
>   
> Measuring the FTS4060 frequency gives: 9,999,999.99278, .99368, .99239
> i.e. a jitter Allan variance of about 12 milli Hz or parts in 10^10 or not
> as good as I would hope.
>     
> 
> What was the gate time for these measurements?
> Remember the reported jitter is the RMS sum of
> the PRS10 jitter, the counter trigger jitter, the counter
> external timebase phase lock jitter, and the FTS
> 4060 jitter.
> 
> Use a 10 or 100 second gate and a stat count of
> at least 10 and let us know how much the jitter
> gets down to. I bet you get into uHz this way.
> 
>   
> The Green Lock LED has been on for 4 1/2 hours now.
> The 1 MHz output is still reading 999,999.99xxx  Hz.
>     
> 
> That's only 8 good digits; the x's worry me. I would
> expect you get at least 10 good digits and a few x's.
> 
> Just for fun, check the 10 MHz output also. Some
> frequency standards have pure 5/10 MHz outputs
> but the 1 MHz and 100 kHz outputs are made with
> cheap dividers and have more jitter and phase noise.
> 
>   
> How do I use the Zeeman input on a 4060?
>     
> 
> Put a 1 Vrms 40xxx kHz sinewave into the Zeeman
> input, open loop, and adjust the C-field knob/thumb
> reading for maximum signal. Then the 1 PPS output
> should be as close to marking the SI second as
> possible. The exact 40 kHz frequency to use should
> be written on the unit somewhere. Most people not
> set their Cs against daily averages of GPS but if you
> lived in a cave, the Zeeman input would be the way
> you tweak your Cs for maximum accuracy.
> 
> /tvb
> 
> 
> 
> _______________________________________________
> time-nuts mailing list
> time-nuts at febo.com
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> 
> 
>   
> 
> 