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

Brooke Clarke brooke at pacific.net
Thu Jan 6 22:11:28 EST 2005


Hi Tom:

I think the Cs source is working OK.  I set the screwdriver coarse OCXO 
frequency to 9 nines with the loop open and the control voltage set for 
mid scale.  Then close the loop and force an automatic align which 
searches the control voltage while looking for a major beam current peak 
with about equal value valleys on either side.  It finds this in less 
than a minute and the Green Lock LED turns on.  The control voltage is 
very close to mid scale.

I think it may be a problem with how I've setup the 620 counter.  Need 
to read up on the Gate/Arm function.

73,

Brooke

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
>
>
>
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>
>  
>
>
>  
>

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