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

Fri Jan 7 03:29:13 UTC 2005

My 4060 was working like that for a while, but eventially the green
light wouldn't light anymore.  What I found was the OCXO had aged to
a point where its frequency could no longer be dragged back to the
proper frequency with the voltage control.  I know there is an adjustment
available inside the oven, but I never got around to finding and fixing
it.  (anyone know how to adjust the crystal osc. without ripping it
completely apart?)

-Chuck Harris

Brooke Clarke wrote:
> 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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>>  
>>
>>
>>  
>>
> 