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

Fri Jan 7 02:23:20 UTC 2005

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

-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com