Paul,
We just want to help you with that curiosity, it sounds like a fun
little project. :)
The FRS-C [1] has a range of +/- 1E-9 over 0-5V, so EFC sensitivity is
4E-10/V.
The Z3801A has a range of 5.20E-10 [2] over -5V to +5V [3], so EFC
sensitivity is 5.2E-11/V.
So, it looks like you need to have a gain of 8 and raise the EFC 2.5 V.
Cheers,
Magnus
[1] http://www.to-way.com/tf/frs.pdf
[2] http://www.leapsecond.com/pages/z3801a-efc/
[3] http://www.realhamradio.com/joe-geller.htm
On 12/28/2016 11:42 PM, paul swed wrote:
Magnus and Bob,
Thank you for your response. As far as the original HO 10811 oscillator
goes there is some well written details on it behavior and sensitivity. It
was not the same as a standard 10811. A far smaller range as I recall. But
the data is there.
Its funny on the RB I have the EFC range from the spec sheet. It really
tunes from 0-5V. But I find it interesting that the best alignment with
other references is sub 1V. Its an old FRS C and I have others that may
present a more centered range.
I'll have to compare the detials that I have on the 10811 and FRS C. But I
actually pulled out a 100:1 antenuator I was using on the Piezo crystal
that indeed does lock.
Goal in all of this is nothing special simply curiosity.
Thanks again. When I have some real numbers to share I will.
Regards
Paul
WB8TSL
On Tue, Dec 27, 2016 at 10:26 PM, Bob Camp <[email protected]> wrote:
Hi
The loop gain (as Magnus mentions) needs to be “correct” for the Rb. Since
the firmware was written for an OCXO with a PPM(ish) trim range, tacking it
on to a PPB(ish) Rb will require everything to scale by 1000:1. That’s 10
bits.
You may (or may not) have enough resolution in the math to handle that wide
a range of gains.
If it really locks, the next challenge is to get it to run out to ~ 4 days
or more on
the loop. Again, the firmware may or may not be able to do this. Unless it
does,
the Rb really will not lock as well as it could.
With the Rb correctly locked, you still have the issue that the Rb is a
2x10^-11
device (ADEV) at 1 second and the OCXO probably is 2x10^-12 (or better).
For
driving a counter with a normal gate, the Rb may not show much (if any)
improvement.
There is the slight chance the ADEV will get the firmware confused…..
Since the firmware source is running around somewhere, you *could* dig into
all of this wonderful stuff :)
Bob
On Dec 27, 2016, at 8:33 PM, paul swed <[email protected]> wrote:
OK so could not resist. The replacement of the HP 10811 with a PIEZO ocxo
went very well. So in for a penny in for a pound. Why not an RB. Having a
few around. Choice efratom FRS-c. Lot of thought went into this choice.
Not
really it was there. It has a inverse frequency to EFC voltage just like
the piezo and opposite the HP 10811.
Well it connects runs and locks using the simple 1 opamp level ofset and
and phase inverter.
But locked is a funny comment. According to HPsatstat and LH. Its pll is
locked. But both scope and the LH graph shows a very slow frequency drift
that with the offset I can make positive or negative. A cycle at 10 ns
takes quite some time about an hour compared to a TBolt and another non
modified Z3801. At this level of resolution some things start to become
questionable.
I almost wonder if the modified z3801 under some level of drift assumes
everything is locked and fine. Can it be pushed beyond expectations. I
suspect it can.
Anyhow as I say a bit of GPSDO fun.
Regards
Paul
WB8TSL
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