I said no *manufacturer* does it this way. NBS is not
a manufacturer. In a one-off money-is-no-object non-portable
standard, you can make direct multiplication work. It
will not work well in a 5061, because of RF leakage
issues specific to the 5061 that are well documented.
Bolting on a different synthesizer does nothing to change that.
The decision not to use direct multiplication has nothing to
do with not being able to figure out how to synthesize the
correct frequency. Certainly by the time we did the 5071A,
we were already using DDS, and it wouldn't have been any
problem to synthesize for direct multiplication if we had
wanted to do that. You seem to be doing it the hard way
(pre DDS) involving Diophantine equations. So it's easier
to do direct multiply than it used to be, but that doesn't
necessarily mean you should do it that way.
Rick
On 6/2/2017 10:59 AM, Donald E. Pauly wrote:
https://www.febo.com/pipermail/time-nuts/2017-May/105566.html
A guy by the name of David W. Allan used direct multiplication to
build NBS-4 and NBS-5, see http://tf.nist.gov/general/pdf/65.pdf . He
didn't see anything wrong with it. He used a commercial frequency
standard modified from 5 mc to 5.006880 mc. That in turn was
multiplied by 1836. This was a multiplier chain of 2·2·3·3·3·17.
When multiplied to 9192 mc, this is 90 cycles low so the standard
would be forced high by 0.05 cps.. They measured the locked frequency
standard to determine the actual frequency of the cesium line. I
propose NO multiplier chain.
What are the supposed problems in using a direct submultiple of the
cesium resonance? It seems to me that all other techniques result in
more phase noise there. I found the relationship 91.92631770
mc·(137,075/126,008)=99,999,999.98992 cps=100,000.000--0.01008 cps.
It is low by 0.1 ppb and therefore cannot be adjusted by C field
current. The C field can only lower the frequency. There is another
relationship that gives a higher frequency of a fraction of a part per
billion which is easily adjustable. Perhaps HP was unaware that such
a frequency exists.
πθ°μΩω±√·Γλ
WB0KV
---------- Forwarded message ----------
From: Richard (Rick) Karlquist <rich...@karlquist.com>
Date: Thu, Jun 1, 2017 at 10:01 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>, "Donald E. Pauly" <trojancow...@gmail.com>,
"rwa...@aol.com" <rwa...@aol.com>
Direct multiplication to 9192 MHz isn't used
by any manufacturer of any atomic clock that I
know of, due to its well known disadvantages.
I can state for a fact that it was summarily
rejected by the designers of the 5060/5061
(Cutler, et al). In the 5071, I (being the
RF designer) also summarily rejected it.
The architecture that is instead used is indeed
complex and expensive as you say. It is
also ACCURATE.
Rick
On 6/1/2017 7:04 PM, Donald E. Pauly wrote:
https://www.febo.com/pipermail/time-nuts/2017-May/105566.html
The lock system on the HP5071 is complex and expensive. My plan to
improve the HP5061B is to to use a pair of third overtone crystals
running at 91.9 mc and 100 mc. I have come up with the magic numbers
to lock them together. This eliminates all multipliers with the
exception of the A4 board. The 12.61 mc synthesizer input presently
wastes half the microwave power produced by the 90 mc input in the
unused lower sideband. Therefore only half the 91.9 mc drive is
required.
Eight bit ECL dividers in one package are available to perform the
necessary lock. When multiplied by 100 to the cesium resonance line,
the 91.9 mc frequency is a few cycles high so that C field currents
are reasonable. With crystal cuts for zero temperature coefficient at
25°C, it is possible to get along without an oven. Room temperature
performance at 25°C±5°C is ±15·10^-9. Oscillator warm up time would
be measured in seconds.
Square wave modulation of variable frequency and amplitude shows
promise for reducing the noise effects of the beam tube. You can
smoothly change the lock time constant, deviation and frequency. This
would avoid the big disturbance of the HP5061B when you switch from
OPR to LTC. (OPR=operate with 1 second time constant, LTC=operate with
100 second time constant)
πθ°μΩω±√·Γλ
WB0KV
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