[time-nuts] Early Christmas - DMTD up and running

[Skip Withrow]

Hello Time-Nuts,
Some time back Bert Kehren supplied me with a DMTD board that he and
Jeurig (in Germany) did.  Bert was kind enough to include the
transformers and mixers with the board that he sent.  This board is
quite similar to the Bill Wriley (Hamilton Technical Services) system,
and is just the dual mixer portion.  I have finally managed to acquire
all the rest of the parts, a 4.999990MHz oscillator, power supplies,
and packaged everything is a 2U chassis (first attached picture).

The system drives my HP 5370B (second attachment), which is obviously
overkill.  A TICC or modest counter with TI capability would be
sufficient. First tests are quite encouraging.  Right now I only have
5MHz capability, and will add a doubler to the other port of the
offset oscillator to give me 10MHz ability as well.  Even though
running a 5MHz input with a 10Hz offset gives you a 500,000 increase
in resolution, noise in the system will degrade performance.
However, it does look like my noise floor has been lowered by over two
orders of magnitude.  The 5370B can get you to about 1x10E-10 at 1sec,
with the DMTD it looks like it is about 7x10E-13 at 1 sec.  I now also
get data between .1 and 1 second with the DMTD.  The third attachment
is a timeLab plot of several different noise floor runs (and a couple
of other random tests).

This will bring the true performance of many systems out of the noise
for lower taus, and is necessary for high-performance oscillators.
I'm looking forward to having some fun.

Need to learn a lot more though.
1. I have a three-way comparison of three oscillators done on a
borrowed TSC-5110.  Need to make sure that the DMTD gives me similar
results.
2. Corby Dawson uses a very good crystal oscillator for short taus and
a maser for longer taus as the reference.  Need to figure out my best
reference for specific measurements.
3. I do have an HP 8660B synthesized generator.  I need to investigate
whether it may be a good offset oscillator candidate.  This would
allow different sample rates and measurement of oscillators at odd
frequencies (which I do have).

Thanks for the bandwidth to show-and-tell.

Regards,
Skip Withrow
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