[ntp:questions] Dual Mixer Time Difference (DMTD) instruments sought
David L. Mills
mills at udel.edu
Tue May 13 05:26:49 UTC 2008
Joseph,
I took a look at the instrument instruction manual to see what is going
on. In typical todayspeak, Symmetricom doesn't say how the gadget works.
I make it what used to be called a Costas direct-conversion receiver.
The test signal is connected to two mixers; the reference oscillator is
connected to the other mixer inputs in quadrature. The mixer outputs are
digitized and filtered, the Q signal is shifted 90 degrees from the I
signal and combinted. The result is a baseband SSB dignal which is then
Fourier transformed for display. Is this what you have in mind?
Dave
Joseph Gwinn wrote:
> In article <joegwinn-01533B.10412407052008 at comcast.dca.giganews.com>,
> Joseph Gwinn <joegwinn at comcast.net> wrote:
>
>
>>I may need a Dual Mixer Time Difference (DMTD) instrument, to measure
>>picosecond changes in electrical length in a coax plus amplifier time
>>reference signal distribution system with total delays in the hundreds
>>of nanoseconds, currently operating at 10 MHz (sinewave), but with 100
>>MHz likely at some future date.
>>
>>What DMTD instruments are commercially available? A google search was
>>not successful - all noise no detectable signal, probably because DMTD
>>instruments are not that common, and many people build their own.
>
>
> The silence, the silence. I have not found too many commercial DMTF
> units, but I have found one, although the maker does not market it a
> such:
>
> The Symmetricom 5120
> <http://www.symmttm.com/products_pn_adev_test_sets_5120A.asp> is at
> heart a digital DMTD instrument, and will make all the usual DMTD
> measurements, although it is marketed primarily as a phase noise test
> set.
>
> What else is available?
>
>
> Joe Gwinn
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