[time-nuts] DMTD Ideas

Brian Kirby kilodelta4foxmike at gmail.com
Fri Oct 2 01:17:31 UTC 2009

I have toyed with the idea of building a Dual Mixer Time Difference 
setup for testing oscillators.  I have attached a drawing I made and I 
have a few areas I need to clear up.

At Point #1 on the drawing (the output of the mixers) I expect to see 20 
mhz and the 100 hertz beat note.  My plans were to put a 3 db attenuator 
here and expecting it to provide a 20 mhz termination/match for the 20 
mhz part of the signal.  Do you think this would be an adequate way to 
terminate or does it need a better system ?

The Op Amps at Point #2 would be a something like LT1000s or so and they 
basically would only allow passing of the beat signal as they do not 
have the response to handle the 20 mhz signal.  They would have to have 
a lot of gain and also would simple RC low pass filter say for 120 hertz 
be good enough ?  The DBMs have 7 db conversion loss, the RF port goes 
into 1 db compression at +2 dbm.  The LO ports can take +13 dbm 
absolute, and are recommended drive at +7 dbm.  What voltage range can I 
expect out of the mixers (next question would be how much gain do the op 
amps need....).

At Point #3, I thought about using some type of Schmidt Trigger like a 
74AC14.  But is it necessary ?  The 5370B can be set to trigger from 
zero to 2 volts or so.

If the 5370B can see one shot performance of 20 pS (2x10-11 at one 
second) then a 100 hertz beat note should give 2x10-13 at 1 second, 
2x10-14 at 10 seconds, 2x10-15 at 100 seconds and so on.......correct ?

Brian - KD4FM
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