[time-nuts] DMTD Terminations II

[Brian Kirby]

I got to correspond with a person at NIST today about DMTD - about the 
HP 10514B Mixers.  They pointed me to a application note at 
http://www.thegleam.com/ke5fx/stellex/5952-8217.pdf (hey - thats one of 
our time-nuts!) that shows driving the 10514 mixer at +13 dbm for the LO 
port and 0 dbm for the RF port.

This application note is a good read.  HP recommends terminating the 
mixer into a 3900 pF cap and 50 ohms in series for the RF termination.  
ANd they use a LC filter for their VNA set for 90 Khz.   I also looked 
at the schematic of the 8407A were I got the mixers from.  They 
terminate the IF into a 1100 pf cap in series with a 51 ohm resistor, 
and then it passes thru a 2.7 uH choke going into an amplifier - the IF 
I beleive is 298 Khz for this unit.

I also did a reconfiguration of my temporary DMTD experiment that has 
also improved the noise floor.  Drawing attached.  Also changed the 
drive levels.

For reference the previous configuration showed 2x10-11 for 0.1 sec; 
2x10-12 for 1 sec, 5x10-13 for 10 sec, 6x10-14 for 100 sec, 7x10-15 for 
1000 sec. for the noise floor.

The current configuration (of the drawing attached) shows 8x10-12 for 
0.1 sec; 8x10-13 for 1 sec, 8x10-14 for 10 sec, 8x10-15 for 100 sec and 
8x10-16 for 1000 sec.  I used a little more attention in sheilding and 
spacing to eliminate crosstalk.  Note the noise shows some linearity 
this time....plus more drive....

Brian - KD4FM




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