[time-nuts] DMTD Terminations II
kilodelta4foxmike at gmail.com
Wed Mar 3 04:28:15 UTC 2010
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
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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