[time-nuts] HP 11729C versus 11848A

Adrian rfnuts at arcor.de
Sat May 8 05:38:29 UTC 2010

Just the roughly 16 dB of insertion loss caused by the 562 ohm resistor 
at the input don't make that filter such a great solution ;-)
So, I brewed something better together...
The 10 kHz beat note is now near 0 dBm when the R input signal is 
decreased by 40 dB, which makes a lot more sense than before...
And, I have a noise floor of some -165 to -169 dBc/Hz at +7.5 dBm input, 
and I'm seeing the 10811A's some 5 dB above that.


John Miles schrieb:
>> John,
>> I'd say you nailed it.
>> After some more testing, I can confirm that the limiter amp and the LPF
>> are the culprit.
>> I opened the box and plugged directly into the mixer LO port.
>> And, for the LPF, as a quick 'n dirty solution, I connected the <1 MHz
>> front panel output with the LNA input.
>> Now, at 10 dBm each into the mixer ports, I'm getting a noise floor of
>> <-145 dBc/Hz at 100 Hz and about -170 dBc/Hz at 10 kHz and above.
> That's pretty aggressive for 10811s.  The floor on those is usually
> around -165 dBc/Hz.  How's your calibration process -- are you accounting
> for the 600 ohm output Z of the <1 MHz output port?  It'll lose a few dB if
> you try to drive 50 ohms with it, and/or the filter response won't be
> correct.
> -- john, KE5FX
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