[time-nuts] HP 11729C versus 11848A

[John Miles]

That sounds about right to me.  I was guessing you meant 40 dB and not 30 dB
in the previous message, or there was something else causing about 10 dB of
loss.  Lots of things to go wrong in this process!

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Adrian
> Sent: Friday, May 07, 2010 10:38 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP 11729C versus 11848A
>
>
> 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.
>
> Adrian
>
>
> 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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