[time-nuts] Neat toys on eBay for PN measurement

John Miles jmiles at pop.net
Tue Jul 3 23:55:59 EDT 2007

There are a couple of near-mint-looking HP 11729C carrier noise test sets on
eBay right now.  They are sold by nouturnhere, a great seller in my
experience.  They have the AM noise detection option (130) and all of the
available filters from 5 MHz to 18 GHz.

Basically this is a general-purpose microwave downconverter whose LO uses
harmonics of the 640-MHz reference output from an 8662A/8663A to downconvert
the signal to be measured to a frequency below 1280 MHz, where it is then
mixed down to a baseband IF with the same 8662A's output.  An 8662A is not
mandatory, but it's convenient because it can provide both LOs at once.

The baseband IF is high-pass filtered at 10 Hz to get rid of the DC
component, amplified by 40 dB with a 1.6-dB LNA, and fed to a spectrum
analyzer for noise measurement.  There is also a general-purpose PLL that
can be used to maintain phase quadrature.  A good description of the whole
thing is in this app note:


There are two units left right now.  I have no idea of $969 BIN is a good
price or not, but they are rare enough, especially in this condition, that I
thought it was worth snagging one.  If it turns out to be in good shape, I
will add the necessary GPIB and user-interface code to PN.EXE to allow it to
work with any of the spectrum analyzers currently supported.

The system noise floor with one of these is not as good as a Wavecrest box
for low-frequency carrier measurement, but it is much better than a spectrum
analyzer by itself, and hey, it goes to 18 GHz, right?

-- john, KE5FX

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