On Wed, 19 Sep 2007 00:17:53 GMT, Joerg
wrote:

John Larkin wrote:

I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.


Looks like a luxury analyzer. Aeroflex? I thought you could buy those
only with a GSA account or for government contract work.


It's the new 3 GHz Aeroflex; anybody can buy it. With all the options
(tracking gen, preamp, high resolution) it was $13K or something. It
has a few firmware bugs, but I think they're sincere about fixing
them. Except for a few glitches, it's a lovely box, with a beautiful
display.

I was disappointed in the harmonic distortion, -65 dB typically, but
it looks like that's actually not real bad compared to other units. We
have some RF signal generators that have THD numbers like 1.5%!

To test some amps we're doing, I guess we'll have to buy a few sets of
matched lowpass/highpass filters, so we can pump in a clean sinewave,
then and pull out the fundamental before we feed it to the spectrum
analyzer. What a nuisance. Maybe we should find/make a couple of
tunable notch filters.

How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?

Why don't spectrum analyzers do log sweeps?

John