Some experimentation with the recently acquired 11729B test set: measuring the noise floor of a Giga-Tronics 605 synthesizer, running at about 7.2 GHz.

To do this, more than 250 pounds of equipment stacked up:

On top, the Giga-Tronics, in the middle, the 11729B, and below, the 8662A (providing the low noise 640 MHz carrier for the multiplier of the 11729B, and the variable LO to adjust the IF to the analyzer range).

Trying out two loop bandwidth on the 11729B, 10 Hz and 1 kHz. You can clearly see the loop impact on the measured noise:

Blue curve – 10 Hz BW setting
Green curve – 1 kHz BW setting

All spectra were recorded using a 3585A, and the KE5FX PN software (which is really great for all general phase noise measurement tasks).

The purple curve – this is when the FM modulation is switched on, at 0 amplitude – still, it introduces quite a bit of noise!