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!
In an effort to upgrade my phase noise measurement system, look what I found, for less than 1 cent, for the earlier list price in dollars: a quite amazing HP (Agilent, now: Keysight) 11729B, equipped with all bands from 0 to 18 GHz.
The 11729B works best with a 8662A generator, to supply a 640 MHz low noise signal, and a variable 0-1280 MHz to move the IF to the right position.
The 640 MHz low noise signal from the 8662A is filtered by a quite massive Wavetek filter, amplified to about 30 dBm (1 Watt), driving a HP 33004A-H18 comb generator. The right line is selected by a filter assembly, using multiple 18 GHz coax relais. HP did not save on parts here….
The “brain”, a MC68B09P, a trusty 8 bit CPU, or as Motorola calls it, a “Microprocessing Unit”.
Just in case you need it, the ROM file, stored on a 2764 EPROM. Version 2.1!