Tag Archives: OSC 49-61C

HP 8566B Spectrum Analyzer: YTO/YTX tuning, flatness adjustment, and an OCXO

The 8566B I am dealing with here as parts from at least three units, so no wonder that the YTO/YTX drivers are all completely out of adjustment. So much that the LO sometimes locks on an incorrect multiple of the reference, or that it doesn’t lock at all.

Well, the adjustments are all well described in the manuals, rather straightforward.

8566b corr coeff
The amplitude offset at 10 Hz, a bit more than I want it to be, but this is related to the A4A7 assy of the 85662A, not to the 8566B itself.

8568b flatness adjusted
Might still tweak it a little bit, when all repairs are complete, but for now, a quite satisfactory result.

The OCXO, it is mounted in a set of 3 rubber isolators, here are the rough dimensions, if you want to fit a custom OCXO….
0960-0477-1 osc 49-61c dimensions

8566b 0960-0477-1 osc 49-61C 10 mhz ocxo

From the service manual – there are at least two versions of the 8566B, one using the HP 10811, and the other, using an Ovenaire OSC 49-61C.
8566b a22 assy ocxo

As far as I know, the oscillators have more or less the same performance level, but the connectors on the motherboard are different (still carrying the same voltages – the 10811 has small add-on regular board, 5062-1909), and there may be also differences in the holding brackets.
5062-1909 10811-60111 board
Notice the different plug! I have a spare 8568B motherboard around that supports this connector style.

One of the many test results, the 22 GHz noise floor.
8566b baseline noise 22 ghz

Not bad at all, about -118 dBm. Also checked the power line spurs and the noise characteristics, all considerably better than specified.
The only downside: total weight, of the 8568B: 112 lbs, and two strong fans.