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An update.

The Avantek YTO requires a lot more current to tune to the required frequencies than the HP YTO it replaces.? I was running into trouble because I was actually measuring the 2nd harmonic, which explained why it showed weak on the bench 8566A.? I was seeing minus some odd dBm where I would expect the 1st LO output should be around +10 dBm.? This is why I was having difficulties.? I needed to look lower in frequency than I thought for the strongest output.

Tho get the Avantek to run at the needed frequencies required some circuit modifications.

Bottom line, it required adding some extra resistors in parallel to the current sense resistors in the Q301 and Q302 circuits.? In each case, the two parallel 100 ohm resistors had to have added two each precision 76.8 ohm low TC resistors.? This moved the 50 ohm sense resistor to 21.72 ohms.? Once this was done, I was able to get the YTO tuning alignment completed successfully at 3.200 and 6.050 GHz per the manual.

The Avantek main coil is 10 ohms while the HP coil was 39 ohms.? To limit dissipation in the drive transistors and sense resistors, I added a 20 ohm 5 watt resistor in series with the main coil, at the YTO.? At the 305 mA required at 6.050 GHz, it dissipates 1.8 watts. The power dissipation in components is calculated to be within limits.

The analyzer errors disappeared and I can work further on it.

I did notice that the drive transistor for the YTF is running VERY hot.? I will need to look into that.

Peter