HP 8360 Signal Generators 20GHz to 26.5GHz

[jjoonathan]

I have another round of notes I'd like to share in partially complete form because I've been asked for them a few times and maybe if I put them in a central place I can iterate them into shape. Also, the pictures are fun 

Q: Can I turn a 20GHz 8360 into a 26.5GHz 8360?

A: Yes, but you're going to work for it.

Step 1: unlock cal constants 700-703 by clearing the RAM, grabbing the EEPROM with a programmer, finding cal constant 700 (serial number, matches the back of the instrument), and setting it to 0. This will invalidate the EEPROM checksum and if you failed to clear the RAM the RAM constants will win because they still have a good checksum, undoing your work. But if you cleared the RAM, the instrument will begrudgingly accept the constants with the bad checksum, which you should immediately turn around and write back to the EEPROM in order to make the checksum good again. Now that the serial number is 0 it's back in factory mode and cal constants 700-703 are unlocked.

Step 2: change constant 702 Stop Freq Limit from 2000 to 2650. Write the EEPROM. Now Band 4 is unlocked.

Step 3: calibrate to maximize amplitude across Band 4. There are YTM and YTF slope/gain constants in the EEPROM, but the core difficulty is not in adjusting these constants but rather in adjusting the potentiometers on the Dual Ball Driver board to fit the YIG curves. I attached an otherwise unrelated example of such a curve, which begins going nonlinear at a higher frequency than the YTM and YTF in an 8360 but shows what you are up against and why in the top band you can't simply fit the slope/gain and call it a day, even though that works in the lower bands. I have been meaning to make a video on this some time but haven't gotten around to it.

Step 4: if you want to meet amplitude spec, replace the 5086-7616 FILTER with a 5086-7623 AMP-FILTER. The difference is, well, another amplifier in the signal chain that is important for meeting spec. See measurements and pictures below.

Step 5: do an amplitude calibration. See "cal_lvl_325.ipynb" in https://github.com/jjoonathan/cal-8360-sig-gen

[guagg]

good job

[BillyO]

Q: Why would you turn a 20GHz 8360 into a 26.5GHz 8360?

A: Because I can.

And that folks, is a perfectly reasonable reason.

Kudos!

[KE5FX]

Are there battery-backed RAMs in these things that hold the cal constants?  I didn't know that, if so.  Should probably deal with it in my own unit PDQ.