I’ve been trying out a simple tracking generator for 0-2700MHz to use with my HP8562A spectrum analyser. The plan is to use a 3910.7MHz signal from an ADF4351 locked to the same 10MHz ref as the 8562B, then mix it using a Minicircuits SIM-83+ to get the required 0-2700MHz baseband signal at about -10dBm.
This is the measured response of my 23cm LPF:
There are a few issues. Main one is that there is a fair bit of leakage of the signal as I don’t have it all boxed up, but it is at about -50dB, so not bad. There is also a bit of ripple every 180MHz or so, not sure what that is, could be the result of using only a 10kHz bandwidth, I need to get everything boxed up and screened and retested.
I took a spectrum of the fairly-flat output with no DUT using trace B, then took a trace A and did a subtraction. It was pretty much completely flat at 0dBm. Next, I inserted the filter and that resulted in the trace above.
Apart from the ripple, the curve of the LPF looks a reasonable facsimile of the manual curve I took previously http://www.g4dbn.uk/?p=323. OK, the scales are both different, but the bottom one took me 20 minutes, this is doing 20 scans per second…
I am fairly sure that it needs a decent 3-7GHz isolator (or isolation amplifier) and on the IF output from the 8562A to prevent the fundamental signal getting back in that way, and maybe a 3GHz HPF as well, but the principle looks good for baseband.
No time to do the testing at the next band up, other projects on the bench to finish first.