Simple tracking generator for HP8562A Spectrum Analyser

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.

 

Leave a Reply

Your email address will not be published. Required fields are marked *