492BP external mixer ident issue


Edward Prest
 

I have a new to me an external diplexer and a (home brew) mixer for 18G to 26GHz. I see up to 30db carrier over the noise floor signals with this setup. I see 8 harmonic signals including the expected cw signal at 24.3GHz. But I cant identify any of the signals using the built in ident feature. All I see is either the signal centered or base noise level as it alternates the IF back and forth. I should get one signal that stays on center frequency. I have tried all visible harmonics with no success.

There are no system errors reported, it auto cals. fine and works properly on bands 1,2,and 5.

This is for a 492BP sw v9.1. I know older units have to be set to only 500kHz / div span. No joy.

Any ideas whats wrong?


Edward Prest
 

Sort of working - but badly. As a test I tried injecting a sq wave from a cheapo chinese VNA, into the mixer port of the external diplexer, now I see groups of energy peaks pretty much as expected on the upper normal trace but on the lower ident trace I can only see a tiny right shifted version. At least the sw and hw is shifting the signal but why so much lower? ...and there is still nothing but noise on the lower ident trace with a real cw signal.

I would have thought the level would not change in ident mode. Zoomed out to max span it all looks even enough. Ideas anyone? (...chirping of crickets...)


Edward Prest
 

The solution to the misbehaving Ident mode is to allow the SA to warm up fully for an hour. The mode gets better as it warms up, its not a sudden thing.

I don't know why the alternate display is sensitive to temp. In Ident mode both first and second IF's are moved equally and then by some factor related to the harmonic for the center frequency selected - but who knows the exact algorithm. Its only the shifted display in Ident mode that disappears until warm.