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e4406A with high spurs

Question asked by biff44 on Feb 29, 2012
Latest reply on Jun 10, 2014 by uprog
I picked up a used e4406a off of ebay.  Seemed to be working fairly well.  Downloaded the KE5FX phase noise utility and it works pretty well!  A nice cheap phase noise measurement system.

But, when testing it out I noticed some odd spurious outputs on the e4406A display.  At 640 MHz in, there was a spurious sideband displayed about 2.8 MHz higher than the carrier.  As I tuned the input frequency, the spur crossed over the carrier, so it acted like a N*LO -M*RF spur.  It was around 40 dBc down.

Oddly, it did not show up in the KE5FX acquisition phase noise plot!

Everything else in the VSA looks good.  Accurate power readings, etc.  I tried various sources, and checked on other spectrum analyzers, and the source does not have the spur.

So what inside of the E4406A is causing a spurious product like that?  Any suggestions, any way to cal something inside to remove it?  Or do I have a semi-blown front end?  

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