My previous post described a simple cable change that switches the VNA range to 1-2 GHz. I should have mentioned that the same thing works in spectrum analyzer mode, sort of.

With the Mixer 1 output run to the IF2 Amp, we are looking for Mixer 1 to produce a 10.7 MHz IF signal. Mixer 1 will thus detect any signal that differs from LO1 by 10.7 MHz. LO1 ranges roughly from 1-2 GHz, which gives us a 1-2 GHz detection range.

The catch is that Mixer 1 will detect a signal when it is 10.7 MHz above LO1, and as LO1 increases during the sweep it will detect the same signal again when it becomes 10.7 MHz below LO1. That means every signal will get graphed twice, as though the true spectrum is overlaid with another copy (the "image") shifted 21.4 MHz.

Maybe this image is a problem and maybe not. If you are looking at a 1.5 GHz oscillator signal, or a harmonic of 500 MHz, the image is easy to recognize/ignore and you can go about your business. Or narrow the scan so the image is off the screen. On the other hand, if you want to look at a crowded area of spectrum spanning more than 21.4 MHz, the duplicate image may create confusion.

So the 1-2 GHz SA is not suitable for all purposes, but it is for many. Not bad for just moving a cable.

(There is also a way for the SA to cover from 2-3 GHz (subject to whatever the limit of the ADE-11X turns out to be), without even having to make a cable change. But that's a different topic.)

Sam W.