I looked again and still don't see anything that suggests that it
either has an analog input or is intended for use with audio signals.
Where are you getting this information? Or do you have one and you're
actually using it in this manner. I don't even see a place to connect a
coil (I assumed it was internal) but then they really don't show very
much on the web site. If you have a link to an instruction manual or a
good picture that shows the connectors, please pass it along.

I could very well be wrong but I don't see any evidence that it can be
used in the way you suggest, other than perhaps with some modification.
That's cheating!

Ok so for all folks who have tomatos on the eyes a STEP by STEP
instruction ;-)
Go to
http://test1.contenttest.net/Spektru...sator_en.shtml
Go to "SPECTRAN NF-3020". There it says " This extended version of the
SPECTRAN NF-3010 also allows analysis of EXTERNAL signal sources via
its SMA input.".
Or click "COMPLETE description". In the NEW window you can see in the
"Overview of features SPECTRAN® LF spectrum analysers" under "
INTERFACES" the feature "External signal input (screened SMA input)".
Got it?
With the SMA input you can feed what ever you want. Its like a SCOPE!