Erik,

About a year ago my garage door remote quit working. I traced the source to be a faulty switch. After repairing it, I wanted to look at the transmitted rf signal. I WAG'd that I could use some PCB 'Blue Wire' to wind a loop antenna and observe the potential induced in the loop from a B-field emanating from the remote. It worked. Even though the DSO I had available at the time had a lower bandwidth than the transmitted signal, it showed the transmitted bit pattern as a blur on the screen.

Now, given an observable signal, I suppose I could calculate an aggregate B-field strength based on the number of loop turns and loop area. Further, if I were to make the loop area 'small enough' I could map the volume around the garage door opener and determine in a finite element sense the field pattern emanating from the circuit - maybe even get a sense as to the location on the pcb from which the field is radiating.

Granted there is no frequency selectivity in what I did, but selectivity and a well-calibrated antenna is all we get when we go into an anechoic chamber or OATS for EMC tests.

To summarize, when (not if) I have difficulty with a circuit for which I've exhausted the most likely prospects I think I'll wind a loop to 'sniff out' potential EMI.

Hope it works for you, too.

Bruce