Fred Bloggs hath wroth:
I've used Narda survey meters for measuring broadcast transmitter field strength and mountain top radio site safety limits.
I've never dived inside to see how they work because I didn't want to wreck the calibration.
I didn't think they were that crude. Not all probes use thermistors. The EMR-300 series uses diode detectors.
However, I wasn't trying to turn a microwave leakage detector into an RF field survey instrument. What I was looking for is something upon which to build a 2.4 GHz RF signal strength meter suitable for direction finding (or sniffing) for sources of non-802.11 interference. The problem with the typical "hot spot finder" is that they only detect 802.11 signals, and are set to ignore everything else. I ended up with an abomination something like this:
but with a proper PCB, a tiny microwave diode instead of a WWII antique, a proper horn antenna, a 2.4GHz bandpass filter, and some local DC gain. I would post a picture but there's not much to see.