"Sal M. Onella" wrote in
:

I've never had a spectrum analyzer measure field strength directly,
although maybe the Test & Measurement science is getting close. The
missing link is "antenna factor" (AF) which accounts for the db gain,
usually negative, for the antenna you're using. In my experience,

There are both EMC receivers and Spectrum Analysers intended for field
strength measurement, and modern digital system allow the antenna
response to be stored in the instrument and field strength automatically
calculated for different freqencies.

My FSM software (http://www.vk1od.net/fsm/) which is designed for making
field strength measurments using a conventional SSB comms receiver, an
antenna, a known attenuator, and a PC. FSM can read a file of Antenna
Factor vs Frequency and calculate a spline interpolation for the
frequency of measurement to (along with other factors) calculate the
received field strength in dBuV/m. I would be very surprised if any
modern digital instruments don't do likewise, either directly in the
instrument or in PC based analysis software, though there is a great
advantage in indication of field strength directly on the instrument.

In a recent test, the radiocomms regulator here loaded such a table of
modelled AF for an untuned loop antenna system
(http://www.vk1od.net/SmallUntunedSquareLoop/ssulNEC.htm) into a R&S EMC
receiver and made swept measurements using the loop over HF, and compared
them to the results from measurements using a R&S active loop (AF about
20dB lower than the passive loop). The difference of the medians was less
than a dB which speaks well for the NEC model!

Field strength is a bit of black magic to most hams.

Owen