How do you measure electric field strength with an antenna and spectrum analyzer?
Use E=AF*V where E is the field strength in volts/meter, V is the voltage received by the spectrum analyzer, and AF is the antenna factor. The units of AF are 1/meter. The antenna factor is antenna specific and is supplied by the manufacturer.
E=AF*V in dB's becomes E(dBV/m)= AF(dB)/m + V(dB).
For example, if the voltage received is -30 dBV and the AF is 10 dB/m, then E is -20 dBV/m.