[600MRG] Definition needed - V/m

[sbjohnston at aol.com]

I think the scientific definition is the field produced when a certain voltage is applied between two infinite parallel planes spaced one meter apart. For example, a field strength of 1 V/m is achieved if a voltage of 1 V is applied between two infinite parallel planes spaced 1 m apart. 

Radio signal field strength is usually measured by the voltage or power induced onto a standard antenna measured on a calibrated detector/meter.  For measurements out in the real world, a receiver with a signal level meter is used.  

It can read out directly in volts per meter or in dBμV/m (the signal strength relative to 1 microvolt per meter.)
 
mV/m = 10(dBu/20)  / 1000.     dBu = 20 log10 ((mV/m) * 1000.)

	 	 The factor of 1000 is used to convert millivolts per meter to microvolts per meter.

Potomac Instruments makes the most commonly used line of field strength meter for broadcast stations - here are some:

http://www.pi-usa.com/legacyProducts.htm

I've used the Potomac FIMs and the earlier RCA or Nems-Clarke tube-type units my whole career.

http://www.americanradiohistory.com/Archive-Catalogs/RCA-1950/Test-and-Measure-RCA-1950-Broadcast-Catalog-6.pdf

The cover contains a shielded loop.  The meter is calibrated by exposing it to a standard field and adjusting the gain.



Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
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