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Old January 24th 07, 01:29 AM posted to sci.electronics.design,alt.engineering.electrical,rec.radio.amateur.antenna
Kaimbridge Kaimbridge is offline
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First recorded activity by RadioBanter: Jan 2007
Posts: 1
Default Converting From mV/m To Decayed mW (ERP)

I've seen the different conversions for mW, mV, mV/m, dBm, mostly based
on 50 ohms.
What I'm interested in is converting a given field strength mV/m, at a
given distance for a particular frequency, to the equivalent (decayed)
baseline wattage.
For instance, in section 73.318, the FCC defines the FM blanket
overload boundary as 562 mV/m (115 dBu), having a distance equalling
..394 * KW^.5 (ERP), where (I believe) ".394" is supposed to be
50000^.5/562.
So, assuming flat terrain with "raw reception" (meaning no antenna and
line gain/loss), what would the equivalent ERP wattage be (i.e., if you
took a field strength meter and held it next to a transmitter, what
would the wattage be to produce 562 mV/m?)?
Since wattge can be found from mV/m, what would the equation for
decayed wattage (mW_d) be, given an ERP (KW_erp), frequency (MHz) and
distance (Km)? Instead of 50, should 2*Pi*60 Hz (~=~ 377) be used for
ohms?

~Kaimbridge~

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