[AMRadio] OT: FCC pronouncement on I2R power measurement?


sbjohnston at aol.com sbjohnston at aol.com
Thu Aug 5 13:25:01 EDT 2010


?
>Can anyone here point me to written evidence that FCC accepted an I sq 
R
>power measurement at the antenna for AM bc licence compliance,
>within a range of +/- 2% certainty.

There are two defined ways to measure power of a AM broadcast station 
in the U.S.  The antenna current squared times antenna resistance would 
be one way to do the "direct method" .  The "indirect method" is final 
stage input voltage X final stage input current times published final 
stage efficiency for the transmitter.     See FCC  §  73.51

>Delta developed their CPB-1 bridge specifically to determine
>power levels to the satisfaction of FCC

The Delta CPB-1 is an operating impedance bridge - not a power meter.  
It would be used to determine the impedance of the input of an antenna 
system and thus reveal the resistance of the antenna system - the "R" 
in P=IsquaredR.   Are you thinking of the Delta line of antenna current 
meters?  They are sampler/amplifiers meant to respond like a 
thermocouple ammeter but not actually be in the circuit.  It is still 
the direct method.

>disputes with stations could not be easily resolved with power meters 
such as Bird now offer.

A Bird wattmeter would not be an acceptable device for measuring the 
power of an AM broadcast station in the US.

Steve

sbjohnston at aol.com
http://www.wd8das.net/
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-----Original Message-----
From: Nigel Holmes <Holmes.Nigel at abc.net.au>
To: Discussion of AM Radio in the Amateur Service 
<amradio at mailman.qth.net>
Sent: Thu, Aug 5, 2010 3:01 am
Subject: [AMRadio] OT: FCC pronouncement on I2R power measurement?


Perhaps OT although it relates to AM bc transmitters...

Can anyone here point me to written evidence that FCC accepted an I 
squared R
power measurement at the antenna for evidence of AM bc licence 
compliance,
within a range of +/- 2% certainty.

Delta developed their CPB-1 bridge specifically to determine power 
levels to the
satisfaction of FCC in the days when disputes with stations could not 
be easily
resolved with power meters such as Bird now offer.  FCC must have made 
some
pronouncements on the method.

73  Nigel VK3DZ
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