[ARC5] RF Ammeter Puzzle

[Bob Macklin]

The ARC-5 transmitters had the built in loading coils and the antenna
current meter was between the output terminal of the Tx and the antenna.

The large aircraft with the ART-13s had trailing wire antennas. But I never
worked on an ART-13 aircraft installation.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message ----- 
From: <sbjohnston at aol.com>
To: <jfor at quik.com>; <ARC5 at mailman.qth.net>
Sent: Wednesday, February 27, 2008 7:44 PM
Subject: Re: [ARC5] RF Ammeter Puzzle


>
> The ARC-5 was made for short wire antennas on aircraft, wasn't it?
> Those antennas would have quite low radiation resistance (which is the
> load that pulls the current detected by an RF ammeter).  The ART-13
> might have been designed for longer antennas with higher radiation
> resistances.  The lower the resistance, the greater the current, for
> the same power.
>
> For example, suppose the ARC-5 was used with an antenna with R=10 ohms.
>   50 watts of power would be about 2.24 amps.  The same 50 watts on a 50
> ohm antenna would be 1 amp.
>
> The formulas are P = I x I x R   or   I = SqRt(P/R)   etc
>
> Steve WD8DAS
>
>
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