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[Amps] Question on Ameritron amp wattmeter circuit

To: <amps@contesting.com>
Subject: [Amps] Question on Ameritron amp wattmeter circuit
From: G3SEK at ifwtech.co.uk (Ian White, G3SEK)
Date: Fri Feb 7 04:30:48 2003
Radio WC6W wrote:
>
>   That circuit is at least 40 years old... Why it has never been put 
>in the "handbook" and properly described is just one of those mysteries 
>of the universe...
>
Bruene, who invented the circuit, described it in QST in April 1959 but 
for some reason the description has never found  a permanent place in 
the handbooks. About a year ago I summarized Bruene's original article 
for my magazine column, and there's a PDF at:
www.ifwtech.co.uk/g3sek/inprac/best-of.htm#bruene

As Roger said, the toroid acts as a current transformer to sample the 
current, and the caps act as a voltage divider to sample the voltage. To 
set the bridge up correctly, those two samples must be equalized so that 
the 'reflected' reading is zero on a matched load. The trimmer cap 
adjusts the voltage divider to do that.

So there's your adjustment procedure - connect a good 50 ohm load, and 
adjust the cap for a null in the 'reflected' reading.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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