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Topband: Collins 312B-4 wattmeter OK on 160?

To: topband <topband@contesting.com>
Subject: Topband: Collins 312B-4 wattmeter OK on 160?
From: Mike Waters <mikewate@gmail.com>
Date: Sat, 4 May 2013 22:31:18 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
The Collins 312B-4 speaker console with wattmeter (the only wattmeter I
own) is rated 2 to 30 MHz. Has anyone found any issues with it at the legal
limit on 160m?

Into a low SWR (like my 50 ohm Heath Cantenna) at 100 watts, the Collins
wattmeter seems to read fine on 160. But there's something odd about a lot
of high-power readings I've seen on 160 compared to the other bands.

For one thing, the Collins meter disagrees with the built-in SWR meter on
my Icom IC-765 on 160, unless the SWR is very low. (On the other bands,
they pretty much agree).

Another thing, as the reflected power increases, the forward power does not
move up much on 160 like it does on the other bands. It's like it's stuck
around the 1500 watt level, as if the toroidal ferrite core in the Collins
directional coupler is saturating on 160.

And if that is true, that would explain another issue: why increasing the
plate voltage to 4 kV --or more-- hardly raises the power level much above
1400 watts no matter what I do to the pi-network, which uses a rotary
inductor.

Maybe it's an amplifier issue. I have an odd amplifier on 160. (
http://www.w0btu.com/833C_linear_amplifier.html :-)

73, Mike
www.w0btu.com
All good topband ops know fine whiskey is a daylight beverage.
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