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Re: [CQ-Contest] Tuning Sensitivity Of Modern Amps

To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Tuning Sensitivity Of Modern Amps
From: K3BU@aol.com
Date: Sat, 5 Feb 2005 11:54:03 EST
List-post: <mailto:cq-contest@contesting.com>
In a message dated 2/5/2005 11:14:03 AM Eastern Standard Time, 
k8cc@comcast.net writes:
>>These high gain designs are wonderful when you tune up on 
a frequency and the load never changes (like in a broadcast or commercial 
application) but for us hams (and particularly contesters) the load 
sensitivity is a pain.

One remedy is to try to have antennas around the 50 ohms and as broadband as 
possible. I always try to use quarter wave Bazooka baluns on monobanders (good 
band filter too), its reactance is opposite of antenna's reactance change 
with frequency, so antenna SWR appears flatter.

Another solution is to have (homebrewed amps) separate tuned or PI output 
circuits, optimized for each antenna and relay switched with antennas.

This is also where amps having some power room to spare can be tuned as K3LRs 
tip and can be more forgiving for those extreme situations.

The last resort is pretune the amp for various antennas and frequency 
extremes and use old magic marker label trick. When parking on new frequency 
prolonged stay, just set the controls to required spots.

Solid state amps most likely will cut the power back when presented with 
higher SWR.

Yuri, K3BU.us
160m records updated at http://members.aol.com/k3bu/160Records.htm
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