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Re: [TenTec] Omni V power limits

To: tentec@contesting.com
Subject: Re: [TenTec] Omni V power limits
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 01 Jul 2010 08:39:13 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Part of the reason for running low power with the digital modes is 
intermod distortion that causes increased bandwidth, and part is the 
available power dissipation of the radio. I have confidence the PA 
transistors in the Omni V have plenty of heat dissipation but the radio 
may not have quite enough. Thing to watch in RTTY (not so critical on 
intermod as PSK31) is the temperature rise of the heat sink. I'd look 
for a high volume muffin fan and fabricate mounts to blow air on the 
case heatsink. Optimally it would be controlled by a temperature sensor 
on near the PA transistors.

That being said, doubling your output power is less than an S-unit, when 
you need more power you probably need a 10 dB rise to overcome QRM and a 
sick receiver at the other end. 3 dB isn't going to ever make that much 
difference except in situations where the signal to noise ratio is less 
than 1 or 2 dB. Which isn't often and on HF the propagation losses on 
nearly any path vary much more than that from one second to the next.

As you increase the power output it would be good to have someone nearby 
but far enough away (or with an adequate receiver attenuator) that their 
receiver isn't being overloaded to look at the waterfall display to 
watch for extra intermod products on your signal.

73, Jerry, K0CQ

On 7/1/2010 5:12 AM, Bob Towers wrote:
> I run a lot of digital modes and normally keep the power below 50 watts.
> Just occasionally - ie in contests - I need a little more power,
> especially using RTTY.
> What's the maximum power I could run using RTTY and, say MFSK, which - I
> think - is a 100% duty mode?
> 73
> Bob
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