More important than power is a clean signal when using PSK-31. A QRP but
clean (low IMD) signal is easier to copy than a stronger but dirtier (high
IMD) one. During contests, those running higher power with high IMD are
obvious.... some just avoid the QRO stations hoping they give up and go away
73,
Gary - AB9M
--------------------------------------------------
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Sent: Thursday, July 01, 2010 8:39 AM
To: <tentec@contesting.com>
Subject: Re: [TenTec] Omni V power limits
> 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
>> MM0RKT
>>
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