Even if you have a clean, low distortion signal, while using an amplifier,
you need to keep the output to 50W or so to avoid causing AGC compression in
the receivers of the other stations in the PSK-31 sub-band. Don't forget
that in PSK-31, many stations are simultaneously using a single 2500 Hz SSB
bandwidth with a recommended output of 30W. When there are QRO signals in
the waterfall, the receiver AGC typically causes the weaker signals to be
less likely to be decoded as their audio will be reduced..... its fairly
easy to figure out which signal in the waterfall is causing the other
signals to be compressed but its difficult to politely convey to the
perpetrator the damage being caused. Few DX-peditions want to offer PSK-31
contacts for the very reason that many operators will not abide by the
self-imposed low power necessary to share a PSK-31 sub-band.
From: "Richards" <firstname.lastname@example.org>
Sent: Thursday, July 01, 2010 3:08 PM
To: <email@example.com>; "Discussion of Ten-Tec Equipment"
Subject: Re: [TenTec] Omni V power limits
> Does this sort of distortion occur if I run the rig at a moderately
> low power output, and let a linear amp make up the difference?
> In other words, if I keep the rig running real easy and clean, will
> the amp, itself, add an undue amount of distortion? I thought
> that would allow the amp to run kinda easy also.
> Interesting thread.
> =============================== K8JHR ====================
> On 7/1/2010 9:39 AM, Dr. Gerald N. Johnson wrote:
>> 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.
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