Transmitter is always adjusted for max or rated output thus RF Level is
always 100%. The level from the sound card along with the respective input
control on the radio is then adjusted to produce 30 to 35 watts of output
with PSK-31 data. For RTTY I use AFSK mode and adjust the soundcard or
respective input control on the radio for 50 watts output. No additional
cooling is used under these conditions. Speech processing is always OFF and
the levels are such that the ALC LED does not illuminate.
Typical ALC action or Speech Processing action produces non-linearity in the
PSK data and most likely sidebands are generated that consume excessive
bandwidth. A clean PSK-31 signal actually occupies ~31 Hz of spectrum. Add
some IMD or distortion and that bandwidth can easily be 3x or 4x or 5x the
normal amount. With this occurring, the effective communication power is now
spread across the sidebands and are basically of no value on the receive
end. Hence the transmitter power is now spread across the wider bandwidth
and the result is the effective communication data power is reduced in terms
of bandwidth power. This is one reason that small amounts of PSK power
values are very effective means of communications. Modes that use wider
bandwidths require more power to attain the same level of effective
communications.
73
Bob, K4TAX
----- Original Message -----
From: "Larry Rockne" <wa7hdz@clearwire.net>
To: <tentec@contesting.com>
Sent: Tuesday, March 18, 2008 4:06 PM
Subject: Re: [TenTec] OmniV and PSK31
Bob, K4TAX, et all
I'm one of those 'Hams' that make PSK too difficult.
I set my 'rf out' @ 30% and went along fat, dumb, and happy working
stations even tho my ALC led was on.
Thanks for the info.
73's & CUL Larry WA7HDZ
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