Spectral purity is even more important in amateur radio, as individual stations
do not have fixed frequency assignments ('channels') and no analysis of the
consequences of interference occurs prior to transmission. The practical
outcome of this is that some stations, especially those using a '12V DC'
transceiver set to full output power and then amplified, produce -60dBm
sidebands at my QTH.
Some of you may be content transmitting several watts of interference, but many
of us aren't and take whatever reasonable steps we can to prevent it.
73,
Mike - N8MSA
----- Original Message -----
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: amps@contesting.com
Sent: Friday, May 22, 2015 9:10:53 AM
Subject: Re: [Amps] SPE 2K RTTY Duty Cycle / spectral cleanliness
All good valid points that you make here Kevin.
There is also an equal fascination / obsession in some ham radio quarters
with IM3 and levels! We are talking here of HF amateur / ham band
transmitters NOT professional transmitters where spectral cleanliness is
more important.
It's the higher order IM stuff / crud that has to be curtailed...
The modern trend towards Adaptive pre-distortion techniques works well to
clean up mediocre PA transistors and sort of turn a sow's ear into a silk
purse.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Kevin Stover
Sent: Friday, 22 May 2015 10:28 PM
To: amps@contesting.com
Subject: Re: [Amps] SPE 2K RTTY Duty Cycle
There are NO 12V final amateur transceivers that make -40dB IM3, none. Never
have been, never will be. The best are at -33 to -35.
Those transceivers capable of 200 Watts are all usinng 28 or 50V finals and
can reach -40 depending on the low pass filter used behind the PA.It's time
for the manu's to get rid of this fascination with running everything off a
battery.
The most expensive part of any SS amp is NOT the finals themselves it's the
LPF that will take 1500 watts and keep harmonics legal (-43db HF, -60dB 6m).
That's not IM3. Name the amp that hits an IM3 of -40. The 8877 will come
close, the Russian triodes won't, none of the tetrodes will do it.
--
R. Kevin Stover
AC0H
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