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From: wjc%ll-vlsi@tgr.UUCP
Newsgroups: net.ham-radio
Subject: Re: high power abuses during contests
Message-ID: <1865@brl-tgr.ARPA>
Date: Thu, 23-Jan-86 12:56:46 EST
Article-I.D.: brl-tgr.1865
Posted: Thu Jan 23 12:56:46 1986
Date-Received: Sun, 26-Jan-86 20:23:56 EST
Sender: news@brl-tgr.ARPA
Lines: 29


It's not just during contests.  I mainly operate on 6 meters, and there are some
noteable examples of wide amplifiers.  Part of the problem is probably due to
improper operation.  However, a great part is due to non-linear amplifiers!

If you look at the specs for something like a Mirage 100-watt solid-state amp,
you will see that they claim something like 40 watts out for 2 watts in and
100 watts out for 10 watts in.  Clearly, this is not linear and leads to some
distortion.  Also, many of the tubes used in amateur high-power amplifiers
leave something to be desired in terms of linearity.  For example, Eimac claims
that a 4CX250R running 295 watts PEP plate power output will have a 3rd-order
IMD suppression of only 25 dB.  Thus, you would be outputting almost 2 watts
of 3-rd order distortion.  A 3-400Z has 28 dB of 3rd-order suppression and a
3-1000Z has 29 dB.  I believe the 4CX1000 series falls in this range, too.

For better linearity, you can use tubes like the 4-400 (35 dB), 8873 (35 dB),
3CX800A7 (36 dB), 8877 (38 dB), 3-500Z (40 dB), 4CX1500B (43 dB), and the
8938 (44 dB).  It probably doesn't make sense to use tubes with better
linearity than these unless we start using cleaner exciters.  A quick exam-
ination of equipment reviews in QST shows that most modern rigs have about
32 to 36 dB of 3rd-order IMD suppression.  Also, "ultra-linear" tubes are quite
expensive.

All of the above is on my mind because I'm starting to plan a 6-meter amplifier
that will run within 2 dB of the legal limit, and I want it to be clean.
Anyway, I will post any interesting findings.

Bill
N1CPK