Jim, I think some of these small footprint SS amps are just so compelling
and attractive to hams, particularly the DX Expeditioners who lug them to
remote locations, prospective purchasers rely more on fellow ham word of
mouth and their own assessment of how they sound on-air; rather than being
overly influenced by manufacturer's marketing specs.
The IMD of the Yaesu Quadra, the Icom PW-1, and the more compact THP, SPE
Expert, etc, at their respective rated power output is nothing to write home
about and is mediocre at best. However, the average ham deems them to be
"good enough" to meet my below aforementioned criterion. Technocrat purists
live in a sheltered world all of their own. Few hams run the likes of a
Harris RF-110A amp or modern SS equivalent.
When homebrewing big SS amps I've found designing 'em big and de-rating them
a couple of dB below sat Po yields plenty adequate IMD performance for clean
ham band SSB use. Certainly commensurate with the IMD of modern transceiver
PA stages and their associated ALC Tx power control loops.
Inefficiency is the inevitable trade-off one makes when wanting to run the
SS amp clean.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Thomson
Sent: Tuesday, 5 March 2013 11:56 PM
To: amps@contesting.com
Subject: [Amps] Expert 2K / lack of specs
Date: Tue, 5 Mar 2013 09:34:17 +1030
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: <amps@contesting.com>
Subject: Re: [Amps] Expert 2K / lack of specs
Gentlemen,
I would not worry too much about the lack of specs; they would be quite
predictable and probable mediocre in respect of IMD performance.
All that really counts is that users of the Expert 1K or 2K amp do not cause
a nuisance to other adjacent users of the band in terms of IM crud and
buckshot and the SSB signal is not too wide in frequency occupancy; if any
amp meets that key criteria, then it is good enough for ham use.
The ones that I've heard on air meet this criterion.
Leigh
VK5KLT
## say what? When you spend between $5K-$10K on an amp, it damn
well better come with specs well beforehand, lotsa of em, and it had better
meet those specs.
## You are probably correct. IMD is probably lousy like -24 to -30 db pep,
typ ham junk. You could drop the drive down a bit...and clean up the imd,
but then it runs inefficient. Hence the lower power levels on some of the
SS amps, like 500-1000-1500w merely lower the voltage a bit, so the Z's stay
the same, and eff stays the same. Problem is the imd does not improve.
## what they need to do is design a real low imd 1.5 kw amp...such that
Z's come out correct for the combiners used etc.
## Plan B is just buy a commercial grade marine amp. Then you get the
real deal. Then it will have low imd, and meet fcc/itu specs.
Jim VE7RF
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