----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "AA6DX - Mark" <aa6dx@cox.net>; <richard@karlquist.com>; "Jim Lux"
<jimlux@earthlink.net>
Cc: "TowerTalk" <towertalk@contesting.com>
Sent: Monday, May 16, 2005 7:07 PM
Subject: Re: [TowerTalk] Mini Lini on the Tower?
> > In any event, getting the most (however you want to define
> "most") out of
> > an array driven with multiple amplifiers is a somewhat
> tricky
> > proposition. If nothing else, having separate amplifiers
> that you want to
> > run at full tilt leads to some optimizations for patterns
> that run counter
> > to traditional approaches which tend to try to maximize
> overall RF
> > efficiency (that is, power radiated in the desired
> direction over RF power
> > put into the system).
>
> Before I got involved deeply with a complex system I'd like
> to see IMD tests on a single brick.
> There's a great deal that can go wrong with linearity in a
> class E system used as a linear amplifier.
I'd generalize that to any amplifier, not just Class E.
Most amplifiers sold in the amateur market have precious little "real"
performance data. Not surprising, given that they are sold inexpensively.
At least for "traditional" designs, even if you don't have real test data,
you DO have decades of experience of others to draw from. After all, people
have been building HF triode amplifiers for nearly a century, and the
designs used today aren't all that different than those used in 1930.
Naturally, we're all guessing from the very sketchy words on SGC's web
pages, but, if they are doing Kahn EER, that method has been studied, and
built, for 40 or 50 years. As far as Class E goes, that's been around a
while too. With all these more sophisticated designs, a lot depends on the
details, though.
>
> Can you imagine anyone who went through the trouble of
> putting up several antennas for one band (in a stack)
> wanting to give up several dB of power when using one
> antenna? I sure can't!
>
> Then there's the receiving issue.....and lightning.....and
> you still have all the same common mode RF in the shack
> issues but now you involve low power leads carrying high
> common mode currents (if antenna design is flawed).....
I would imagine that one would use something like shielded twisted pair (or
twinax, or,...) to carry the RF up to the amp, and use a transformer.
Sending low level signals in a high RF environment isn't exactly rocket
science. It's not familiar in the typical ham environment, but how to go
about doing it is fairly well known. And, the first few folks doing it are
going to spend a bunch o'bux because they'll make false starts, etc. and
there won't be established low cost amateur suppliers.
Mind you, if I were doing it, I'd be using optical fiber for the
interconnects, not coax. Cheaper than low loss coax, and zero EMI problems.
For that matter, I'd be giving serious consideration to putting the radio at
the antenna, and just sending the baseband information back to the shack.
Yep, there are some thermal design issues to resolve (most ham radios won't
tolerate outdoor temperature ranges), but there'd never be all those
discussions about what kind of lightning arrestor/surge suppressor to
install where the cable comes into the shack.
There's no real good reason these days why the front panel of the radio has
to be in the same place that the RF electronics is.
>
> So...what's the advantage again? Light weight for portable.
The advantage is that it's a new technology, which, in the long run, has
great potential. Such innovation should be encouraged because it "advances
the state of the radio art", which is one of the reasons we amateurs get to
use valuable spectrum for free. The SGC implementation may have problems,
but it might also have unique advantages, both of which nobody will know
until people start to actually use them.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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