On 10/27/2013 10:10 AM, Jim Lux wrote:
On 10/26/13 8:15 PM, Hans Hammarquist wrote:
All these "modern", solid state, PA have the same problem, they are
"protected" and the "protection" rolls back the power as soon as they
detect reflected power. Little depending on make and design they roll
back more or less. That's why the manufacturer offer built in tuners.
The "old days" with a pi-filter on the output could be tuned to most
anything below SWR of 1:3 or even more, and they didn't have (needed
maybe) the "protection". As long as you didn't kill the final tubes
by overheating them, you were OK. Do we like to have the "old" tube
final back? Maybe.
I would rather have "smart antennas" with the finals *at the antenna*
and the matching done there.
This gets back to what I want to do...sorta.
Particularly on 160 you don't have a lot of room to make frequency
excursions and that is to put the tuner "at the antenna", but that comes
with a location that is hazardous to the tuner's health. Another is just
how good are the remote autotuners? Will they take the SWR right down
to 1:1 which is important for SS amps, not because of power, but because
of deteriorating signal quality.
With a remote tuner, I want to match the antenna impedance, not just
move the resonant point. Yes, if I move the resonant point to cover the
entire band it does make life easier and I could take care of the rest
in the shack, but again I'd prefer to do this at the antenna so in most
cases I only need a small L network even for 160 if it's close to resonance.
With the half sloper other than the difficult maintenance problem this
becomes rather easy although on 160 that makes for a lot of resonant points.
putting the matching network at the antenna for a center fed, half wave,
sloping dipole is not practical although a single band tuner at the
tower using open wire line might. Ice storms are common here spring and
fall, although there are far fewer in the fall but the make open wire
problematic and to me, reliability/durability is important because I
have to impose on others to get things fixed.
Sure, it's more complex than the historic Transmitter in
Shack/Feedline/Fixed Antenna, but life moves on.
For instance, I sketched out an interesting design for a form of Yagi
with all driven elements, using an array of magnetic loops, rather
than the traditional horizontal elements. The matching from low Z
semiconductors to the low Z of the magnetic loop is actually kind of
what you want. And you're doing spatial combining, so with 5
elements, each driven with a 200W module, you don't have the losses in
the power combiner you see in a "single output" SSPA.
Combine this with things like polar modulation, and you can get some
very interesting designs. It's almost like having the entire rig at
the top of the tower, and all you need is power and an ethernet link,
which could be wireless.
Sure, its nothing like ham radio in the past, but that's what ham
radio is all about: try new things.
I like the idea and to me it's far less different than a remote regular
station, controlled over the internet. You're just combining the rig
with the antenna. There might be issues with lightening, maintenance,
and cost though. Could it be made to match the big mono band Yagi for
performance?
It's a radical design, but used much the same way as ham rigs have since
day one.
73
Roger (K8RI)
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