On 10/30/2013 11:06 AM, Gene Fuller wrote:
A simple "line flattener", and some hardline, pretty near moves a
station located "tuner" to the antenna, giving probably as much or
more radiated power and a lot more convenience. Exceptions of course
for VHF and higher.
Gene / W2LU
Line Flattener? I'd not heard that term before.
73
Roger (K8RI)
----- Original Message ----- From: "Roger (K8RI) on TT"
<K8RI-on-TowerTalk@tm.net>
To: <towertalk@contesting.com>
Sent: Sunday, October 27, 2013 1:25 PM
Subject: Re: [TowerTalk] Fwd: Tower and antenna decisions
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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