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
----- 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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