Paul, your antenna is the best practice of how to build it.
One single wire (per side) from matchbox to end insulator.
Too often we get hung up here on "best practice (but impractical)" vs.
"practical but less efficient" designs.
If something is impractical or too expensive, then the next best thing is to
find the best compromise and run with that.
Each time I try to show what that is, I get jumped on by engineers quoting text
books which we all have read a dozen times.
It is as you say, the low Z is in your case rare, but on this side of the pond
it is almost the norm.
Most people build these antennas using 2x 5m, 2x 6m, 2x10m, or 2x 13m.
Our back yards are too small for longer antennas.
THAT is when you need the C on the other side.
I am focusing on showing people how to make the best of what they have and get
on the low bands and still have moderate success and loads of fun. Engineers
preaching that everything must be perfect to be any good are a big burden on
our hobby. It's a hobby and should be fun.
Cheers Paul!
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Paul
Christensen
Sent: Monday, July 18, 2016 1:47 PM
To: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] OT: Question to the group
Rick,
Nice discussion on your website. I'm presently using a symmetrical switch-L
tuner at my home QTH. It's mounted outside the shack in a pressurized NEMA
enclosure. A 1:1 choke is placed on the input. A pair of vacuum relays
switches a motorized vacuum relay either side of a pair of ganged, motorized
tape inductors. In retrospect, I would not have used the C switching
arrangement to cover both Hi-Z and Low-Z line terminations. Doing the math,
there's almost never a resulting line input Z of less than 50-ohms when using
full size antennas at least a half-wave in length -- no matter the line length.
If the resulting line input Z is less than about 30 ohms, it's an antenna I
don’t want in the first place. The only exception being a mobile antenna. So,
done again, that arrangement would be eliminated saving on cost, complexity,
and loss.
The tuner works well but not as efficiently as a link-coupled tuner. However,
out of convenience and due to home RFI considerations, I decided to use this
design. With so many home appliances using switching supplies and noisy
microprocessors, it's difficult to use balanced feeders through a house or
apartment today. Line balance is one thing, but these lines cannot completely
cancel RFI coupled on receive from various directions. Transposition blocks
may help as used in the olden days.
A remote-controlled link tuner would by my Holy Grail, but the mechanical
complexities start getting in the way of improved efficiency. To do it right
would require separate link coils moved on a rotating turret.
I would much rather deal with slightly higher tuner loss (under some matching
conditions) when compared to resonant antenna coaxial line loss. The primary
benefit being all-band operation and a very simple antenna feed. Here, a
600-ohm feeder never breaks its connection: the transmission line wire simply
turns at the feed point to form the antenna. It truly is a zero maintenance
antenna -- the only maintenance needed if the wire actually breaks. With this
feed, one never has to worry about moisture ingress, UV destruction, etc.
Paul, W9AC
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