Rick:
Nice installation. From the looks of your terrain, at least your shack
won't be torched during the next wildfire season. There is something to be
said for wide open fields, other than just antenna performance.
------------------ Wes Attaway (N5WA) ------------------
1138 Waters Edge Circle - Shreveport, LA 71106
318-797-4972 (office) - 318-393-3289 (cell)
Computer Consulting and Forensics
-------------- EnCase Certified Examiner ---------------
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Richard (Rick)
Karlquist
Sent: Saturday, May 23, 2009 11:52 AM
To: k2xx@swva.net
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Balanced Feedline for Ground Mounted Vertical?
Joe Giacobello wrote:
> If one had to install a ground mounted vertical as far as 2,000 feet
> from the shack and wanted to avoid the expense of using low loss coax,
> could a balanced feedline be used as an alternative? The idea would be
> to run the balanced feed line to the base of the antenna and connect to
> the antenna through a current balun. The input to the feedline and the
> antenna would be matched by means of a balanced tuner in the shack.
>
> Anyone have any thoughts on the effectiveness of this arrangement?
> Joe
> K2XX
Been there, done that, got the T shirt :-)
You can see photos of my 850 foot open wire line at:
http://www.n6rk.com/openwire.html
However, there is a giant disclaimer:
I only run my open wire line (OWL) in a matched condition. I do
not have the philosophy that having OWL gives me carte blanche
to attach a random wire to the end of OWL and tune it from the shack.
Maybe you can make this arrangement work after a fashion to
the extent that will satisfy your needs. Expect VERY narrow bandwidth
and fairly high losses in line if you proceed.
Now, what I have at each of the line is a 50 ohm current
balun in cascade with a 50 ohm balanced to 450 ohm balanced transformer.
The antenna tuner is located at ... the antenna (what a concept) and
remotely controlled. I do not have a tuner of any kind in the shack
(not even a pi-network output; my linear is solid state).
The loss of the (matched) line is easily predicted from graphs in
antenna handbooks. You need to decide how long, how much loss you
can tolerate, and what frequency. Assuming you use 450 ohms, that
will then determine the wire size and spacing. I don't know how
to make a good 600 ohm transformer, so I stick with 450 ohms.
It is certain to be WAY cheaper than coax. Unless someone gives
you 3000 feet of hardline for nothing, as happened to me. However,
by that time, I already had the OWL up, and it is somewhat
lower loss than the hardline. You can look at aluminum wire vs copper.
It's just a cost thing. Physics vs money.
I happen to have used 4 AWG insulated stranded aluminum. Evidently,
the insulation and stranding haven't hurt me in the loss department,
as the loss is close to the theoretical loss, which is in the tenths
of a dB on the low bands.
I have homebrew transformers. You can also buy various transformers.
I happen to think mine are better, but I am a perfectionist. I
wouldn't try to tell you the commercial ones won't work.
You will see on my web site that I support the line every 50 feet.
The supports have PVC pipe on the top with grooves cut by a router
at a spacing of about 5 inches, to get 450 ohms. The wires are
held in the grooves by gravity. If I want to drive the tractor
past the line, I just let down the line onto the ground by lifting
it out of the grooves. I found that it is not necessary to have
intermediate spacers to keep the line spacing perfect. When you get up
to 450 ohms, the dimensions are fairly non critical.
My vertical has relays (instead of traps) to adjust the length to
be a 1/4 wave on 40, 80, or 160 meters. Vis a vis the endless
discussion of the magic 43 foot vertical, once the vertical exceeds
5/8 wavelength, it starts to radiate upward. (43 feet is 5/8 wave
on 20 meters, duh). That is another reason why the tuner in the shack
idea is bad.
Rick N6RK
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