In a message dated 8/20/01 1:32:47 PM Pacific Daylight Time,
mpride@us.ibm.com writes:
<<
Why not keep the ladder line all the way into the shack and put a tuner on
it to conveniently cover the bands of interest. To run the open wire into
the shack (like go through walls or windows, etc.), use some equal length,
short runs of coax, and connect two coax lines in parallel, center
conductors connected to the openwire, then direct into the tuner - ground
the braids together of the two parallel lines.
Stay away from the baluns - creates loss.
OR, Consider a simple 3 element tribander pointed south (30 or 40 ft. high)
and an inverted vee for 40 M on that tower - either a relay on the tower to
one feedline (coax) or two feed lines. Don't think you will benefit much
with a wire on 10 or 15 and still be competitive to the south.
Regards,
Mark, K1RX
GALE STEWARD <k3nd@yahoo.com>@contesting.com on 08/20/2001 03:33:11 PM
Sent by: owner-towertalk@contesting.com
To: towertalk reflector <towertalk@contesting.com>
cc:
Subject: [TowerTalk] Ladder Line and Coax
Have been thinking of installing a simple antenna to
cover the SE in contests and as a backup in general.
Was considering a inverted vee hung from the tower and
fed with ladder line & tuner. I want to cover only 10
thru 40. My question is this: my tower is about 100
ft ftom the house and want to feed this antenna with
ladder line near the ground, how do I handle that
transition to coax? A 4:1 balun, a 9:1 balun, other?
Is it even worth doing with the losses incurred due to
the mismatch in 100 ft of coax? Maybe a trap dipole
or inverted vee would be more appropriate? I just
wondered if anyone had tried something similiar and
how it all worked out.
73, Stew K3ND
>>
Running balanced coax through the walls has the problem that a high voltage
area may be in that area on some or all bands. The way you control and or
know what the Z at the end of the feedline is to have a length that is a 1/2
wave or multiple on all bands with the open wire length of 137' or 123' of
450 ohm ladder line. If you know what it is at the antenna it's the same at
the end of the feedline.
You may have a Lo-Z at the end of a 450 or 600 ohm feedline and a 9:1 balun
wants to see 450 ohms. Random lengths of open wire line that ARRL always
suggests-- creates problems and Z's that some tuners may have arcing problems
won't match.
With the feedline I suggest and a trapped dipole you will have a Lo-Z at the
end of the feedline for the tuner to match. Link coupled finals would match
it directly. I've run open wire line right through walls and floors without
a problem. To go through walls and floors I've used various 3/8" hollow
insulators for the open wire line to the tuner. It works just fine with the
least losses and minimum values of reactance on the various bands.
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