Steve,
You'll obtain better performance from dipoles or inverted vee's rather than
from a vertical on 40 and 20. Two dipoles or inverted vees attached to a
common feed will work well, especially if they're deployed at right angles to
each other. A better solution is two dipoles or inverted vees with separate
feedlines.
This solution will beat the pants off of a vertical on 40 and 20,
especially if you're not going to deploy an extensive ground system.
Good luck!
73
Frank
W3LPL
---- Original message ----
>Date: Tue, 3 Jul 2007 10:24:58 -0700 (PDT)
>From: steve d <kc8qvo@yahoo.com>
>Subject: [TowerTalk] Antenna feed methods?
>To: TOWERTALK@CONTESTING.COM
>
>
>I am going to be in Canada in a bit over a week and will be taking my radios
>along. Its mostly a VHF operation though - the grid is EN39, so if you are a
>grid hunter then look me up on QRZ.
>
>Anyway, I am going to use 40 and 20 for my contact frequencies. In past years
>I have used a screwdriver antenna for general HF fun, but its a compromise.
>Its pretty short and has lots of loading on the lower bands. So this year I
>would like to use a vertical. I am going to use about 48' of military tent
>poles as the pole.
>
>Now comes the question: What is the best way to feed this through a tuner to
>get multiband coverage?
>
>I set one like this up at field day (shorter, though) and worked everything I
>heard and loaded it up on all bands 160-15 (I dont think I tried anything
>higher). I fed it with ladder line to a T-tuner with an interna 4:1 balun.
>
>Since this is going to be used on multiple bands I dont want to use coax. The
>antenna is not going to present a 50z match to the line. If I get up to about
>3db of transmission line losses I will loose half my signal.
>
>Ballanced line doesnt have the same loss properties as coax when presented
>with a wide range of impedances, thats why I would like to use it. I also have
>a tuner that will work with it (palstar at1500cv).
>
>There are a few issues with running the line though - how do I get it inside
>the cabin?
>I could run it under the back door (along with all my other lines). This is
>the easiest method, but the door has a 4-6" wide metal plate on the floor with
>a rubber seal on it. The metal will interfere with the ballanced line. Unless
>that short of a distance wont matter much?
>I could do the same thing, only use two runs of coax through the door jam.
>I could also use coax to run from inside at the tuner to a balun outside, then
>ladder line from there.
>Or I could run two parallel lines of coax as ballanced line to the antenna.
>However, from what I have heard this doesnt make much sense - the loss through
>the coax would be the same as if it were run in one line.
>Another option would be to run some metal rods through the log walls, like the
>brass tubes you get at the hobby shop, and connect my ballanced line on to
>that. I dont know how possible this will be until I get there, though.
>
>What do you guys think? How can I minimize losses here?
>
>I know the best route would be a signle band antenna, but that would only get
>me on one band.
>
> Steve, KC8QVO
>
>
>---------------------------------
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