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Re: [TenTec] openwire feed OT

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] openwire feed OT
From: John Nason / NA9U <na9u@arrl.net>
Reply-to: na9u@arrl.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 31 Jan 2006 10:09:41 -0800 (PST)
List-post: <mailto:tentec@contesting.com>
Hooking the coax to the open wire feeder presents a
significant impeadance mismatch.  Most open wire is
300 to 600 ohms and coax is 50 to 75 ohms.  This would
negatively impact power transfer.  Since your going
from one transmission line to another this is
problematic.    

The impeadance of a dipole in free space is about 72
ohms at the center feed point which is why you can
feed it directly with coax.  Of course site conditions
usually drop the dipoles impeadance quite a bit.

You can also feed the dipole with the higher
impeadance open wire feeder and be ok because you are
transfering power from a high impeadance source to a
low impeadance load.  The key point here is that the
antenna is the load, not another transmission line.   


I have found over time that you can do almost anything
with anything.  The problem is how optimal is the
setup.    

John

--- Paul DeWitte K9OT <k9ot@mhtc.net> wrote:

> I would like to reopen the discussion on getting
> open wire into the shack.
> A while back there was quite a discussion on
> wheather to use a 4-1 or a 1-1
> balun when going to coax from open wire outside the
> shack and then running
> coax in to a tuner.
> 
> No one mentioned just hooking the coax direct to the
> open wire without a
> balun.
> 
> First I realize that you are going from balanced to
> unbalanced. How would
> this differ from feeding a dipole direct with coax
> and not using a balun at
> the feed point?
> 
> I would like to put up a temporary loop and it is
> not feasable to run
> openwire in to the shack. But I would like to feed
> it with open wire from
> the loop to where it comes into the house (cheaper
> than buying more coax).
> So I am looking for suggestions.
> 
> Since I am all T T it is only partly off topic.
> 
> Thanks
> 
> 73 Paul K9OT
> 
> 
> 
> 
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