Figure out what the impedance of your 80m dipole is going to be at 160m (no
need to be gnats eyelash accurate).. any of the simple modeling programs
will work. Make sure you calculate for the frequency range, so you have the
whole range of impedances you're likely to match. (If you don't have a
modeling program, maybe someone on the list will run a quick and dirty
model...)
Download a copy of XLZIZL from AC6LA's website.
http://www.qsl.net/ac6la/xlzizl.html
Plug in your calculated impdedances at the frequencies of interest
Plug in your open wire transmission line length
Start fooling around...
You can put in matching transformers, etc. and see what happens.
The antenna's going to be pretty severely capacitive, and your feedline
isn't all that long, so it will probably look capacitive at your shack end,
so maybe a big low loss appropriately tapped loading coil might be a good
solution... provide both the inductive reactance you need and some impedance
transformation to close to 50 ohms. The tuner can take care of the rest.
The spreadsheet can do these calculations too.
----- Original Message -----
From: "Steve" <steveac@charter.net>
To: <towertalk@contesting.com>
Sent: Sunday, January 16, 2005 9:53 AM
Subject: [TowerTalk] 80 meter dipole on 160
> I have 80 and 40 meter dipoles on a common center insulator. They are
> fed with about 60 ft of open wire transmission line whose characteristic
> impedance is about 500 ohms. I'd like to use this antenna on 160 meters
> and am looking to do so with an antenna tuner that has only 50 ohm
> unbalanced output.
>
> What's a good balun to use at the rear of the tuner to convert from the
> unbalanced tuner output to the open wire line? Buy or build? I need to
> accommodate legal-limit power.
>
> Is there any point in trying to do some impedance matching with the balun?
>
> Thanks.
>
> Steve K8JQ
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|