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Re: [TenTec] 160 M antenna

To: tentec@contesting.com
Subject: Re: [TenTec] 160 M antenna
From: Jim Brown <k9yc@audiosystemsgroup.com>
Reply-to: k9yc@arrl.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 06 Nov 2013 16:00:31 -0800
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On 11/6/2013 3:34 PM, resluder@yahoo.com wrote:
What kind of bandwidth do you get with your inverted L, 50 kHz?  Would I still 
be able to use a tuner in the shack if I want to bend it for more coverage on 
160?

Define bandwidth. Do you mean SWR bandwidth? Do you mean you can get it to load?

If you can get the total wire length > 100 ft and connect it to a decent radial system, a decent tuner should be able load it across all of 160M, but you'll need to retune it as you QSY. The Ten Tec 229 and 238 series tuners work very well on 160M with reasonably good antennas.

I have a Tee vertical for 160M that's 86 ft vertical with roughly 100 ft on top. That makes it longer than a quarter wave, and I've adjusted the length of the top section so that the feedpoint Z is 50 ohms resistive plus some inductance (because it's electrically long). I then added series C to tune out the L, giving me a nice match to 50 ohms. I can work at least the bottom 75 kHz of 160M without much tuning.

A well known way of broadbanding almost any antenna is to make the conductor fatter. An easy way to do that is to use two spaced conductors, tied together at both ends, and that's what I did. The vertical is two #10 THHN wires spaced about 6 inches. I did that, and the SWR bandwidth improved by at least 50%.

As to loading a 45 ft wire on 160M, which Jim asked about. I'd guess that the Ten tuners will LOAD it, but the radiation resistance of such a short wire is pretty low, so it won't be very efficient without a great radial system. Remember that a vertical is a simple series circuit -- radiation resistance (Rr), wire resistance (Rw), and ground resistance (Rg). The radiation resistance is the "good" resistance -- it accounts for radiated power, but the same current flows in all three resistors, so the power divides between them. For the antenna to WORK, we want Rr to be much larger than (Rw + Rg), but it takes a lot of wire to get Rg below 10 ohms on 160M, and Rr of a 45 ft vertical won't be much more than perhaps 6 ohms, yielding an efficiency of about 30%. That means your 100W radio will put 70W into the ground and 30 watts into space. .

73, Jim K9YC
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