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Author Topic: 6 mtrs and 102" whip  (Read 494 times)
AE7GL
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Posts: 62




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« on: December 07, 2004, 09:41:13 AM »

Am I correct that a 102" whip with the spring(108" total) is almost the exact length needed for a 1/2 wave antenna for 6 meters? Possibly a little long if you count the ball mount as well, but by shorten the whip a couple inches it should be right on.

Also, how usable would this setup be for 10 meters without adding an auto-tuner.

Thanks,
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AA4PB
Member

Posts: 12697




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« Reply #1 on: December 07, 2004, 10:47:10 AM »

L(ft)=468/f(Mhz)

108-inches is 1/2 wavelength at 52 Mhz (6M). You can't directly end feed a 1/2 wavelength antenna with coax because the feed impedance is very high (2000 ohms perhaps). You'll have to have an impedance matching network of some type (tapped coil).

108-inches is 1/4 wavelength at 26 Mhz. Again you'll need some type of tuner or matching section to make it work at 28 Mhz (10M). Or, you could shorten the whip to make a total of 100-inches which is a 1/4 wavelength at 28 Mhz.

If your idea is to use the 108-inch whip on both 6M and 10M without making any other changes, it won't work. You'll need a tuner designed for end fed whips or the easier solution is probably just to have two different length whips, one being 1/4 wavelength on 6M and one being 1/4 wavelength on 10M.
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WB2WIK
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Posts: 20547




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« Reply #2 on: December 08, 2004, 11:19:38 AM »

I get the feeling you may not know that you really cannot use a "1/2-wave whip" antenna without doing a lot of work to match it.  Feeding a 1/2-wavelength whip with coax and without a matching network between the coax and the whip isn't going to cut it, you'll never transfer any power to the whip.

The 102" whip is 1/4-wave for CB, and works fine.  That's the reason most whips actually are 1/4-wavelength long: It's a length that provides a good match to coaxial cable.  1/2-wave doesn't.

WB2WIK/6
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AE7GL
Member

Posts: 62




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« Reply #3 on: December 10, 2004, 08:58:59 PM »

No, I guess I didn't know you couldn't end-feed a half wave antenna. Or I've forgotten. At any rate. Thanks for the info. Both to AA4PB and WB2WIK. That's why I ask here when I haven't found an answer on my one. You usually get lots of good help from lots of good people. I guess I'll probably trim it to 1/4 wave for 6 meters and then add a tuner when I add the HF.

Thanks again,
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KA5S
Member

Posts: 229




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« Reply #4 on: December 12, 2004, 08:11:10 AM »

You can tune an end-fed half-wave antenna with an L-network *at the feedpoint*. You might even be able to leave it in-line on ten and just detune it. However, the voltage at the feedpoint even at 100 watts may be more than the usual ball-mount can stand.

Cortland
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