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Old 03-06-2019, 07:14 AM
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Default DIY Half-Wave Dipole for VHF (not a Yagi)



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A while back, I built a half-wave dipole out of a tape measure that has a 1.4 SWR that's pretty flat across the 2m band. I wanted something better for my handheld that's better than the Nagoya NA-771, and can be mounted to a pack or plate carrier while the radio is in a pouch. Have some slight tweaks if I build another one, but I'm pretty happy with how it turned out.

Pics and instructions here:
http://www.tothewoods.net/Comms-how-...dipole-vhf.php



I built another with a wire for the ground element, but it has a high SWR. I think I have the fix, though...MTF when I get a chance to build another one of those.
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Old 03-07-2019, 07:16 AM
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That's a very clever idea. Very well done webpage too. I'm gonna note this for future reference.
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Old 03-07-2019, 11:12 AM
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I like it. It looks very solid. Well done. It will transceive.
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Old 03-28-2019, 04:16 PM
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Added a new pic of it mounted on a backpack with the Code Red hand mic on the shoulder. With this setup, the radio goes in an EMDOM GPS pouch that folds down to access the radio without taking it out.
https://www.emdomusa.com/Emdom-MM-GP...h-p/eu140a.htm

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Old 03-28-2019, 10:47 PM
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Very clever idea. Built the tape measure yagi a few years back and it performed surprisingly well.

Will have to try it sometime and see how it compares to my roll up j-pole.
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Old 04-01-2019, 01:03 PM
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Very cool Jeff! This is exactly what I've been wanting. I bookmarked this page and the linked page so I can build one in the summer.

FYI, in case anybody doesn't know, the Motorola HT1000 UHF or VHF has the same antenna connector as the Baofengs, which is nice.

.
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Old 04-01-2019, 01:11 PM
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Glad you found it useful! I was working on a similar antenna that screws onto the radio instead of having a separate cable but I couldn't get the SWR where I wanted it yet. Still pondering....
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Old 04-22-2019, 06:33 PM
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On VHF the polarization of the signal becomes important. Ideally, if you use your dipole horizontally it will have a 20db reduction on vertical polarized signals.
AG4YW
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Old 04-22-2019, 07:30 PM
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That's good to know. Can you point me to the math that calculates 20db?
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Old 04-22-2019, 09:52 PM
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Quote:
Originally Posted by Kerryphillips View Post
On VHF the polarization of the signal becomes important. Ideally, if you use your dipole horizontally it will have a 20db reduction on vertical polarized signals.
AG4YW
You can use that to your advantage when talking fixed point to point with another camp, by putting both antennas in a horizontal position with long sides parallel to each other you can reduce interference or jamming by others and make your signals less likely to be heard by others. Just remember to go vertical when communicating with others on the move.
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Old 04-22-2019, 09:59 PM
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Quote:
Originally Posted by Just Jeff View Post
That's good to know. Can you point me to the math that calculates 20db?
The 20 dB is pretty much a "rule of thumb" it can be influenced by the mounting arrangement and the way the feed-line is positioned.

I had a customer once, in a way far suburb of Chicago that had a RF control station, a 100 foot tower and Yagi antenna to talk to a tall repeater in downtown Chicago. But it didn't work very well. As soon as I arrived and looked at the antenna installation I knew exactly what was wrong. He had a TV antenna installer put up the tower and Yagi. Nice tower by the way.

The Yagi was mounted horizontally and most of the signal was not received at the repeater and vice versa. The installer thought it was for a TV and mounted it the way TV antennas are mounted.

There is less man made noise pick up in horizontal plane, so TV's are horizontal, but mobile radios use vertical whips so the repeaters and control stations must be vertical to match.
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