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KC2UGV
09-29-2010, 03:24 PM
A 1/4 wave vertical dipole doesn't work so hot for 2 meters. I could never get the thing tuned to the ham band (It "liked" 129 MHz or so best), and had a really wonky impedance that I could never get match.

I found a 1/4 dipole design somewhere, and the web page said,"It works great!". That might be accurate, but not with my system until I get the coax replaced with something other than 75 Ohm cable.

So, back to my "tried and true" antenna for 2 meters: The 1/4 wave droopy ground plane. I'm taking my time building this one, because I killed a length of coax by not sealing with well enough, and it leached water down the entire length. One good thing? This spool of cable cost me about $10 for 1000 ft.

So, this ground plane will be "well engineered" and not "ad hoc" as has been my past designs. I think for now, I can't beat the 1/4 ground plane. A beam is the next "step up", but I have to have an omni design. Have to complete this by week's end so I can try to get a new HF antenna designed, built, and up before the first snow.
W5RB
09-29-2010, 03:36 PM
You need to bring your feedline away from a dipole at about a 90 degree angle , for a half wavelength or more , or it'll be hinky . That's sometimes impractical with a vertical dipole . The droopy ground plane , as built using a chassis mount so-239 and brazing rod , works well on 2m , and fair on 440 as well .
N2CHX
09-29-2010, 03:40 PM
A matching stub might be necessary as well. FM stations use variations of dipoles and impedance matching is accomplished with a shorting stub. Pretty easy to make.
NQ6U
09-29-2010, 03:44 PM
I'm a firm believer in J-poles for VHF. Not only are they easily tunable, they're generally 5/8 wave which has a lower radiation angle.
PA5COR
09-29-2010, 03:57 PM
Diamond X510N.
Use car wax put, on roof with Ecoflex 15 coax, done for 2/70 9dB and 11 dB gain.

;)
KC2UGV
09-29-2010, 05:36 PM
You need to bring your feedline away from a dipole at about a 90 degree angle , for a half wavelength or more , or it'll be hinky . That's sometimes impractical with a vertical dipole . The droopy ground plane , as built using a chassis mount so-239 and brazing rod , works well on 2m , and fair on 440 as well .

I think this might be the issue here. I just brought the coax down the support, right next to the "ground leg" of dipole, and when you reminded me of the 90 degree thing, I realized there's coupling involved, essentially giving me no ground leg...

Well, I think I'll try it again, this time following the 90 degree rule. And, the J-pole is the next project :)
KC2UGV
10-02-2010, 08:51 PM
I'm a firm believer in J-poles for VHF. Not only are they easily tunable, they're generally 5/8 wave which has a lower radiation angle.

I was just re-reading this thread... I thought 5/8 waves had a higher angle than 1/4 waves?

Not really "questioning" you per se... I guess I should instead ask for reference material on that.
KJ3N
10-02-2010, 10:33 PM
I thought 5/8 waves had a higher angle than 1/4 waves?

Nope. Pages 5 & 6 (http://ndl.ee.ucr.edu/manual.pdf).
KC2UGV
10-05-2010, 08:38 AM
Nope. Pages 5 & 6 (http://ndl.ee.ucr.edu/manual.pdf).

Thanks :) That whole doc is some good reading there.