Cubilcle Quad Antenna

[pkveazey]

Oh, No!!!!! Last night I was listening on 440 Mhz and using my Home Brew 440 Cubicle Quad antenna. The band was fairly open and tropo was giving me some extra range. The Quad was pointed due North, straight into downtown Richmond, Va. All of a sudden, I started hearing repeaters in Raleigh, NC. My first thought was, "Uh Oh, I outsmarted myself. Instead of spacing the reflector between .15 to .20 wavelengths behind the driven element, I placed it .25 wavelengths. The antenna works great in the direction its pointed and it rejects signals off to the side. However I put the reflector a little bit too far back and I don't have much rejection to the rear. The spacing has an effect on gain but if you go for max gain, you can lose the rear rejection. Yep..... That's exactly what happened. I have a 1/4 wave ground plane at 40 feet and the Quad at 30 feet. The quad can bring up and talk to repeaters that the 1/4 wave ground plane can't even access. Am I going to change it? Nope, but the next Quad I build will have .15 wavelength spacing.

[JohnyMac]

Do you have a picture you could share?

I have been using a Moxon antenna with great success in 2 Meter.

Funny story: I blew our my 1/4 wave ground antenna so I bought a Comet GP3 VHF/UHF antenna. With the help of my neighbor, in a snow storm, we finally got it up. Went in to try the BIG repeater located about 30 miles south of my cabin and.....I could ping the repeater but couldn't hold it.

Sent a email off to Comet and they instructed me to rotate the antenna extension 90% as I was in a "null." Well MrsMac will not let me go back on the roof to rotate it. DAMN! Still using the Moxon that cost me about $3- to build. 

[pkveazey]

 :bravo:I don't have a picture of the 440 Quad and if I did take a picture it wouldn't be much help because a 6.5 inch square antenna up at 30 feet would be tiny in the picture. I'll try to draw a picture using PAINT and post it. The only thing that is metal in the antenna is the wire. Capacitive coupling to close by metal can really be a monster.

My 2 meter antenna is a 6.5 db gain, Diamond CP22 (5/8 over a 5/8 wave) at 50 feet. I bent the radials down a bit to improve it. I can hook up the 5 watt HT to it and bring up at least a dozen repeaters within a 50 mile radius. Even though its not a dual band, I've even used it on 440 and it works great and the VSWR is still low. Since then, I've built dedicated 440 and 220 antennas installed at 40 feet.

Your null problem might not be the type of null you are thinking about. A null between the radials is usually not very severe. Just moving the location a couple of feet in any direction might make all the difference. If you can't change the location, then try to raise the antenna about 5 feet. Either of those can make a dead antenna come to life.

OK, I'm off to draw a picture of the way I constructed the Quad for 440.

[JohnyMac]

Thx for the pic PKVE.