800mhz gain antenna

[Hoofy]

I just built one of these 800mhz gain antennas for my pro 2096.

http://www.angelfire.com/extreme/sideband/collinear.html

I used the numbers for 867.mhz and adjusted the equation to use LMR 400 coax. I put it in a piece of pvc and capped both ends. I did drill a hole in the bottom cap first so I could bring the coax end out. It did an excellant job on 800 but the vhf and uhf freqs suffered.

I added a T connector to the bottom of the coax where it comes out of the pvc and connected my feedline to the side of the T. I then took a Larson 5/8 wave 2 meterwhip with base and unscrewed it from the mag mount and attached it to the bottom of the T connector and hung the thing up in my attic. It's about 10 feet high. The feed line was a piece of 9913 I had saved.

I'm sure I broke a lot of rules and theories and it's kinda weird looking but it works really well for a scanner antenna. I used the 4 1/2 wave sections for mine.

No, I don't have any photos. You'll have to visualize it.

 

[kb2vxa]

Hi Hoffy and all,

Have you ever heard the song that goes "I broke the law and the law won."? Assuming the antennas are colinear, that is one directly above the other at least you haven't made a directional phased array. Then again you may experience signal loss on some frequencies again due to phasing problems, this time due to the differing antenna and feedline wavelength relationships on any given frequency. That's hard to explain in English but neither of us understand those funny looking Greek letters in the math. You did however louse up the impedance match but because you're receiving only it probably won't matter much.

Oh, that 2M antenna requires an electrically continuous ground or it's just a piece of wire, is the sleeve connected to the T or just the center pin? Where's the ground plane? It also requires a counterpoise or it's only half an antenna.

Hey, whatever works, if it does we may consider hiring you as a design engineer at Frankenstein Laboratories, a division of Altec Communications. (Scott W2SJW is probably laughing his butt off.)

 

[Hoofy]

I told you I broke all the rules and theories but it works very well for what I want. No, there is no ground plane or counterpoise. I am getting 800mhz from 50 miles and aircraft from over Duluth and who knows where on the civilian aircraft. Also picks up all other vhf signals that I want to listen to.

That's why I always encourage people to experiment. Especially on antennas that are for receive only. There's a satisfaction that comes with building something and having it work.

 

[kb2vxa]

Hi again,

Like I said, whatever works, now submit your resume.

 

[Hoofy]

comparison test

The other night was a quiet night for scanning around here so I decided to try a comparison test.

I have a dual band Diamond vertical. I don't remember the exact model number but it's a 510 something with a so-239 at the feed point and a claimed 8 or 9db gain. It's mounted on my tower and the top of the antenna is up about 90 feet. Feed line is LMR-400.

I went thru my 2096 and checked the decoding percentages on all the MPSCS 800 cc I could get while the 2096 was connected to the homemade 800 hybred gain antenna I have in the attic. which is about 40 feet above ground. I then connected the Diamond antenna to the 2096 and actually got better readings from a couple of cc. Because of no signal strength meter I couldn't tell how the vhf was coming in but it seemed to be at least as good as the hybred.

I'm going to test it periodically under different weather conditions and see if it is still performing well.