Dipole help

[Falkon MX-5]

I've been working on a dipole antenna comprised of two 102" whips. Well, I've got it built, but I can't for the life of me get that SWR below 3:1. Unfortunately I cannot raise the antenna up any higher. Would it benefit me to use 108" whips or cut down a 12-meter tuned hamstick?

[Phaze91460]

Dont know much about dipole antennas but the ones I have seen are a precut wire streched out in a v or L pattern. Length looks like cut for SWR, dont know how you would cut whips.

what SWR do you get with just 1 whip hooked up ?

[Falkon MX-5]

With one whip, SWR would be pegging the meter Think of the same antenna you have on your mobile. The ground plane is your car chassis. In this case, it's the other whip.

[Phaze91460]

k, so one whip is attached to the ground at the cable or mount ? Does that make it directional ? Is the Vert whip strait up and down ?

[Falkon MX-5]

They can be either straight up and down or horizontal. One whip is going one way and is attached to the center conductor of the coax. The other is attached to the shield and is going the other way.

[Falkon MX-5]

I think the Radman knows his stuff. I've been trying to enlist the help of a few hams. As I'm reading, it's looking like I might need something called a balun.

[Falkon MX-5]

Inverted vee, on the mast and in the air! On the air too!

[HI-TECH]

what you need is a little tool called a balun (ballanced+unballanced) for it to work properly... you dont nesassarly need it but it helps you to get a better swr

[Rex_foxhound]

:06-23tti:

It would help me understand a little better though. lol

[jcollins]

:88-roulette:

[Falkon MX-5]

what you need is a little tool called a balun (balanced+unbalanced) for it to work properly... you don't necessarily need it but it helps you to get a better swr

Yeah, I made a po' man's balun by wrapping some coax around a PVC pipe at the feed line. I took it off for now. I need to adjust my whips in a bit for better SWR. I SHOULD be able to tune close to 1:1 with the right lengths. I'm sitting at around 1.5:1 at channel 1 and close to 2.8:1 at 40... about 2:1 at channel 19. So I need to bring it in some. It's a hassle to get that thing up and down, but it's totally worth it. Even with high SWR, the height just lets me get everything.

As for wetting the ground, many people put bentonite [found in certain kitty litters] and put it around their towers. It soaks up and holds moisture. For this, I don't need to do that.

A ground plane antenna is just a dipole with 4 radials going out at 45 degrees instead of one going straight down.

I'll get pics soon. I took a crappy one with my phone cam, and I'll post it up.

[Phaze91460]

I think I asked this before but, what the heck, Is a dipole a directional antenna ? Stronger in the direction you point the ground end ?

[Falkon MX-5]

Nope, dipole is PRETTY much an omnidirectional. Your antron is a dipole. It just uses another method where the physical earth ground acts as a mirror antenna.

There's a horizontal and a vertical dipole. The difference is which direction you have it turned. Of course for CB you want vertical. Vertical antenna = vertical polarization. Horizontal dipole = horizontal polarization. Horizontal polarized signal being received by a vertically polarized antenna = dB loss!

Okay, think of a 102" whip. That 102" whip is connected to the center conductor of your coax through the mount. Well, where does the shield of the coax connect? To the mount itself of course! and where does that mount connect? To your truck bed or roof or anything. So that metal body is acting as the ground plane, so it's like another 102" whip was on the ground side.

Now, take that whole mount off the truck, suddenly the SWR is through the roof! There's no ground plane! So, take another 102" whip, this time pointing down, and connect the shield of the coax to it. Now, you have one whip going up, one going down, and you have yourself a vertical dipole. Now, you just need to stick it way up in the air.

I hope that's a good explanation.

Now, you know those ground plane kits you can get for your antron? Those are just radial antennas coming out. I'm not sure why, but the best performance is had with 4 radials, that's why the ground plane kit gives you 4 antennas. Make sense?

I've crammed a ton of antenna theory into my head. I've played with making inverted vee antennas, dipoles, and jpole antennas. Now, I just need to get it all tuned right!

Oh, did you know you can pretty much make an antenna with two wires?

[jcollins]

that is what my inverted v is made of wire
with a balun swr is great with the right length of wire
jon :Peace!:

[Phaze91460]

yup, thats the only way I have seen um before.

I take that back, I saw one made with 1/2" copper plumbing pipe.

[Falkon MX-5]

Here she is in all her glory!

[Falkon MX-5]

Yes, that is an extension pole.... I got the idea from another guy who used to do portable communications for a living.

[BobOstro61]

Very cool! Can you make me one!

[Falkon MX-5]

I'm working on tuning mine right now. I've got it down to 1.5:1 SWR, but I really need a grinder to shorten the whips to get lower.

Great thing about the inverted vee is I believe it's circular polarization, meaning it's good for both local and DX use.