Mobile antennas in phase quadrature

[995]

Anyone ever done it successfully?

I tried a while back but could never get the tuning down. I suspect that my coax length was flawed (wether it was measuring, cutting, or doing the math). I went back to the single reflector. I may try again with some fighting sticks instead of the 'round town antennas.

 

[Toll_Free]

Anyone ever done it successfully?

I tried a while back but could never get the tuning down. I suspect that my coax length was flawed (wether it was measuring, cutting, or doing the math). I went back to the single reflector. I may try again with some fighting sticks instead of the 'round town antennas.

Yes.

The trick is this: You don't have enough coaxial cable to reach from one antenna to another when you take velocity factor into it. So, to get the phased array to REALLY work, you need to feed one antenna with a 3/4 wave phasing harness, and another with a half wave phasing harness.

There, the trick is out of the bag on phased arrays for CB use.

Don't, DON'T forget the velocity factor. That's the numero uno factor.

Phased arrays = more back door than forward gain. Don't get confused with max forward gain and max backdoor. They are NOT the same, and your max forward gain happens almost when your backdoor looks like a dipole... ie, NO BACK DOOR.

--Toll_Free

 

[Master Chief]

when your backdoor looks like a dipole... ie, NO BACK DOOR.

No confusion here!

 

[995]

You don't have enough coaxial cable to reach from one antenna to another when you take velocity factor into it.

I have seen folks do this with as little as 1/8 wave spacing between the two antennas. Not saying I agree with that practice, but with that spacing, you could have enough coax. I cannot imagine the gain would be anywhere near what it could be with 1/4 wave spacing.

Don't, DON'T forget the velocity factor. That's the numero uno factor.

Of course not..you couldn't even begin planning this setup without thinking about VF.

Phased arrays = more back door than forward gain.

Backdoor = F:B ratio? If so, then of course, that make sense. Never heard "backdoor" in this context.

So, to get the phased array to REALLY work, you need to feed one antenna with a 3/4 wave phasing harness, and another with a half wave phasing harness.

This is where it get's really tricky. You kinda confused me with the "phasing harness". I have never seen a two antenna system with more than one "harness". Anyway....what coax is the question. Most folks say 50 ohm for the whole setup. I do not see how that could work....and when I tried it, it didn't.

Here's what I have been thinking about experimenting with:

The length of coax (3) could be varied from 0" to 1/2 wavelength, changing the phase andwhere from "co-phase" all the way to 180 out of phase.

 

[Toll_Free]

You don't have enough coaxial cable to reach from one antenna to another when you take velocity factor into it.

I have seen folks do this with as little as 1/8 wave spacing between the two antennas. Not saying I agree with that practice, but with that spacing, you could have enough coax. I cannot imagine the gain would be anywhere near what it could be with 1/4 wave spacing.

Don't, DON'T forget the velocity factor. That's the numero uno factor.

Of course not..you couldn't even begin planning this setup without thinking about VF.

Phased arrays = more back door than forward gain.

Backdoor = F:B ratio? If so, then of course, that make sense. Never heard "backdoor" in this context.

So, to get the phased array to REALLY work, you need to feed one antenna with a 3/4 wave phasing harness, and another with a half wave phasing harness.

This is where it get's really tricky. You kinda confused me with the "phasing harness". I have never seen a two antenna system with more than one "harness". Anyway....what coax is the question. Most folks say 50 ohm for the whole setup. I do not see how that could work....and when I tried it, it didn't.

Here's what I have been thinking about experimenting with:

The length of coax (3) could be varied from 0" to 1/2 wavelength, changing the phase andwhere from "co-phase" all the way to 180 out of phase.

Quickly, im out the door.

Backdoor = F/B ratio... In CBer terms.
Your wiring harness you posted in the picture is exactly what I was talking about.

And yes, an 8th wavelength will give you f/b, but very LITTLE forward real gain.

I have the hardest time convincing people that front to back ratio and forward gain are independant, and usually opposite of each other. At least you seem to already know something of antennas. Makes things easier


--Toll_Free

 

[995]

Toll Free, thanks for the comments. Just so you know...I'm not looking for spectacular gain. I just want to see it work. Kinda like a science project. Surprised there wasn't more interest in this post though.