Dueling Di Poles

[SOL1776]

I'm thinking of putting 2 diploes on opposing ridges on my house does anyone know that if crossing them would affect performance?

[goofy]

It probably won't hurt, and could actually help.

The runs of cable in from the dipole to wherever they meet should be 75Ohms not 50 (just like the two sides of a phasing harness in a dual antenna vehicle setup).

The part of your house that is between both dipoles might affect matching a little bit, so it will be good if the antennas are tunable.

[drdx]

Put them perpendicular to each other. I've seen that recommended in antenna books. Dipoles are bi-directional and that gives you full coverage. You can cross them with no real ill effect. In fact, if you operate in several different bands you can use the same dipole center and have more than one pair of legs on the same center insulator. The legs with the best match will radiate and almost ignore the others. You will have some interaction but if you space them then it is doable, especially with a tuner.

-drdx

[231]

Yea, that's all dual polarity yagis are on the driven element. You can either phase them or use a switch box and select which you want to run.

Have fun...I was going to do the same thing on my station just haven't gotten around to it.

[SOL1776]

Yea, that's all dual polarity yagis are on the driven element. You can either phase them or use a switch box and select which you want to run.

Have fun...I was going to do the same thing on my station just haven't gotten around to it.

Thanks...I was thinking of using a switch, are there any advantages of phasing?

[231]

Thanks...I was thinking of using a switch, are there any advantages of phasing?

No, just omni direction vs. bi-directional. That's why I wasn't going to phase mine...just stick them up opposing and use a switch box (I have a remote switch box at the bottom of my support structure). But a switch box inside can be used inside the shack as well, it just means two individual feed line runs is all.

[SOL1776]

Thanks for the help guys, I started putting them together today so I better hurry up and get a radio!!

[goofy]

Small benefit to phasing to dipoles, will get more gain, (and more headache) as you phase in more.

That's where the whole science of phased arrays comes in

[SOL1776]

Small benefit to phasing to dipoles, will get more gain, (and more headache) as you phase in more.

That's where the whole science of phased arrays comes in

Guess I'll have to do a bit more research on phasing, sounds like it may be worthwhile....

[SOL1776]

Got my dipoles up and running! They cross a couple feet from the ends and I set the N/S a couple feet higher than the E/W (will post pics if anyone is interested) Have an swr of 1.1!

[Lost Ram]

Pics would be great!!!!!
Co-phasing will only help if the person you are talking to is the same way as you. If you talk co-phased to a person that is not there will be a 3db loss. The only time I find it useful to run my beam co-phased is when I am scanning (listening) for good skip. Once I find it i use the polarity they are using, its obvious by the signal strength. Sometimes the signal gets flipped when talking skip, I talk skip to some that are on ground planes but we get better results when I am on the flat side. You can buy an antenna switch with the co-phasing built in so you dont have to run 75ohm coax. It is fun to work them in different modes and experiment with them.

[SOL1776]

Thanks for your input on phasing I think I'm goin to leave them switched and may build a ground plane for local and scanning.
I'll get some pics as soon as it stops raining.....

[SOL1776]

Finally stopped raining in Assachusetts I'll get pics up tomorrow!!
Thanks to everyone for their input!

[Lost Ram]

Kewl!!

['Doc]

Just some stuff about 'phasing' antennas.

There has to be two or more antennas to do any 'phasing', and those antennas have the same basic requirements as any single antenna. They should both be resonant and have a usable input impedance. Resonance deals with the absence of reactances in an antenna, which just don't contribute to radiating anything. The input impedance ought to be such that when combined with the feed line's impedance the result will be something the transmitter will be able to use (typically 50 ohms) without any significant problems.
So, what's the advantage of 'phasing' (timing) antennas? It can make a difference in directivity, and by how the fields are combined some gain can be realized in particular directions (always at the expense of having less gain in other directions). So making the thing directional to some extent, and raising/lowering radiation angles to some extent. If those qualities are desirable in your particular situation, then it's probably a good thing to try.
The PITA part is the impedance matching. It is never simple, and takes some understanding of what resistance and impedance is in relation to alternating currents. Another one of those things to get around is reactance, or how stuff 'reacts' to varying currents, etc, etc. DC circuit resistance, voltage, and current is NOT like AC resistance, voltage, impedance, and reactance. Big differences, and confusing, but certainly not impossible to understand. Sometimes it takes longer for that 'light' to turn on for some than for others. Just keep banging your head against that wall, it'll break down eventually. (Aspirin and beer helps.)
Phasing antennas is much easier for 'fixed' antennas than for 'mobile' ones. It just means one less variable in how/where to point the @#$ thing, or to keep it pointed in the right direction.
There's a lot more to it than just this, it's really sort of complicated. Phasing is certainly one way of improving things, but it only 'fits' easily in particular circumstances. If it 'fits' your situation, use it! If not, it just ain't worth the trouble.
Ain't all this 'stuff' fun??
- 'Doc

[SOL1776]

Hey Doc thanks for the info on phasing, I think that will be the next "phase" of my dipole experiments....here's a couple pics taken from the ground so the perspective is a bit skewed. I'll get some better ones next time I'm up there...



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[Lost Ram]

Thats great! The wealth of the knowledge gained from making your own antenna is awesome!!!! Antenna building really enhanced my radio hobby experience. My MFJ antenna analyzer was also a great help as well. When you co phase try this product (Dosy SW-4, 4 Position ). Its allows you to still use your 50 ohm cable, I use one for my Maco Shooting star beam. It works great for me.