A Question for the Antenna Gurus

[W3WN]

OK, an idle thought crossed my mind as I was working on the front porch tonight, and I wanted to run it by the antenna gurus out here.

As you may recall from an earlier thread, I am going to be putting up a flag pole vertical sometime this summer, as part of the front porch remodeling project. And it's not a question of "if" but "when" -- the fiberglass flagpole is sitting in the house waiting for the right point in time in the project.

Since it's a fiberglass pole, obviously I'm going to be running a wire up inside it, approx. 21 - 22 feet; the length of the pole is 22 feet, I'm not sure if I'm going to run the feed out above or through the mounting post yet. And it's going to connect to an SGC tuner mounted right at the base, so loading should be relatively easy (famous last words).

Now, the idle thought is simply this... why not run more than one wire inside? That is, run multiple lengths cut for each band (10, 12, 15, 17, 20 & 30 meters) alongside the "main run". This ought to make the flag pole resonant (more or less) on each band; or close enough that the tuner won't have to "work" too hard to match.

For this to work, it would have to be insulated wire. The main length would also be the vertical support. Of course, everything would be tied together at the main feed point. And it should go without saying that there will be a nice radial field laid out underneath the antenna (including underneath the deck that's going to go over the concrete porch) so that shouldn't be a factor.

The theory is that, as implied by Ohm's Law, energy should flow to the most resonant wire on a given band, as the path of least resistance. And I'm confident that this should work, recalling the mobile antenna setup I had on my old van -- 2 Ten-Tec mobile antennas (their short-lived clones of the hamsticks) on 40 & 15, plus a 10 meter whip (OK, a CB whip trimmed), all in parallel on one feed. Three bands, no switching, no tuning (which was nice considering that the TS-120S I ran mobile at the time didn't have a tuner built in!)

And I will try to borrow an antenna analyzer, trying to cut the wires as close to resonance as possible.

Thoughts?

[KG4CGC]

I've considered similar ideas and some say that the proximity of the wires together may upset the balance of Space Time. Kind of when you use a fan dipole. Why does it have to have spreaders? Why can't the wires just be closer?

Just for your own sanity, make it easy to disassemble so you can get to the insides any time you need to. There may well be quite a bit more experimentation than you are bargaining for.

Is there something you can put on the end of each wire so that it will truly be easier on the tuner? Half wave inductor? I dunno at this point but if a bicycle wheel reflector can work on VHF ..........................

[W3WN]

I've considered similar ideas and some say that the proximity of the wires together may upset the balance of Space Time. Kind of when you use a fan dipole. Why does it have to have spreaders? Why can't the wires just be closer?< snip >

Might be because you can't put bare uninsulated wires too close together?

[KG4CGC]

Might be because you can't put bare uninsulated wires too close together?

No no no ... has nothing to do with that. To be clear, I use insulated wires on every antenna. My understanding was that it is an issue of resonance and proximity. If there was not an issue there, I would have made a multi-band dipole last year but months of questioning led me away from a non spreader fan dipole.

If I have misunderstood this particular issue then I might take something down, call it a mulligan and rework it like so much (insert appropriate adjective, noun and adverb)

[NQ6U]

I've seen that done with dipoles ("fan dipoles") but I don't know what will happen with a bunch of 1/4 wave verticals; in such close proximity, I'd expect them to interact with with each other and mess with the tuning/radiation pattern. More typically, one vertical antenna is used with an adjustable loading coil on the bottom. But WTF, it seems like it's worth trying since you're putting the whole thing up anyhow. The worst that could happen is it won't work and you'll have to pull out the extra wires but, who knows? You could end up with something awesome. For instance, a club buddy and I were playing around yesterday and came up a 20m Moxon built out of 1/2" copper plumbing pipe that can be disassembled and tossed in the back of a short-bed pick up for Field Day. No worse than 1:1.5 SWR across the entire band and our first on-air test—with 100 watts and the thing less than six feet off the ground—resulted in a S-9 report from a ham in New Jersey.

[W3WN]

< snip >More typically, one vertical antenna is used with an adjustable loading coil on the bottom. < snip >

Well, that's pretty much what I would have with the SGC tuner.

But hey, it's worth a shot. What do I have to lose, some wire? Anything I pull out can get converted to radials anyway!

[WØTKX]

Prolly be amusing to play with antenna modelling software, if you do that.
They will interact, but you may find it useful.


What about simply running multiple wires the full length as in a cage dipole?
But you know, like half of one. Fat and tubular to RF.

[W3WN]

Prolly be amusing to play with antenna modelling software, if you do that.
They will interact, but you may find it useful.

What about simply running multiple wires the full length as in a cage dipole?
But you know, like half of one. Fat and tubular to RF.

Any suggestions on a software app to look for?

[WØTKX]

Any suggestions on a software app to look for?

I play around with an earlier free version of EZ-NEC. It's pretty limited, but something of a standard out there. I don't know if the free/trial versions would model what you are trying to do. Might be worth trying.Maybe add a big brass eagle on top as a "capacity hat"?

[PA5COR]

Known as the "cat whisker" antenna, mostly as dipole.

The several verticals will interact with eachother, but it can work, you need to tune each vertical to the right sweet spot, while they interact that will be a hassle, but it can be done.
Using a coil at the feedpoint you could even cramp 80 in there, though with a smaller bandwidth.