Loaded 160m dipole

[KB1CKT]

I've been musing about what to put up for 160m; at the moment I'm not sure if I want to go the route of a vertical. I mean, I want the vertical for DX but between "lots" of 100'+ radials and figuring out height... Maybe a simple low dipole. Nothing wrong with trying something out and replacing later I figure.

I realize loading coils "eat bandwidth" and whatnot; but right now I think a 160m dipole would wind up with feedline dropping awefully close to my 6BTV--which I don't want to mess with, since I'm happy with its performance. Anyhow, doing various searching I came across this, which is intriguing:

http://forums.qrz.com/showthread.php...21#post1887921

The poster has a drawing showing a loaded dipole, 64' on leg, with a coil at 32'. My question is, would the high inductance of the coil really allow dual band operation? I'm wondering if this could really work on 160/40 as drawn (and then an 80m dipole added in for good measure). Traps require capacitance across them, to form a parallel resonant circuit, so as to "trap" RF on the desired portion; I get that--this isn't a trap therefore, just a large inductor. Going to K7MEM's website, I find that it's about 82uH, which at 7.1MHz is +3700j ohms; but this trap would be at a high impedance point on the antenna so I'm not sure it would actually work (if it did, I'd probably see 160/40 dipoles for sale as such). Although, if I'm doing the math correctly, I come up with 6pF to resonate this 82uH inductor on 40m--which I'm guessing is less than want the coil would have.

[KB1CKT]

Oh, and I know that really, I need it to be up higher. And preferably not on the house. But this is what it is, though.

I might be able to pull off some sort of horizontal loop; I have a half-acre of woods doing nothing. Doubt that I could suspend more than 30' or so, maybe 50 if I'm lucky (need that sling shot!) and I don't know how I'd want to run feedline back (remote tuner and coax would be nice, I guess). I wonder what coupling to the power lines would be like though (less than 100', maybe, and in parallel?). Plus, as the loop goes up, it becomes more problematic getting the wires around the tree branches, I'd think.

[KB1CKT]

Oh--looks like maybe Alpha Delta is doing just that. Wicked narrow on 160, but that's not that surprising. Not cheap for their antenna(s) though. Maybe the concept is valid afterall.

[N3OX]

if I'm doing the math correctly, I come up with 6pF to resonate this 82uH inductor on 40m--which I'm guessing is less than want the coil would have.

Yep, I think there's a good chance that the coils can be made to self-resonate on 40m, especially if insulated wire is used.

Oh--looks like maybe Alpha Delta is doing just that. Wicked narrow on 160, but that's not that surprising. Not cheap for their antenna(s) though. Maybe the concept is valid afterall.

You should be able to juggle exact wire lengths to get dual band resonance even with a "pure inductor" load, but once you get into the range where a handful of pF resonate the coil, that's probably not how the antenna is working. I don't know about Alpha Delta, whether they're using self-resonant coils or ones that behave more like pure inductors.

I mean, I want the vertical for DX but between "lots" of 100'+ radials and figuring out height...

Don't let small support height or a perceived need for "lots of 100'+ radials" scare you away from using a vertical or inverted L.
You would probably need single-ground-rod levels of ground loss before a 30 foot high dipole would routinely (not during special high angle propagation) be competitive with an inverted L with a 30 foot vertical section for transmitting on DX. The dipole would never beat the inverted L for DX reception because the pattern of the inverted L is so much better.

On the higher bands a dipole can be competitive with a vertical for DXing, but when you're talking about a dipole five-hundreths of a wavelength off the ground, a vertical or inverted L is going to smoke it. An inverted L will work okay for local stuff too (a straight up vertical will suffer when you try to work close-in, but will be better for listening to DX). Not trying to scare you away from the dipole or anything... go for it. But don't assume the dipole is a better choice if you can't put in a massive radial field. An inverted L with a pretty minimal radial field would be way better than a dipole in most conditions. For a quick test without installing a big system, you might try trimming four or six radials to on-ground resonance, like in here:

http://rudys.typepad.com/files/qex-g...ems-part-2.pdf

Bad antennas can work okay on 160 especially for us East Coasters. I have a 60 foot base loaded vertical and a radial field of about 30 radials that mostly fit in about a 50 foot diamond shape (estimated 12 ohms of ground loss) and I worked 116 countries on 160m with 100W and I'm up to 135 (I think) with about 400W (not necessarily needed... I just started running an amp at the 116-worked point.) Best DX is VK and ZL so far. I probably can't make it through to 9M2AX on 160m but I've never heard him either, so that's a bit moot

[KM1H]

Yeah, but it was easy with full size phased wire verticals, elevated radials, 1200W, and a Beverage.

Carl

[KB1CKT]

I'll keep that all in mind. At the moment I'm starting to think dipole as it's less work--I spent 20 or 22 hours on my 6BTV over several weekends, and I still need to go out and tune 40m a bit, and think about those guy lines. Am starting to think I don't want to repeat this *and* have to make the antenna too.

[KR2D]

What kind of radial field is installed for your 6BTV? If it's wire on/in the dirt, you can share that with an inverted L.

I have a Butternut HF-2V with 16 ground radials ranging from 23 to 75 feet in length (ran them until I hit something or the piece of wire ended). My 160m antenna is a inverted L composed of 150 feet of wire tossed over a nearby tree that is 50 feet tall. The feed end connects to the feedpoint of the HF-2V with a quick disconnect. I tune it from the shack with a MFJ-949E.

[K8JD]

I have worked some fairly nice European DX on 40 and a few countries on 80 with a HF6v vertical and just a few radials with my 100 W.
I have considered trying a vertical on 160 but just too much trouble and copper expense for all those radials.
Instead I put up a halfwave dipole and worked most of the US and Canada, except for HI and AK, with it and the 100 W.
Plenty of DX on the higher bands that I still am trying to catch.
It's good enough to work my neighbors in N.A. on 160M

[G0GQK]

May I suggest an inverted L, the vertical section as high as possible. Do some Googling, 132 ft is about the length if my memory is still OK

[K8JD]

May I suggest an inverted L, the vertical section as high as possible. Do some Googling, 132 ft is about the length if my memory is still OK

That would be for 80M unless you add a huge loading coil.