Topband: New TX antenna for 80 and 160?

Dan Simmonds dan at kk3an.com
Mon Dec 3 01:37:30 EST 2012


Hi Rick,

I've been down this same road as you - starting with a low (18 metre) 
dipole, and after 1+ year of using it, I was only able to copy & work 
just (1) DX station from here in the Northeast US - that being DF2PY.
I couldn't even work to the west coast of the US with the low dipole. 
Later, I replaced this dipole and installed an Inverted L with just (3) 
radials and worked lots of DX straight away - including VK / ZL. The 
difference between antennas was immeasurable - it was really that good.

If you can manage just (1) bent radial with your Inverted L, it will 
still beat the low dipole if your interest is DX - especially at your 
QTH near the ocean. It won't be optimum, but it will work for you - and 
with just one radial you'll probably have 150-200 Khz of 2:1 bandwidth 
on 160m.

Your questions:

1) Yes
2) I use a single 10 gauge copper clad wire for my "L". Even heavily 
loaded with ice every winter, I've never noticed this wire stretching in 
4 years of use. Takes full power easily.
3) I have no experience with a Spiderbeam.
4) My Inverted L is fed direct from 50-ohm 7/8" hardline - no matching 
network whatsoever. 1:3 minimum SWR at resonance.

73, Dan  KK3AN


Rick Kiessig wrote:
> Until recently, I was planning to put up an inverted-L as a TX antenna for
> 80 and 160. However, things have changed, and it no longer looks like I'll
> be able to run the radials I would need to have an effective vertical. Now
> I'm leaning toward a low dipole.
>
> My site is highly constrained: it's near the top of a ridge, on a slope,
> facing the ocean (100m above sea level, 300m from the water). The highest
> spot above sea level is the top of my tower: it's only 8.5m above immediate
> ground level (next to the house), although the ground 10m away is 7m lower.
> I can't run more than a wire or two and a coax feed on (not above) the
> ground - an FCP, for example, would be much too large. Due to limitations
> imposed by the city, I can't go higher than 10.5m above ground level.
>
> If I run a wire around three sides of my property in a U shape, hung from
> the tower near (but not at) the feedpoint, I can just hit 80m total length,
> with a 46m long center section and two 17m long end sections. The wire would
> attach to 10m high fiberglass poles near each of the four corners of the
> property.
>
> I recently built a dipole for 40/20/15 using 300 ohm twinlead, which worked
> out very well, so I'm thinking of using a similar approach for this antenna,
> using the full length for 160, and trimming one wire to be resonant on 80.
> I'd like to do whatever I can to maximize bandwidth. If I could cover both
> 80 and 75, for example, that would be great.
>
> Questions:
>
> -- Is a low dipole for 80 and 160 on a sloping site like mine worth the
> effort? I'm interested in DX, not NVIS.
> -- Given my constraints, are there other types of TX antennas I should
> consider?
> -- What's the best wire to use to minimize stretching and to maximize
> bandwidth and efficiency, and that can handle full legal power? I will need
> at least two (maybe three?) wires to cover both bands. Copperweld is strong,
> but I've heard it can be lossy, too. Twinlead has two wires, but it's
> stranded and doesn't feel very strong.
> -- I'm thinking about using Spiderbeam black fiberglass telescopic poles at
> the corners. However, I'm concerned about durability in high winds and
> having enough strength to be able to tension the wires so they don't droop
> terribly. Is there a better choice?
> -- I'm planning to put a common mode choke at the feedpoint and run coax
> from there, as I've done with the other dipole. Any reason to do it
> differently?
>
> 73, Rick ZL2HAM
>
>
> _______________________________________________
> Topband reflector - topband at contesting.com
>
>   



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