Richards wrote:
> Good Day Tower Talkians --
>
> I am trying to select an antenna to install before the winter arrives.
> I live in Michigan, and have a smallish, 100' (N-S) x 55' (E-W)
> suburban backyard that has a bit of a hill in the back, and a
> trough towards the house and back deck. Cost is not a limiting
> factor. Wife says a tower is OK - and would rather have a tower
> than have holes in the roof. City says tower based antenna can
> be 55 feet tall with no need for permits, or inspections, carte blanche,
> but higher will entail fighting City Hall.
It would be nice if they would give you that statement in writing (not
about the fighting, but that no permits are needed).
Wife would like to avoid large
> radial ground wire field, but understands it might be necessary.
I would think that you can do the radials in a way which is invisible
and of no impact, unless you have a field that you're regularly tilling
to some reasonable depth, so the wires would get dug up.
>
> I now have a 40 M half wave dipole, and an Alpha Delta DX-EE
> multi band, trapped dipole covering 40-20-15-10- etc.
>
> What I am considering most are:
>
> * DX Engineering 43 foot vertical / Force-12 43 foot Vertical
> * Hustler 6BTV / or Butternut HF9V
> * HyGain Hi-Tower ACV 18
> * HyGain AV-640
>
<snip>
> So.... any ideas? Have I missed any reasons to consider one more than
> another? Have I missed any pros or cons for any of them? I know I might
> just as well put up a SteppiR Big Vertical, but that costs $800 - $1000
> fully installed, and you must wait 5 to 7 months to get one, and I want
> something up NOW before the snow flies. If I put one of the models that
> require a field of ground radials, then I can substitute a Big StepplR
> for it at a later date, maybe next summer and use the same radial plate
> and the wires can work for whatever I mount to it.
>
How much power are you running? Just the 100-200W from a barefoot rig,
or do you run an amp?
A couple general comments:
1) There's no such thing as a "ground independent" vertical. The radial
field is important: for the traditional vertical, it's the other half of
the antenna; for the elevated vertical dipole (whether off center fed or
not), the radial field improves the apparent soil conductivity, reducing
losses in the near field. (same thing for horizontal antennas, too,
really.. it's more a "low antenna" thing)
2) whether you get your impedance matching by loading elements in the
antenna or matching networks at the base or somewhere else, the actual
effectiveness as radiator is pretty much the same. Putting in a
loading coil will change the current distribution a bit, and will have a
*small* effect on the pattern (which is almost totally dominated by the
interaction with the local soil). Sure, there's a difference between a
6 foot and a 20ft radiator, but there's not a huge difference between a
20ft and a 30ft.
3) For simplicity, I'd go with a unadorned vertical mast of some sort,
with a SGC tuner at the base. The bottom of the line tuner is about
$150.. the losses in that tuner are comparable, if not less, than losses
in traps, etc. Choose your vertical length carefully.. there are some
"bad" lengths (close to 1/2 wavelength on some band) which result in
very high feedpoint impedance, which results in more loss in the
matching network (or loading coils/traps). The other thing is that an
antenna that is "long" compared to a wavelength (e.g a 40 foot mast on
10m) is going to have a lot of weird lobes in the elevation plane.
4) The next step up in complexity might be some sort of elevated feed
dipole (with a tuner at the feedpoint). That lets you run shortish
elements (so you don't get the weird lobes), gets the high current part
of the antenna farther from the (lossy) soil. I've been playing with
the idea of something like a 20 foot long elevated dipole, with the
feedpoint, say, 25 feet off the ground.
5) The 6BTV seems attractive at first, because, in theory, you don't
need the tuner, but in reality, adjusting it is a pain (hours of work),
and it winds up being pretty narrow band on 40 and really narrow on
75/80, so you'd need the tuner anyway. That said, I used exactly that,
with an LDG auto-tuner in the shack, and didn't bother spending much
time tuning/adjusting the actual antenna. With 50 feet of transmission
line, the losses just weren't that huge, even if the antenna's resonance
was at, say, 13.95 and I was operating at 14.2
Jim, W6RMK
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