Hi All,
I would question the assertion that a resonant dipole is the
absolute best choice. First of all, I think the original
query included the condition that the antenna needed to fit
within "the footprint of the campsite". Now, we don't know
how big that footprint is, but I can certainly envision that
such a footprint wouldn't be that big, particularly in a
crowded campground. Putting up a resonant dipole there
could easily be a problem.
I would concede that a resonant dipole alleviates lots of
"issues". But conditions at hand don't always make it the
best choice. A dipole that can only be elevated a short
distance is going to be pretty "NVIS" as a general rule.
Perhaps that's sufficient, but generally it isn't. If you
can get it up in the air a fair amount, all the better.
Furthermore, if you use balanced feeders and a tuner, you
have the makings for a nice little multiband system. But
again, you may not be radiating in all directions very
effectively, so maybe that's a problem too. But clearly a
dipole that you can elevate somewhat is a good choice.
I find vertical systems to be quite beneficial in many
situations. True, there may not be super efficient, but
sometimes that is really your only option. Verticals don't
have to be elevated either, although if you can elevate one
you might be better off. And it doesn't have to be elevated
nearly as much as a dipole--just enough to start chipping
away at the ground loss issue. I think the "rule of thumb"
is to elevate it at least 1/10 wavelength to start getting
some real benefit.
Vertical antennas tend to have lower take-off
angles--particularly compared to a dipole at a relatively
low height. So, you might work stations closer to you
better with the dipole, but stations farther away may hear
you better on the vertical. For certain you need some
radials, but they don't necessarily have to be all that
long. As we have been told by those more knowledgeable,
more shorter radials are often better than just a few longer
ones.
Vertical systems like the MP-1 and PAC-12 are darn good
little systems. Admittedly, they could be better, but you
can also make them better. You can add more length below
and above the coil for starters. Also, you can spread more
radials than are supplied. But even as supplied, these
systems do work, and work fairly well. I've used both
systems enough times to attest to that. Furthermore, I can
use these systems in lots of situations where a dipole just
isn't possible. It's not that I prefer using
verticals--actually when I can I put up a multiband dipole
system--but it all depends on circumstances as to which type
of antenna works better.
I would conclude my comments by posing a hypothetical
situation to you. I'm not sure I know the answer, but I
think I do. Let's assume you want to work some "DX" on 40
meters from your campsite. You are in a situation where you
could put up a dipole at 30 feet, maybe even 35 feet.
Alternatively, you could use a limb, or something like that,
to elevate an MP-1 (enhanced maybe with an extra rod or two
under the coil, and maybe one or two more on top as well)
about 20 feet with 4 tuned radials sloping downward. Which
antenna has the smaller "footprint" with regard to your
campsite? Which one is apt to perform better at working DX?
Is one substantially harder than the other to put up?
Anybody want to play the game? Sorry, no prizes for the
"correct" answers since I can't say for certain what they
are!
Dave W7AQK
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, March 03, 2008 4:49 AM
Subject: [Elecraft] Re: Portable Antennae
Ken wrote:
...I would like to construct a good portable antennae to
use while camping
Mike responded:
...I have played around with multi-band HF antennas for
camping and backpacking
for more than 30 years. I've tried resonant dipoles with
and without traps,
untuned dipoles fed with balanced line, simple and complex
verticals, fed-fed
wires, etc.
I have never found anything that works as well as the
least-expensive of the
above...the resonant dipole. I have never found anything
that works as poorly
as verticals....."
......................
Ken, I would agree with Mike! I built this very antenna in a
short time after Mike sent me a simple diagram/link. I built
the antenna probably four or five years ago and still use
it. I used it immediately after Hurricane Katrina with my K1
and solar panel set up for nearly two weeks after the storm.
I just use a light weight painters pole and bugie cord it to
a suitable, but stationary anchor. As Mike said, it's easily
adjustable and it works great given it's simpicity.
Thanks Mike for sending those plans several years ago! And
Ken, I'd try it. You'll be surprised!
73,
John-KD5EJA
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