On Thu, 15 Nov 2007 11:49:54 -0800, Andreas Hofmann wrote:
>Thanks for all the responses I have received. Great group of knowledgeable
people. Yes I do have the books most of you suggested...
>A couple of follow up questions:
>1. The wire should be insulated since it will touch branches/trunk, right?
Yes. If it's close enough to touch at the ends, it will arc with high power (I
have the charred pieces of wire to prove it). If it's close near the center,
there
can be some loss due to the resistive absorption already discussed.
>2. Radials seem to be the most important thing. Do they have to be a certain
length wires
On the ground, length is not critical, except that longer and more are better,
and
more close to the antenna is more important than long.
or can I use something like wire mesh sold reinforcing concrete patios?
If it will hold up and not rot, yes.
>3. I know any structures should be as far as away as possible, but how far.
Would my house in say 25 m distance (75 feet) be a major problem? Even if the
direction of the house is not a major desired radiation direction?
Don't worry about it. The conductive parts may affect things a bit, but your
antenna will work.
>4. Safety. How do people protect the antenna/radials from being touched by
kids/animals etc.?
Insulation.
>5. Can I get away with not having radials if it is a vertical dipole feed in
>the
middle
YES.
>6. I am reading that a quarter wave vertical has about 31 Ohm of impedance.
>How
does it get matched to 50 Ohm coax?
First, the loss in the ground system will add some R to that. You can use a
matching network, or let your antenna tuner deal with the mismatch that
remains.
Again, don't worry about it unless it's a really long run of small coax, in
which
case it's a good time to pop for some big coax.
73,
Jim K9YC
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