On Aug 27, 10:38 am, "John Doe" wrote:

My idea is to strap either a metal or pvc painted pole near the top of the
tree, with a mount bracket for the whip (of course all painted to look like
the tree). I will have to feed it with RG-8x (painted) run down the tree and
buried in a trench to the house.

As far as radials go - They are out of the question. Instead - what do you
think if I should just roll up say 250ft of 13ga or so of single conductor
wire about a foot in diameter, attached at the base of the mounting bracket
(hung in the tree) and use it as a counterpoise? I might be able to hang in
the lower branches of the tree - a waterproof box with a loading coil and
attach the counterpoise there instead?

Well, I suppose anything would be better than nothing, but you are
going to be very limited with this setup. The rules of thumb here
are make the radiating part of your antenna as long as possible to
increase the radiation resistance, make the tuning elements as
efficient as possible to avoid losses due to circulating currents.
For verticals, radials allow higher efficiency and although you may be
able to bring the antenna into resonance at the desired operating
frequency without them, your radiated signal will usually benefit from
as many of them as you can manage. Any radials will help, but just
one that is coiled at the bottom of the vertical is not going to make
up for all the compromises you are making with this design. 40 feet
will make a pretty good vertical perhaps down to the 30 Meters but as
you get on 40 meters and below it's getting pretty short.

On the low frequency bands, your vertical will have very narrow
bandwidth are horrid radiation efficiency as you describe it. It may
very well be usable for you, but there may be other options that will
be more effective on the lower frequency bands (40, 80, 160 Meters).

Have you considered transmitting loops for the lower frequency bands?
They have the advantage of being directional which can help you on
both transmit and receive. Their efficiency is pretty bad, but when
matched against a vertical configured as yours, I'd bet they would be
as good or better in most respects. You will likely be power limited
with these antennas, but properly designed and tuned they can work
quite well. Keep the resistance of your loop and the losses in the
matching network as low as possible and you may discover that they are
better solutions for you.

Usually transmitting loops (or magnetic loops as they are sometimes
called) are home grown affairs. I know of a few products available
for this.. I believe that MFJ has some loop tuner products, and Bail
Isotron makes some things that look like loops to me for various low
frequency bands. (These Isotron antennas have very mixed reviews and I
would figure that they work fairly well when tuned correctly, but they
are difficult to tune properly.) Usually the two biggest issues
facing loops is the voltages and currents produced with very low
transmit powers can be very large and finding the matching components
that can handle the currents and voltages while not introducing IR
losses. Making low resistance loops is not that hard, but finding
variable capacitors that can handle the current and voltages produced
in a single turn loop with even 100 Watts can be difficult (and
expensive.) Going for more than 100 watts is possible, but will
almost assure you of having to home grow just about the whole thing.

Loop antennas also present some unique operating challenges as their
operating bandwidth is VERY limited (approaching SSB Bandwidths at
times) so any frequency changes will include a lengthy period of time
to re-tune and because they are usually located very close to the
operator they can be an RF exposure risk. However, if properly built
they are easy to rotate and provide some directional gain which can be
a HUGE benefit over your standard vertical. You may be putting less
power out of the loop, but it is concentrated in some directions so
your effective power towards the intended location can be much higher.

My advice is to concentrate on your 40 foot tree for 30 meters and up
and for 40 meters on down look to other options. The vertical just
isn't going to perform well as you get down to the lower frequency
bands. I'd also pretty much forget 160 meters unless you will be
happy with a very small bandwidth and very poor performance on either
loops or your current vertical idea.

By the way, I am interested in the Isotron antennas because I live in
a very limiting CC&R environment and I have pretty much zero in the
way of trees to hide antennas in. I'm pretty much limited to what I
can hide in my attic. My trap dipole is pretty much junk on anything
over longer than 30 meters, but what can I expect considering that
it's only about 20 feet up, surrounded by the whole house's worth of
electrical wire and furnace ducting while pretty much limited to about
60 feet long. Oh to get the sunspots back soon!

-= Bob =-