Thanks John,

Taking the cost of copper into account (Unless I can find one of those
old power transformers and strip it) I'll just wind 'lots' of turns -- maybe
about 50% more than shown in the QST Articles on windowsill antennas.
It's easy to short the extra turns if I don't need them.

As for Jeff's reply -- he has always been helpful to the max, and some of
it is my fault in that I am basically tossing ideas into the air and
sparking
discussion as part of my preliminary design considerations. The army
guys I know (I was diehard Navy) had an expression 'Time spent on
recconaissance is seldom wasted" and I tend to work that way which
is sort of 'Measure twice, cut once' taking into account Murphy's Laws.

It may take me longer to get on the air, but once there, I plan to have
a lot of fun!

Thanks again all!

Irv VE6BP


"John S" wrote in message
...
On 10/5/2013 11:11 AM, Jeff Liebermann wrote:
On Fri, 4 Oct 2013 21:48:30 -0600, "Irv Finkleman"
wrote:

I wonder how much difference it would make if I were to
build a loading coil on a piece of 3''x3" wood?

Difference from what? What are you comparing the wood coil with?

Good question.

It would be
very easy and I could suspend the winding above the wood
form with plastic dowel glued on each corner of the wood.
I could also make a similar coil using PVC pipe. Even in that
case the winding would have a somewhat rectangular form
factor.

Yep. Both PCV and wood are lossy. Put a piece in your microwave oven
and watch them both get warm. Actually, if the wood has a high
moisture content, it will get quite hot. If exposed, both materials
also have problems with UV resistance. If you must use plastic
tubing, you can possibly find something in polysulfone, polystyrene,
polypropylene, or polycarbonate (in order of preference). If you
can't find these, white ABS schedule 40 sorta works at low power
levels.

The microwave oven test is not very useful. The microwave will test
whatever at about 2450MHz. I doubt he is trying to make a loading coil for
anything near that frequency.

There are other resources for that information. Please search.

High power or low power? If low power, you could probably wind the
loading coal on kiln dried and sealed wood or PVC and it will work. On
the other foot, high power will heat anything that's lossy, including
the coil form.

You are correct. But, the losses (percentage-wise) will be the same
barring heating effects.

High Q or low Q? If you need a really high Q loading coil, the
material losses might be a problem.

See above.

It wouldn't be air core considering that it would be over
wood (dry and waterproofed) or PVC pipe.

Try this, Jeff...

Wind some turns on an empty plastic soft drink bottle. Measure the L and Q
and SRF. Then fill it with water. Measure the L and Q and SRF again.
Report back here with the data.

I do require the structure be relatively strong or I
would wind the coil, put epoxy glue strips along it
to make it like AirDux and the like.

Irv... You might need a few more turns to get the L you need, but it is
hard to read your practical limitations from this. If that is all you
have, give it a try. What do you have to lose? Do you have a way of
measuring the L?

Strong, relative to what? Are you supporting a tower on the coil, or
a length of wire? Some clues as to the weight load, and other
stresses (torque, shear, vibration, etc) would be helpful.

If you have read his previous posts, you would know that he is in an
apartment and has a balcony. He wishes to operate from that location.

Correct me if I am wrong, Irv.

Any comments or suggestions??

Nope. You haven't stated what you're trying to accomplish or what you
have to work with.

Most posters here do not state all of the facts initially. That's because
most of their ideas are still brewing in the brain and some of the details
are not formalized. It is the reason we ask for other people's inputs. Cut
him some slack and continue to ask how you can help.

Wishing you the best, Irv.

Cheers and 73,
John KD5YI