On Sat, 5 Oct 2013 13:27:43 -0600, "Irv Finkleman"
wrote:

To begin with I run QRP (5W on a Yaesu ft-817ND).

In that case, almost any coil form will work. There's little danger
from losses causing the plastic to melt. However, I'm not so thrilled
with the idea of using wood. The wood is not the problem. It's the
water in the wood. You can seal it with the traditional bees wax, but
that tends to become a sticky mess.

I'm considering a homebrew loaded whip, as it would be quick and simple.

Nothing is both quick and simple. The simple things take forever to
get right and the quick things that are thrown together never seem to
work.

Later on I hope to build a magnetic loop.

That's the best idea yet. They're very narrow band, kinda
temperamental, require plenty of expensive copper, good soldering,
giant air dielectric or vacuum capacitors, but work better than
anything their size.

However, if you must waste your time with a base loaded whip, your
first problem will be finding a suitable ground. That's a problem you
don't have with a dipole or loop. I guess some welded wire mesh on
the balcony will barely suffice. Next, you need a base insulator. I
recommend an empty thick glass wine bottle. Wrap some stiff insulated
wire around the bottle as a loading coil. Use your MFJ259 to tune to
the right band. Make an assortment of wine bottle loading coils, one
for each band.

I only run QRP on a Yaesu
FT-817ND. I also have at my disposal an artificial ground tuner, an
MFJ-949E Antenna Tuner, an MFJ-259B Analyzer, a MFJ-1625
Window/Balcony Mount Antenna system, and a MFJ-931 Artificial
Ground. The Windowsill/Balcony tuner also has an Artificial Ground
Tuner in it too.

Tuners are fun to play with but are often lossy. If you get the
loading coil close to 50 ohms at the operating frequency, you can live
without the tuner. At worst, use the tuner for minor VSWR adjustments
when you change frequency, and don't want to play with the loading
coil.

The 259B I bought new
in the box!

For when you blow it up:
http://802.11junk.com/jeffl/MFJ-269-repair/
That's for an MFJ269, which is similar.

I'm not overly concerned about
Q as long as I can get a signal out!

Besides bandwidth, Q is also way to express losses. Basically, it's a
measure of either the series resistance or parallel resistance of an
ideal inductor.

For parallel:
Rp = Xl * Q
Rp = 2 * Pi * freq * L * Q

For Series:
Rs = Xc / Q
Rs = 1 / (2 * Pi * freq * Q)
(Note that Rs is also known as the capacitor ESR).

A high Q coil has a large resistor across it with minimal effects,
while a low Q coil will have a much smaller resistor across it. Since
pure reactances do NOT dissipate any power, all the power loss in the
coil is dissipated in this equivalent resistance. There's also the DC
resistance of the coil in series but that's not part of the current
discussion.

My main concern was with winding a loading coil on
a square form, and I was just wondering how much
effect that would have.

Obviously, it produces square waves.

The shape of the form will have almost no effect on the inductance, Q,
or radiation characteristics of the antenna. If you look carefully at
the cross section of a torroid core, you'll find that it's wound in a
square pattern.

I've
undergone three major surgeries since late 2009 and
had to sell my house.

Ouch. Get better please.

I gave all my ham stuff to the
local radio club thinking then that I'd never be able to
ham again -- now I'm starting again! I've had my
ticket for 55 years and it's not easy to stop!!!

No sympathy. I've moved about 4 times. Each time, I purged my ham
radio, magazine, auto parts, and junk collections in the anticipation
of never needing them again. Each time, I quickly rebuilt the mess. I
don't plan to move, but the mess has once again reached the safe
occupancy level and needs to be purged. Sigh...

After this discussion I think I'll go ABS, and with
the aid of some epoxy may even slip it off the
pipe and go air core supporting the coil off to the
side of the whip mounting. Remember the old
'Gotham Vertical' antennas (1956 Handbook ads)?

Ok. Just use the white ABS pipe, not the black ABS irrigation pipe.

In any event, what do you think of the homebrew
equivalent of AirDux, but square instead of round?

No problem. It should work the same as the round flavor.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558