Hi Jeff, and thanks for your reply.
To begin with I run QRP (5W on a Yaesu ft-817ND).
I have limited workshop space (my desk in a senior's villa), but
lots of my old tools.
I ran into problems in the last senior's residence I lived in and have just
now moved into a new one. All my previous preparations to set up an
antenna have been foiled -- one old busybody saw us stringing a line
out of my window to a nearby tree. Before anything could be done she
had a whole bunch crying to the General Manager that we were (a) killing
trees (b) setting up satellite antennas on the roof (c) going to interfere
with
radios, TVs, heating pads and such. So much attention was drawn to
a simple twenty foot piece of small nearly invisible wire that I decided it
would be easier to move than fight a battle that I had little chance of
winning.
The unit I am in now has a balcony, and I have moved in with the
understanding that I will not have any wires hanging off the balcony
to nearby trees etc., and that anything I do set up will remain within
the confines of the small balcony (roughly 6ft x 10ft. They do not
mind if I have a collapsible whip or somnething similar which could
be taken in (or out ofsight) when I'm not operating -- they don't
want it left sticking out.
I'm considering a homebrew loaded whip, as it would be quick and simple.
Later on I hope to build a magnetic loop. 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.
The loading coil with the MFJ-1625 is pretty flimsy and I might just
consider rewinding the coil with heavier copper (the orginal coil had
a broken turn). All of the aforementioned
equipment I picked up used or broken and fixed
up (a little extra solder in the right places never
hurt MFJ stuff), the 931 had a blown meter, the
FT-817ND had a burned foil on the board due to faulty hookup or
something, and the 949 needed a switch replaced. The 259B I bought new
in the box!
I was comparing a wood coil with an air wound coil.
I should have said ABS rather than PVC, and I am
well aware of dielectric losses although I don't worry
about them too much as even 5W minus the losses will
keep me on the air. I'm not overly concerned about
Q as long as I can get a signal out!
My main concern was with winding a loading coil on
a square form, and I was just wondering how much
effect that would have.
Coincidentally, today was our local Ham Flea Market,
but I am somewhat handicapped and was not up to
going -- normally I would crawl across broken glass
to attend. I might have found something there. I've
undergone three major surgeries since late 2009 and
had to sell my house. 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!!!
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)?
All of this is planning ahead -- I'll try the MFJ-1625
setup first, just to get going.
In any event, what do you think of the homebrew
equivalent of AirDux, but square instead of round?
Irv VE6BP
"Jeff Liebermann" wrote in message
...
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?
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.
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.
High Q or low Q? If you need a really high Q loading coil, the
material losses might be a problem.
Hints:
http://www.w8ji.com/loading_inductors.htm
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/HiQCoil.htm
Notice the preferred loading coil construction.
This might give you some ideas (good and bad):
https://www.google.com/search?tbm=isch&q=antenna+loading+coil
It wouldn't be air core considering that it would be over
wood (dry and waterproofed) or PVC pipe.
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.
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.
Any comments or suggestions??
Nope. You haven't stated what you're trying to accomplish or what you
have to work with.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558