Backpacking antenna question (Was: Test)
 

On Tue, 21 May 2013 13:00:02 -0700, David Ryeburn
wrote:

In article ,
"Irv Finkleman" wrote:

... I haven't seen a new post in 8 days!
...
I like it when there's lots of activity on a good discussion

OK. Here's a question for someone who likes to model things.

I'll soon (if Industry Canada gets around to processing the exam which I
passed) be VE7??? and I'd like to go backpacking with a QRP CW
transceiver. I want to use a current balun at the antenna and RG-174
feedline because I've got a pacemaker inside me (else I'd just use an
end-fed halfwave). I'd prefer to have a single antenna I can use on
multiple bands.

Suppose I built a triangular closed loop one full wave long on 40
metres, with sides about 14.5 m long (whatever it takes to be resonant
on the low end of 40). I'd stretch one 14.5 m side between high branches
of two tall conifers at my camp and the other two sides would slope
downward and toward each other, meeting maybe 1 m above ground where
they'd be connected to each other, with thin rope continuing from that
junction point on down to a stake. I'd want to use this on 40, 20, 15,
and 10, and if I went out to the back where the two down-sloping wires
were connected together and disconnected them I'd then have an open loop
which would be a little long for a half-wave on 80 and more than a
little long for three half-waves on 30. What sorts of impedances would
the poor balun be subjected to on the various bands?

I'm not that worried about the SWR on the feedline or the impedance at
the transmitter; the latter can be dealt with by using an antenna tuner.
But if the balun is subjected to a load impedance that's too high or too
reactive, maybe it won't do its job well enough and some current will
come down the outside of the coax. My pacemaker might not like that.

There was a story on the TV news tonight. Ipads have small magnets in
them. If you go to sleep with your Ipad resting on your chest, the
magnets have been knows to interfere with pacemakers.

Antennas, tho', I dunno...

bob
k5qwg



David, ex-W8EZE 45 years ago and soon to be a VE7