"W5DXP" wrote in message
...
On Wednesday, June 20, 2012 11:38:42 PM UTC-5, Irv Finkleman wrote:

(snipped here and there for brevity!)

----- Original Message -----
From: "W5DXP"
Newsgroups: rec.radio.amateur.antenna
Sent: Thursday, June 21, 2012 9:45 AM
Subject: Cecil et al -- Using A Lecher Line with a G5RV



Please explain further. Lecher wires usually require a short between the two
wires and we don't want that. What we need is a way to stretch or shrink the
length of the wires, a pair of conductive bungee cords perhaps?

I envisioned a pair of reasonably close spaced conductors (like open wire
line) and no short -- in other words it would
be used with a sliding tap on each side to control the length -- thus
simulating a variable length for the 300 ohm feeder.

1. How much radiation would I find in proximity to the
lecher feeder and 300 ohm twin lead. Purely a health
consideration.

Unless the power levels are very high, IMO, a tempest in a teapot. I
remember when 11m diathermy machines were all the rage. Balanced
transmission line fields tend to cancel a few inches from the wires. I
wouldn't grab them - just keep your body organs a foot or so away. I doubt
that the RF fields can hurt your hands but that's just my opinion. I've been
around RF for 60 years with no ill effects that I am aware of. Of course, RF
exposure could be the cause of me being unaware.


2. How much variation in length could I get away
with if I wanted to use a shorter lecher system, or would
I get significant i.e. noticeable benefit by going to the optimum length
for each band?

I still don't understand exactly what you have in mind. If you move taps up
and down a Lecher line, you will be leaving an *open circuit stub* attached
which will introduce capacitance into the configuration. That capacitance
will change the impedance to other than the expected value making it hard to
locate a purely resistive current maximum point.

What I mean is, for example, say the optimum length for the feedline on 80M
is 32 ft, on 40M 34 ft. and on 20M 33 ft. If I were to
use the average 33 ft. and operate only on those three bands would I notice
any significant difference -- would it make much difference
in my signal at the receiving operators shack? 99.9% of my operations over
the years have been on those three bands, and if
I didn't have to adjust the feedline length I could save a lot of time and
trouble. When I had my house, and was in fitter condition,
I could afford the effort to experiment, but now I am somewhat disabled and
what was once fun (the experimenting) is now pretty
much out of the question.

3. How far from your operating position is your
feedline/switching arrangement? Have you noticed
any hair loss since implimenting the system?

I've lost some hair but I am not nearly as bald as my father who was not
a ham. My switches were mounted on a piece of plexiglass in a window within
reach of my operating position. The switches were on the inside and the
loops of ladder-line were on the outside. There's a picture of the
plexiglass panel on my web page.

Within reach of the operating position makes the switching arrangement quite
viable, especially running QRP. Maybe I'll go that
way -- even a 10 ft or 11 ft lecher wire (unshorted, of course) would be far
more awkward.

I could set up a G5RV if I fudge a bit

I was once working on a magazine article describing a relay switched
all-HF-band G5RV. Someone else said he had submitted such an article for
publication so I stopped working on it. I don't remember who it was and have
never seen such an article. If one forgoes 30m, the parallel section only
needs to be switched between 28' and 38'. I guess I should go back and
complete that magazine article. I could envision 10' of copper rod slipping
in and out of 10' of copper tubing and controlled from the operating
position, something like a screwdriver mobile antenna.

I've never seen an article of the sort myself, and I spent a lot of time
perusing antenna articles in the various
ham radio magazines. If I had, I'm pretty sure I'd remember it, even with
my increasing 'senior memory moments'!

Thanks for your reply Cecil -- as soon as I press the 'SEND' button I'll be
off to your site where I've been many times.

73

Irv VE6BP