Hi Cecil,

I've moved off the loop and noise suppression thread and over here because
I'd like to consider an idea, and get yours and other opinions on the matter
of adjusting the 300 ohm feeder length on the G5RV.

On your G5RV page http://www.w5dxp.com/G5RV.HTM
you state that if some method is devised to vary the length of the
300 ohm series matching section it could be made to work well
on all bands.

I was wondering about using a Lecher Wire Feeder in the
shack. It would be fed from the rig by some 50 ohm
coax, and then used as the beginning of the300 line feeder, the
remainder would run out the window and up to the antenna.
..
This would allow quick and easy of adjustment of optimum
length for each band. For me, using 34 feet on 40M, and
23 feet on 10M, an 11 or 12 foot lecher setup would do
the trick.

I have seen your switched twin-lead arrangement and it
is still under consideration.

A couple of questions (which may give rise to more....)

1. How much radiation would I find in proximity to the
lecher feeder and 300 ohm twin lead. Purely a health
consideration It will not affect me as

(1) I have worked
around a lot of RF in my times -- as a tech at navy
broadcast trasmitting sites, on Heavy Radars (Pinetree
Line stuff), on shipboard trasmitting equipment, and
50 plus years of ham radio: and
(2) I only run 5W maximum
(if I'm lucky -- FT-817ND), and
(3) I've already lost most of my hair, and
(4) According to family opinion I lost it all (and I'm
not talking hair) manyyears ago and am easily
certifiable now!

Is there a cure for Ham Radio RF overexposure?

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 only operate non-WARC. I would happy
restrict myself to the 80, 40 and 20M bands, and could
drop 40 if the economics and physical reality make it
worthwhile in terms of complexity and cost vs output.

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

I am currently in a situation where an all-band dipole
is out of the question physically, and I think that if it turns
out worthwhile, I could set up a G5RV if I fudge a bit
by bending the legs a bit here and there, I don't
care about pattern, I just want to get a signal out
where someone will hear it (hopefully).

I would have looked up Smith Chart except that
I didn't even know how to spell Smith!

Thank you Cecil and any others who care to contribute
toward this thread

Irv VE6BP

On Wednesday, June 20, 2012 11:38:42 PM UTC-5, Irv Finkleman wrote:
I was wondering about using a Lecher Wire Feeder in the
shack.
This would allow quick and easy of adjustment of optimum
length for each band.

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 have seen your switched twin-lead arrangement and it
is still under consideration.

I've tried other configurations like parallel mobile telescoping antennas and copper rods that slip in and out of copper tubing. The switches take no more time than adjusting a tuner and could be automated with a microcomputer and relays.

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.

Is there a cure for Ham Radio RF overexposure?

It is non-ionizing radiation so most of what to worry about is burning. I'm sure you have burned RF holes in your fingers before. I once burned a hole in my lip from a "hot" metal microphone - still have the scar. I wasn't using a balun on a coax-fed dipole.

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.

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.

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.
--
73, Cecil, w5dxp.com

"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

On Thursday, June 21, 2012 11:35:29 AM UTC-5, Irv Finkleman wrote:
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.

As I explained in my last posting, that won't work as expected because it leaves an open-circuit stub in the circuit. I previously tried just shorting out a loop to decrease the length. It didn't work because it created a reactive stub.

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?

My 20m rotatable dipole works that way with the internal autotuner on my IC-756PRO. With ~70' of 300 ohm ladder-line, the tuner will find a match on 20m, 17m, 12m, and 10m. I was never lucky enough to achieve a satisfactory SWR on more than two bands without a tuner. However, there are certain combinations of dipole length and feedline that work on multiple bands. The ZS6BKW antenna with a dipole length of 90' and a ladder-line length of 40' is said to work without a tuner on 5 HF bands if one is lucky.

Here's a DOS-based program that I wrote that locates the current maximum points on a transmission line. It runs under XP but DOSBox is needed for later versions of Windows.

http://www.w5dxp.com/IMAXGRAF.EXE

The accompanying article is:

http://www.w5dxp.com/goodbad.htm

P.S. Two weeks ago at a neighbor boy's birthday party, I spent about three hours in the hot Texas sun playing on a large water slide and I am still paying for it. But if I die, I'll die happy.
--
73, Cecil, w5dxp.com