I In a message dated 7/20/01 2:29:02 PM Pacific Daylight Time,
charlie.ocker@tellabs.com writes:
<<
Bill Coleman wrote:
> How about mounting a balun outside, and bringing coax underground / into
> the building?
A balun work's best when it see's a pure resistance, or nearly so. A
balun at the end of a piece of coax, feeding a length of balanced line
that feeds an antenna, will almost be guaranteed to see a reactive load.
A better idea would be to place the balun at the input of a balanced
tuner. If there are difficulties in bringing in the balanced line to
the tuner, then a small section of shielded balanced line can be
employed.
73, Charlie N9CO (no expert on balanced lines, just my empirical
observations)
>>
A random coax length and a short open wire line here adds up to a length
that can often increase (but not always) the reactive component on each
band.
As I suggested a balanced 100 or 150 ohm coax "Needs No Balun", matches the
loop fairly close on the various bands, is very tolerant to SWRs above 2:1
on
160,80&40M, presents low reactive Z's to the tuner with a loop cut for say
1.78 MHz on all band and a coax that is multiple of 91' 2" of .66 VF. It
matches easily and quickly with the 2 knobs of a Match Box also modified for
160M. I've been there and done that off an on now for about 50 years to be
fairly firm on my recommendation for the least problems.
I've had tuners at the antenna controlled with 2 selsyns and a stepping band
switch but on the LF's, it's a "total waste of time 2 ways and a serious
elevated housing problem". Open wire line (of certain lengths) is so
forgivig with the proper tuner in the shack and knowledge how to use it,
this
system is very practical indeed. 6M an up tuners and amplifiers at the
antenna is a good idea. Keep it simple.
If you can use open wire line the losses are even less and far cheaper than
coax. One TTer has a full size 80M vertical 500' or more way fed with open
wire line, 2 low loss baluns, had a measured loss less than a dB as I
remember, it doesn't change and is easy to repair if needed. I don't think
the coax exists with that low loss at any cost for that length. Use
multiples of 137' for .98 VF and 123' for 450 ohm ladder .89 VF line for the
friendliest Z's the tuner will ever see on all bands. ARRL keeps making the
serious mistake of recommending "open wire line of any length". That has
done more to lower the popularity of open wire line and those who have
trouble adjusting the Match Box and/or other tuners than any other factor in
Ham Radio. Running it on top of a wooden fence line is a great idea. If
you
don't have a wooden fence--put one in whether you need it or not. Feedline
Security you know. Or dress it up, use big poles and make it look like a
110V power line and it "will look natural" even to the neigbors.
The "Cloud Warmer" label for the Horizontal Quad Loops is really not
accurate in one sence. It infers the Clouds are "resistive." Actually all
RF goes through clouds and with high angle it goes through 2 horizontal
layers. With a low angle the RF goes through a long length of the Cloud
layer twice again which in miles can be much longer. If clouds are
resistive
the loss would be higher for the same thickness of them. High angle is
optimum for most contacts on the LF's other than for DX and high angle is
open 24 hours a day year around where low angle skip isn't. The RF after
using a small area under the antenna for a reflector which can be improved
with a small square radial system or chicken wire, will not touch ground
before it hits most of the receiving antenna first. It's a very low loss
path all the way. I call it the "Slam Dunk Antenna." It often does better
than a dipole the same height for certain reasons that aren't entirely
obvious other than it's actually a 2 element beam with a quad DE already
with
2 dB gain with a higher feedpoint Z. It reaches out very well also. The
75M
loop I had 20' high with no radial system under it in SD fed with 137' of
open wire line would give a 20/9 report with 100W into Seattle no dipole
would. This performance was hard to explain and I didn't really care--it
flat out worked great. It worked great on 160M also.
The only antenna I had in SD prior to '56 that worked on a par on 75M was a
top loaded 75M dipole 60' high with the feeders tied together. W7IIP then
W8IIP was the first I heard using it from Bremerton,Wa and he had a great
signal 3-6 S units above its strength used as a horizontal as was similar
with my horizontal. I'm anxious to add a ground system under horizontal
loops to see what it does for the signal at all distances and will have the
chance to do this for a show down side by side--one with and one without.
Enjoy the mystery, use one and tell your own signal success stories. If you
want DX put up a 4 Square or a "vertical in the middle of the loop," play
the
various phasing games and share a dual radial system--it's been done before
and it works. How about a horizontal loop suspended inbetween the tips of a
4 square? It's worth a try in Eznec first. To reduce coupling to the 4
Square tips whatever it might be, one could install the loop for the next
highr band. There is a way to load a quad loop at 1/2 F and it will still
have great performance with a similar broadside pattern. Be creative! K7GCO
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