I have to agree with Lyn on several points. I do agree the directional
pattern is different on every band. For me, that suffices as I am not
one to aggressively chase DX. If you need specific directional
patterns, then other considerations for antennas should be undertaken.
On point #2, the balanced feed line is twisted at my installation. This
is one advantage to the vinyl covered line. This makes essentially a
twisted pair which Bell Labs many years show is a way to minimize
induction into the feed line. In transforming from balanced to
unbalanced, I use two "baluns" at the shack end of the feed line. One
is a 4:1 dual core balun operating as a wide band transformer and the
second is a 1:1 balun operating as a balanced to unbalanced
configuration. It also provides a significant amount of common mode
current rejection. This has been verified by measurement of the common
mode current on the shield of the short jumper between the balun and the
ATU. {See https://www.dj0ip.de/balun-stuff/ }
As to the research N7WS, I've read his paper several times. In fact,
a fresh copy is on my desk. Due to test equipment limitations, he did
his wet/dry line measurements at 50 MHz and higher with a short piece of
feed line. I did my measurements between 1.8 MHz and 30 MHz with 100
ft of feed line. The line was measured, for wet/dry purposes, in a
matched impedance configuration between 1.8 MHz and 30 MHz. I agree
with his data on velocity factor changes but can not agree on increased
loss data.
The work of KV5R where he references; "Many amateurs use non-resonant
(even random length) antennas fed with open wire lines and tuners. They
radiate signals just as well as those fed with coaxial cable and
resonant antennas. ...... ARRL Antenna Book, Ch2" As long as the
antenna length is 1/2 wavelength at the lowest frequency the efficiency
is near 90%. {See KV5R.Com}
The work of G3TXQ seems to contradict parts of the work done by N7WS.
His measurement for wet/dry line being 60ft of 300 ohm line
configuration with a 6:1 SWR does more agree with my measurements using
100 ft of line. Thus 60 ft of dry line at 27.0 MHz shows 0.71 dB loss
and 0.93 dB loss when wet. His measurements of 450 ohm window line
fall within the same range of loss measurements between wet or dry.
As to noise in the local area at my QTH, having two different antennas,
one being a resonant dipole fed with a 1:1 current balun at the feed
point and RG-213 and the other being a 256 ft center fed wire with a
balanced feed I do not find the balanced fed antenna to be any more
prone to noise than the resonant dipole on 80M and 20M. There is a
bit of a skew in orientation due to placement of the ends.
A 2nd test, at a 2nd site which easily allows one antenna to be pulled
in place and measured and then lowered and the a 2nd antenna pulled into
the same location, I find again there is no difference between a coax
fed antenna and one fed with balanced feed line, in terms of noise
pickup. Field strength measurements at several points at a distance of
approximately 1 mile is indeterminable between the two.
As the song says "that's my story and I'm sticking to it".
73
Bob,K4TAX
On 3/18/2020 7:39 AM, Lyn Norstad wrote:
Jim -
Your comments are well taken ... but mostly invalid for my installation.
For example -
1) Their directional patterns are different on every band;
Exactly, and this plays perfectly into my coverage needs. For example, I
need (and designed for) 80 meter coverage concentrated in a N-S direction.
For every other band, I need (and designed for) more of an omni pattern.
That works best for me and is reasonably well provided by this antenna's
multi-lobe patterns.
2) They have very poor rejection of common mode noise on the feedline
unless choked at the FEEDPOINT (i.e. where the feedline connects to the
horizontal wires) and I know of no practical choke to do that effectively.
I have a hybrid 4:1 / 1:1 balun at the shack end of the balanced feedline
and have absolutely no issues. None. It is a Balun Designs 4116t.
5) Many years ago, N7WS published his research showing that window
line gets pretty lossy when wet. It's in one of ARRL's excellent Antenna
Compendiums.
Agreed, and that's why I didn't use window line. I used open-wire, or true
ladder line, from TrueLadderLine.com. Rain has no effect unless the line
itself is pressed against tree leaves (I do have to do a little tree
trimming now and then).
Noise level is markedly lower than reported by other hams in the area,
whether using vertical or compromised horizontal antennas. My noise level
went down at least 2-3 S units in switching from the attic-mounted G5RV Jr,
while both received and transmitted signals are higher by a similar amount.
Bottom line is that it does what it is intended to do, and does it quite
well.
73
Lyn, W0LEN
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