I don't really understand why traps have gotten such a bad rap. Consider
that most all triband beams use traps as well as many verticals. I have
been using Spi-Ro traps for 20 years and never had a problem and I
certainly don't see any indication that I am suffering some kind of loss
as a result. I have made many comparisons between the trapped dipoles
and single band non-trapped dipoles and the only difference I see is a
reduction in usable bandwidth. The Spi-Ro traps are rated for 600 watts
making them perfect for the KPA500 powered station. Indeed - do not
rule out traps.
I also use a similar wire that to what Charlie mentions. Last order was
for 600 feet. It's great stuff.
Now I'm thinking of what would be the best "all-band" antenna for the K2
which is my secondary operating position in the living room where I can
give demos to visitors. I'm thinking of giving the 88 foot doublet fed
with 300 ohm twinlead a try.
Doug -- K0DXV
On 6/26/14, 6:30 AM, Charlie T, K3ICH wrote:
Don't rule out traps.
Also, the RF Connection and probably others, sell a nice stranded
copperweld wire that has a black polyethylene insulation. If I
remember correctly, it is 13 ga and is ideal for antennas. For all
practical purposes, it doesn't stretch, is fairly slippery and only a
little "springier" than hard drawn copper.
I use those double ferrule aluminum crimp on's that are designed for
flexible wire cable to hold everything together. I was concerned
about them holding through the poly insulation, but the following
antenna has been up for about ten years now. It consists of a double
(fan) dipole with a pair of 80 meter traps in the top leg for 160 & 80
M coverage and a pair of 40 meter traps in the lower leg for 60 & 40 M
coverage. It is fed thru a 1:1 balun with RG-213 and is tuned for
resonance. Basically, I operate SSB 99% of the time, so the antenna
is tuned for that end of the bands. An MN-2700 tuner in the shack
takes care of small excursions from resonance. It's only up about 50
feet, so performance is what you'd expect. It's not straight either
and is sort of a lazy Z, being strung between two 55' telephone poles
that are 105 feet apart. The ends droop down at about 45 degrees to
tie-off points in trees. A compromise? Yes, but it works.
73, Charlie k3ICH
----- Original Message ----- From: "Jim Brown"
<[email protected]>
To: <[email protected]>
Sent: Thursday, June 26, 2014 1:55 AM
Subject: Re: [Elecraft] RF in the Trees
On 6/25/2014 5:43 PM, Dauer, Edward wrote:
So, I've been selecting two of the tallest
candidates a couple of hundred feet apart and stringing a stout
nylon rope
between them. In the middle of the cord I attach the balun for the
Vees,
thereby allowing the legs to be in the clear, moveable from side to
side,
and tied to smaller (8') trees at their distal ends. In one
variation on
the theme I had a 40 meter dipole as the center section of the
supporting
rope, tied to the same balun as an 80 meter vee. In another I tried a
linear-loaded 80-meter Vee, about 45' on a leg; it loaded fine but
didn't
perform as well as the full length version.
If you can suspend a flat antenna between two tall trees, why would
you want an inverted vee, which is a less effective radiator?
Your two trees 200 ft apart could support a full size 80/40 fan and a
20/15/10 fan, in line with each other. A high 80/40 fan is a VERY
good antenna, and is easy to build.
My technique has evolved to starting with #8 bare copper from the big
box store, stretch it VERY slowly between a tree and a trailer hitch
until it breaks. Do this carefully where there's no one around to get
hurt. Now you have #10 hard drawn copper, which is pretty strong, and
pre-stretched. Use that for the longest dipole in each fan. Use #12
or #14 THHN (house wire) for the other elements. I make spacers by
cutting 1/2-in PVC conduit into lengths of about 16 in for 3-wire
fans, and about 12 inches for 2-wire fans. 5-6 ft between spacers is
a good rule of thumb. Hold the spacers in place by soldering short
lengths of copper around the spacer to the bare copper of the long
element.
The higher your antenna is, the more robust your center insulator
should be. A high 80/40 dipole (80 ft or more) will be closer to 75
ohms than 50 ohms. A 20/15/10 fan will be close to 50 ohms. Use RG8
or RG11 depending on the Z at resonance. Don't waste a dB or two with
small coax. My 110 ft 80/40 fans are fed with Belden 8213.
For weights, I fill 6 gallon water jugs with dry sand, and tie one to
one end of each span. The other end can be fixed. I have pulleys high
my trees. If you don't have a pulley and weight, your antenna WILL
end up on the ground, and it won't take a big storm for that to happen.
My HF antennas are all at the 110-120 ft level in a dense redwood
forest that towers 50-75 ft above them. They work. My "seat of the
pants" observation is that attenuation increases with frequency, and
is greatest with vertical polarization. 432 MHz is a waste of time,
2M sort of works, and 6M works pretty well.
For an analysis of the value of height, study this. It supports the
statement earlier in this thread that a high dipole beats a low
tri-bander.
http://k9yc.com/VertOrHorizontal-Slides.pdf
When Fred observes that the ends of antennas are "hotter," he means
that this is voltage maxima and a current minima, so good insulation
is needed to whatever the antenna is attached. I once melted heavy
dacron rope that was tied directly to the end of said dipole (well,
twice, actually). The extra ingredient was that it was wet. Duh.
73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
