Jim,
My home QTH and all my DXpeditions had SpiderPole
verticals for 80 and 160 (and other bands). You have a
wide range of options. A lot depends on how much work you
are willing to do and how much efficiency you want to
squeeze out of the system.
The simplest arrangement would be a low loss loading coil
(around 60 uH) somewhere in the middle to resonate the
antenna on 1.9 MHz. Use AWG #14 insulated wire for the
whole length and fold it back at the tip to create a 30 cm
(1 foot) diameter loop to reduce voltages on the tip and
to add a little bit of top loading. Add an approximately 8
uH inductor between the base and GND. You will find a 50
ohm tap point on the inductor somewhere around the center.
For the base inductor use 1/4 inch copper pipe or large
diameter wire. For 80 m use a relay to switch in a
suitable L matching network.
An alternative is to use an inverted L configuration. Use
very thin wire for the horizontal section to reduce the
side load as the tope part of the SpiderPole is very
flexible. You may find that you can get decent SWR with
the 50 ohm coax connected directly to the feed-point.
(That would indicate a high ground system impedance and
substantial losses, but...) Otherwise use a simple L
network to match the coax to the feed-point. One word of
caution, an inverted L that is resonant on 160 will have a
very high reactive feed-point impedance on 80 and will
also have a high radiation angle. You can use a shorter
horizontal wire (around 8 meters) and two switchable
matching networks, one for 80 and one for 160 m. An
alternative to consider is to leave off the top two
sections of the 26 m SpiderPole to create a stiffer pole
which can hold more side load. The horizontal wire would
have to be correspondingly longer but the improvement in
mechanical strength would be well worth the slightly lower
efficiency.
For something a lot more elaborate (and something that can
cover all bands, check out the antenna used on VK9GMW.
(http://vk9gmw.com/documents/VK9GMW_ANTENNA.pdf ) That
antenna worked great because of the salt water, but with
enough radials you could get good performance on land too.
For a permanent installation I strongly recommend that you
paint the antenna once you got it working. Use flexible
urethane paint. It will make it last 5 times longer. You
should also have at least 3 guy ropes, attached somewhere
around the middle. For ultimate strength, buy two poles
and insert one inside the other. The antenna at my QTH has
an 11 m tall 100 mm diameter aluminum tube with two 18 m
SpiderPoles on top, for a total height of 29 m. No guy
ropes. It works from 160 to 30 m via a tuner and has been
up since 2009. (You can see a picture of this antenna on
my QRZ.com page.)
GL and 73,
George,
AA7JV
On Fri, 23 Aug 2013 10:46:43 -0600
"Jim Garland" <4cx250b@miamioh.edu> wrote:
Hi everyone,
I'm _finally_ trying to erect a decent vertical for 80m
and 160m, and have
purchased a 26m (85ft) Spiderbeam mast. I'd really like
to hear from guys
who have used this mast for these bands. I'll have about
60 120ft radials.
I've seen sheet from the manufacturer about using the
mast as a monoband
160m shortened vertical. The diagram shows a wire wound
aound the mast, with
4 7m wires near the top for a capacity hat, but wonder
what other
configurations people have used? Also, if possible I'd
like to be able to
use the mast on both 80m and 160m. It will located about
600 ft from my
house.
73,
Jim W8ZR
_________________
Topband Reflector
_________________
Topband Reflector
|