The plan is to develop a simple, relatively inexpensive, relatively
light weight and shippable/airline transportable 160 antenna kit for one
man quick deployment for modest DXpeditions or contributed for use by
resident hams in rare-ish (for 160 m) locations.The ability to make
adjustments to actual deployments to provide matching is important since
such antennas are famously variable due to soil and local obstruction
environment and there should not be a need for antenna matching
hardware, especially at the planned higher powers.
First cut electrical design:Inverted L using telescoping aluminum tubes,
two elevated radials and "hairpin" matching.
Mechanical features of a prototype that was deployed:
9 Alum tubes 6', .058" walls, 2" diameter through 1" diameter -- this
gives a 50' or 15.3 m mast (it can be pulled upright by 1 person, or
probably telescoped up also)
#14 wire ~ 28 m for top wire and 2X ~34 m radials (values after some
adjustment, not unique, some tradeoff between the top and radials)
Base - 2 thicknesses of Walmart (cheap 8X11") ¼" plastic cutting board
resting on ground with a ~ 1.5" wood cylinder bolted in the
center.SO-239 connector screwed to the board.
Guys -- 4X 3/32" dacron rope attached at 7 tube height, angled at ~ 45deg
Guys held down by sandbags (very effective and moveable)
Inv L top wire end was at ~ 2.5 m height with a support of opportunity
(e.g., a tree) ~ 25 m from base
Radials have their closest support near the base from plastic rings
looped through each of an opposite pair of the guys at ~ 6 m high and 6
m from the mast.The radials therefore go from the base to the rings at
about a 45 degree angle.(Elevating the base and everything else, by a
meter did not seem to affect the impedance.Beyond that, supports of
opportunity were used - above neck height is always nice.
This produces, with some fiddling with wire lengths, an impedance around
20 -- j20 which can be matched using a practical "hairpin" coil shunt of
inductive reactance ~ 45 ohms ( 4 microHenrys, say 5 turns 4" dia).
More details of the test case including the EZNEC example are shown on
my website.There are obviously a number of ways this design could be
modified/improved, several discussed on the website.However, the
tradeoffs with size, weight and complexity must be considered in the
light of the mission here which includes transportability and ease of
deployment.
I am looking for collaborators to contribute ideas to help improve, and
potentially, test design issues.Check out the website at
http://n6mw.ehpes.com <http://n6mw.ehpes.com/> for the Itinerant 160 m
antenna project expanded discussion toward the bottom.
The immediate target is designing and assembling a respectable 160 m
antenna that might go to KH8 on a DXpedition.
Bill, N6MW
billsstuff(at)gotsky.com
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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