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The W3DZZ Antenna

Posted: 06 Jan 2016 02:58 PM PST
http://www.iw5edi.com/ham-radio/2032/w3dzz-antenna

W3DZZ Antenna


Moonraker supply a whole range of wire trap dipoles covering from 2 to 5 HF
bands (MTD1; MTD2; MTD3; MTD4; MTD5; MTD6). Diamond also produce trapped
wire antennas, the W-721, W-728 and W735. Comet and Diamond each produce
similar interesting 5 band wire dipoles that utilize both traps and a fan
arrangement the Diamond W8010 and the Comet CWA-1000. If space really is
limited then look out for KZJ Communications (dongo1950 on ebay) he
produces Limited Space Inductive Dipoles. These are inductively loaded and
shortened dipoles so they will have reduced efficiency, of course, but are
very nicely made, so might be very useful in a tight spot.
To obtain good efficiency and achieve a low angle of radiation, desirable
for longer distance DX, a horizontal dipole needs to be installed at a good
height over 20 feet would be desirable and it is quite common to install
horizontal dipoles at around 30 to 40 feet above ground level. This might
be a problem at some QTHs, it certainly is at mine!
Allan Copland, GM1SXX comments: The dipole will operate well on the band it
has been sized for , if placed at a suitable height, but will also operate
as a’ three-half-wave’ aerial at three times the frequency and so on, so
it’s not strictly a single band aerial.Â* An 80M dipole (132 feet typical)
will work nicely on 30 metresÂ* (three half waves) but not on 40m (two half
waves)… because on 40M the feed-pointÂ* is at a voltage node and not at a
current node, for easy feeding.Â* Most aerials are current fed.
The radiation pattern changes when a dipole is not used on its design
frequency. The pattern will break up into multiple ‘petals’. This can be
either a disadvantage or an advantage depending on what you expect from
it.Â* Since most of us use co-ax, an UN-BALÂ* should really be used to
connect the unbalanced feeder to the balanced aerial, but how many people
actually bother? Not many I suspect.Â* It’s possible of course to use a
balanced feed-lineÂ* system instead with a dipole and just have a delta
match (no centre insulator… none needed).Â* There are many choices and
permutations, but in general, dipoles are centre fed at a point of current
maximum (and minimum voltage).
A normal dipole is current fed but of course can be voltage fed instead.
This is what’s done in the EFHWA or Fuchs aerial where a resonant half wave
wire is fed at one end (max voltage / min current) from an L/C tank,
against a very short counterpoise wire.

Original article is :W3DZZ Dipole Aerial design by the Maidstone Amateur
Radio Society

http://www.btinternet.com/~shaun.sca...club/w3dzz.htm

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