Message 21394 in TECH.WW
From: G8MNY
Date: Sat, 25 Apr 26 08:22:00 Z
Newsgroups: TECH.WW
Subject: 2m Fullwave Dipole
Message-ID: <58074_GB7CIP>
Path: N2MH4|N3HYM|IW2OHX|GB7CIP
R:260425/0830Z 30589@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260425/0830Z 3159@N3HYM.#FRDK.MD.USA.NOAM BPQ6.0.24
R:260425/0829Z 5328@IW2OHX.ILOM.ITA.EU BPQ6.0.25
R:260425/0822Z @:GB7CIP.#32.GBR.EURO #:58074 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have a design for a fullwave dipole. It is only suited for loft environments
as it is made from 2.5mm bare copper wire hanging from the roof apex, & giving
vertical polarisation.
LOFT APEX
string
The half waves are both 1M long, & the 2 matching lines are 2cm apart, & are
just over a 1/4 wave long. There is a plastic insulator (Chock block) at the
feed connections.
half wave of coax (x velocity factor 0.8 or 0.66). All the coax braids are
joined to each other but nothing else. The feeder inner is connected to the
start of the half wave 4:1 balun, & the load (chock block line taps) connected
across either end of the half wave phase reversing balun coax.
All Braids Joined
When the line tapping point (impedance) & shorting point (tuning) are adjusted
The advantage of this design is it can always give 1:1 SWR even if the lengths
are not quite right, or the aerial is being de-tuned by the roof, & being a
symmetrical centre feed system all the power should go out to the horizon.
The feeder must be taken away horizontally to the roof & then down so not
interfere with the very tight horizon radiation pattern.
___ ___ _---_
/~ ~\ /~ ~\ /~ ~\
\_ _/ \_ _/ \_ _/
~~~ ~~~ ~---~
Gain to the horizon is substantially more than slim jim or 5/8 wave aerials.
The design can easily be made into an outdoor version with solid tube for the
elements & TV aerial booms for the matching lines with the shorted end clamped
to a pole. Other band versions are also quite easy to construct.
Why don't U sent an interesting Bul?
73 De John, G8MNY @ GB7CIP
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