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G8MNY > TECH 05.07.07 22:30l 60 Lines 2762 Bytes #999 (0) @ WW
BID : 21371_GB7CIP
Read: GUEST OE7FMI
Subj: Simple 1/4 Wave 2m Mobile Aerial
Path: DB0FHN<DB0NOE<DB0GAP<DB0GPP<DB0LX<DB0SEL<DB0ZDF<DB0GE<DB0LJ<DB0RES<
DK0WUE<7M3TJZ<ZL2BAU<N4JOA<VE3KPG<GB7CIP
Sent: 070705/1953Z @:GB7CIP.#32.GBR.EU #:21371 [Caterham] $:21371_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Jul 07)
This is the simplest aerial always to have in the car as a spare. It works on
both 2m & 70cms. Although it is a 3/4 wave length on 70cms, 2 of those 1/4
waves are in opposite phase, so giving only the gain of a 1/4 wave. As it is
just a coat hanger it can be bent out of the way & straightened as needed.
CONSTRUCTION
It is made from, "Coat Hanger Wire" or similar fencing wire. soldered into a
standard PL259 plug. You will need a piece or wire at least 20 inches long to
allow for trimming.
Grease
\ ÄÄÄÄ¿/
ÃÁÂÄÄÄÄ¿ Paint the wire if you want no rusting!
.----Á-|_____\______________________________________________________.-.
Solder/'----Â-| / '-'
Pin ÃÂÁÄÄÄÄÙ \ Fill whole plug After tuning
ÄÄÄÄÙ top with heat glue up add heat
PL259 & cone top off. glue ball tip.
To solder to galvanised steel is straight forward with some solder fluxes, if
not with yours you will have file the wire to provide keys for the solder to
grip the wire.
MOUNTING
Before you attempt tuning up the mounting & location is often critical for a
good SWR.
239 Magmount 239
__ÚÁÁ¿__ Gutter Mount 239 Socket
239 _..--~~~~ Apex ~~~~--.._ÚÁÁ¿ drilled in roof! 239
window / of roof \Ù_³ --ÁÁ----...__ Tail gate
ÁÁij \/ÁÁ Mount
³ \
So choose the best option for you. Remember there are low garages to enter,
but also you gain about 6dB more Tx & Rx signal for each doubling in height!
Note that ideally the mount should make a good electrical connection to the car
body, but often the close fittings give high enough capacitance, like in the
magmount example. If a non metal body use 1/4 wave ground planes in wire or
stick on foil such as alarm tape.
TUNING UP
Start at the lowest frequency & measure the SWR on 2m, then trim a piece off
the aerial (say 1/2") remeasure. As log as the SWR is improving reduce the
length, & use smaller lengths to cut off. When SWR is OK then test on 70cms
it will be far more critical on that band. Test on the centre of 2m band & if
SWR is higher trim some more retest 70cms as well.
When done remove aerial & make a bobble of heat glue on the end & rotate aerial
to make into a ball over a heat source. Cool off in water. Paint up aerial.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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