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G8MNY > TECH 09.05.20 12:12l 66 Lines 2669 Bytes #999 (0) @ WW
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Subj: 13cms Dipole & Reflector
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By Dick VK3ABK (Tech list on Apr 07)
Roy, ZS6MI, has asked for details of a 2.4GHz 'antennae' (!)
I take this as a challenge, but with some reservation.
Hey, Roy. Insects have 'antennae', Hams have 'antennas'!
But just to stay friends, here is a suggestion for your flat plate antenna.
³ ³
ÄÄÄÄÄÄÄÄÄÄÄ´ÚÄÄÄÄÄÄÄÄÄÄ <-- 2.4GHz Dipole
³³³
³³³
³³³ <--Tube with centre conductor
³³³
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÁÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄ <-- GroundPlane
³
Coax
A dipole for 2.4GHz (300/2400 X .95 divided by 2 = 5.9 cm) can be made from any
stiff copper wire, one half soldered to a copper or brass tube, say 10mm OD
which would be about 8mm ID, & the other half soldered to a centre coaxial
conductor. This is done down the end of the 10mm tube,which is big enough for a
60 Watt soldering iron. The 8mm ID tube & a 3.5mm centre conductor, near enough
to 1/8 inch welding rod, would give you a 50 Ohm transmission line (Z = 138 log
D/d) near enough for the dipole.
This forms a 'stub fed' dipole at onequarter wave (half the dipole dimension
will do) from the ground plane, or plate, of any large dimension. The
advantages of this construction are, an electrically & mechanically solid
construction, with an inbuilt support for the dipole that is 'electrically
ground' at the ground plane support. The antenna is easily water-proofed, or
can be mounted inside a plastic cake box or similar.
I just worked this out as an exercise to show how you can design an antenna
from 'principles', rather than looking up texts & many formulas.(formulae?!)
You could be more fundamental (& domestic) & you just want to see if WIFI can
be received, by using a toilet roll tube wound & spaced with 3 or 4 turns of
wire to form a 2.4 GHz helix (just the right diameter for a full wave) & mount
this alone or on a ground plane.
Many ways to spend a cold night playing with microwave antennas, & using an
array of dipoles mounted on a 'flat plate' is a good way to go.
Hope this helps.
73. Dick. VK3ABK.
-----------------
Y don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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