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HOME BREW LONG -WIRE BALUN BY
Dr. B. LLOYD
I've played with making myself a
"home designed" long-wire magnetic balun, which basically consists
of a triple coil around a ferrite rod. Compared with a
professional bought unit, it is big, heavy and clumsy (about 200 mm
x 50 mm [8 x 2 inches]) but I'm quite impressed with
it., It is never less effective than an OCF antenna I
have up, often 10dB better, and several frequencies are +20dB, which
considering it is only 3 metres off the ground and I find that
Here you go!
All the credit needs go to
Patrick Smith, GW0MVR. I only have a Novice Licence as
yet, and am a fiddler of the 1st order, hence the balun fun.
Out of interest, I did some "ear" and "s meter" tests and
this balun ALWAYS outperformed a commercially bought toroidal
long-wire balun, so it is worth the build. Grounding the
balun / coax to a good earth made between 3 and 6 dB improvement
with QRM, even though the station was well-grounded.
disabled, (some left-side paralysis), and managed this project in
about 2 hours, so it should be a simple 30 minute project for a fit
person who has the relevant parts present before they
3.5 Metres ( 4 yards) of 7.5
amp (or higher) 3 core electric cable
Ferrite Rod Ã¢â‚¬Â¦ I used one
of No 14 core material, 200 mm (8 inches) long and 9,5 mm (about
1/3rd of an inch) diameter. Dimensions are not critical.
A length of PVC piping to suit -- I used 50 mm (2 inch) piping
2 end-caps for the PVC pipe
1 chassis mount female rf
connector (I used an SO239 to accept PL259 plugs, but many prefer
Silicone paste -- clear, waterproof
Amalgamating insulation tape
Ideally, for the winding
of the wire around the ferrite rod, get some assistance.
The thickness of the wire and the tightness of the coils around the
rod make the winding process unwieldy, and it is very difficult to
glue / affix the wire to the rod. Ferrite rods are
brittle, and easily snap, so the coil winding is a 2 person job.
Fill the rod with the wire coils. The more turns
you manage the better the bandwidth.
It pays to use
amalgamating electrical tape to hold the coils in position along
it's entire length. I did this in 4 x 2 inch sections,
with extra tape applied at each end where the greatest stresses
Strip about 10 inches of the outside insulation
away from the left end of the wire, and about 4 inches from the
right hand side AFTER the wire has been wound round ferrite
rod. Important: Keep each wire's individual
insulation intact, and ensure you don't cut into this insulation
when removing the outer insulation.
Waterproof Enclosure in PVC
Keeping the wires as short
as you can, and staggering the joins so that the wires cannot short
or arc easily, join then as in the diagram. LEAVE the
Brown Left and Green Right long at this time. (NOTE: USE ANY COLOR WIRE YOU HAVE
BUT KEEP THE SAME DESIGN)
Green Left - Blue Right
Blue Left - Brown Right
From the excess wire you have, extract about 15 inches
of the brown wire, and the green wire. Solder the
odd-length of brown wire to the centre terminal on the SO 239
socket. And the green length to the outer terminal of the SO 239
Drill 2 holes in end-cap #1, suited to the diameter
of the Brown Left wire. I drilled one hole centrally,
the other off-centre, as use-indicators by position.
end-cap #2 and fit the SO 239 socket to it, first feeding wires
through the mounting hole Ã¢â‚¬Â¦ there is a temptation to fit the socket
the wrong way Ã¢â‚¬â€œ resist it.
the rod with coils into the PVC pipe, leaving the wires poking free
from each end as relevant. Feed the length of the odd
piece of green wire soldered to the socket the length of the pipe.
Feed this green wire through the off-centre hole drilled in
end-cap one. Tie a knot in this wire so the knot will
sit inside the end-cap, and prevent strain if the wire is
pulled. Feed the Brown Left wire from the rod through
the centre hole of end-cap #1. Fit the end-cap to the
PVC pipe. Keep the "excess" wire that will be in the
balun to a minimum.
Again, using minimal lengths of wire,
connect Green Right to outside terminal of the SO239
socket. Solder the to the odd length of brown wire
that is attached to the centre pin of the socket to the Blue/Brown
junction on the coil.
Fit end-cap #2 to the pipe.
Seal all parts with the silicon, to make a waterproof
This is a low-power, 10 watts max, and it's always
advisable to use an ATU, but it will cover 1 -- 30 Megs
It pays to pack the
pipe innards to stop rattle, and endangerment of the
rod. If you do, use non-flammable for the
packing. If however you are making a receive only balun,
then the ideal packing is good old bubble wrap.
Connect a minimum of 23 yards of wire to the brown
wire sticking out of the top of the balun. I find 30
yards an ideal compromise.
You do not have to Earth/Ground
the Green wire sticking out of the top, but it helps minimize
interference if you do. Grounding the balun / coax to a good
earth made between 3 and 6 dB improvement with QRM, even though the
station was well-grounded
Long-wire antennas are
directional, so bend yours to allow both N-S and E-W
orientation. Height is dependent on your location and
Receive only, works well even at 3
ft off the ground. 73