|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
Here you go!
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.
I’m 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 start.
3.5 Metres ( 4 yards)
of 7.5 amp (or higher) 3 core electric cable
Ferrite Rod … 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.
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 BNC connectors).
Silicone paste –
clear, waterproof outdoor variety.
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
Enclosure in PVC Pipe:
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
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 socket.
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.
#2 and fit the SO 239 socket to it, first feeding wires through the
mounting hole … there is a temptation to fit the socket the wrong way –
Insert 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
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.
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.
parts with the silicon, to make a waterproof enclosure.
This is a low-power … 10 watts max … and it’s
always advisable to use an ATU, but it will cover 1 – 30 Megs effectively.
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.
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
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 surrounds … experiment!!
works well even at 3 ft off the ground.
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