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 impressive!
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.

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.

Parts List

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.
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 BNC connectors).
Silicone paste – clear, waterproof outdoor variety.
Amalgamating insulation tape


Construction

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 would apply.

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 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
   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 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.

Drill end-cap #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 – resist it.

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 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 enclosure.  

Comments

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.

Using it!

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 surrounds … experiment!!

Receive only works well even at 3 ft off the ground. 73!

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