Long Wire Antenna 1:9 Balun for 3-50 MHz (by F4HWK)

by kavea

21K459

Intro: Long Wire Antenna 1:9 Balun for 3-50 MHz (by F4HWK)

Here i present the fabrication steps for a long wire balun having a transformation ratio of 1:9. This balun is simulated with LTSpice and measured with a VNA. The power handling has also been tested with a 50 W (SSB) of injected power without any problems.

Simulation results are available on my blog : http://kavea.free.fr

STEP 1: Materials

Ferrite toroids FT114-61 (2 pcs)
Copper wire, 1 mm diameter, 35 cm length (3 pcs)
RF connector (e.g. SO239) (1 pc)
Butterfly screw (1 pc)
Any enclosure box (1 pc)

STEP 2: Wire Winding

Wire winding should be done around two FT114-61 toroids (cf. photo) with the respect of the scheme (cf. photo). Wires should have some isolation coating (e.g. enameled wires).

STEP 3: Enclosure Box

In my case i used a 50 mm diameter PVC tube to enclose the balun. Solder corresponding wires to the RF port and to the butterfly screw (cf. photo). Now the balun is fully assembled.

STEP 4: Measurements

To check the transformation ratio of 1:9, the balun has been measured with a VNA. In this measurement the balun is connected to a 470 ohms resistor (the impedance of the VNA port is 50 ohms).

As we can see on the picture, the balun assure a bandwidth going from 3 MHz up to 50 MHz with the respect of SWR of 2:1.

The balun has been tested with an output power of 50 W without any problems.

7 Comments

athomp58 3 years ago

AWG 18 gauge thermostat wire works great for this project. Cut off a 15" piece, discard the outer jacket, voila, color coded wires with thin insulation that will easily wrap onto the ferrite! Also, I glued the ferrite cores together with E6000.
Thanks for this project, Kavea.

hc1pe 5 years ago

Hello, I have two 140-61 ferrite toroides, it is possible to build with your 1:9 balun model, how many turns for 100 watts?

RICHARDM433 6 years ago

Can this be used in a car? I have purchased a antenna booster with no results although it had 4 star rating!

kavea 6 years ago

Yes it can be used anywhere, the best antenna booster is the antenna itself. You are operating on HF in your car ?

tytower 6 years ago

So are you saying you can attach a tranciever to the balun and safely transmit on any frequency from 3 to 50 megahertz or do you still need a tuner in there somewhere?

kavea 6 years ago

If your antenna has a stable impedance of 450 ohm over 3-50 MHz, than you don't need a tuner, otherwise you still need a tuner, but this balun helps a lot to tune wires to 50 ohm. In my case i can easily tune a 5 m length wire to 80 m band with LDG 100 tuner, without this balun i cannot tune this short wire. Another advantage to use the balun is some common mode rejection which decrease the radiation from the coaxial cable.

To increase the power handling up to 200 W you need one FT240-61 toroid, it has the same AL of 170 as two FT114-61, so this should give the same result, but with increased power handling.