Completed 9:1 UnUn

These are sometimes known as a Magnetic Longwire Balun. Its really an impedance transformer (9:1) to feed a high impedance, end fed (unbalanced) random wire which is likely to be a few hundred ohms, and transform it into something closer to a 50Ω (unbalanced) coaxial input, hence UnUn. It can however also be used as a balun by not grounding the other half of the balanced output. The toroid is a T130-2 Iron Powder core, with 3 x 9 turns of 18SWG enammeled copper wire, and the connections can be seen below.

The triple winding connections. 8 turns is shown here, but more turns is preferred. 10 would be ideal.

9:1 UnUn Schematic

Completed windings

The completed unit.

This page contains some balun / unun / impedance transformers which I have built. This page is still being built.

Impedance Matching

• End Fed Half Wave Antenna Coupler – Using a parallel tuned circuit to feed an end fed half wave antenna.

Current (choke) Baluns

• 1:1 Choke Balun – For use as a ‘tuner balun’ on the output of an unbalanced ATU for feeding a multiband doublet.
• 1:1 50Ω Choke Balun – Built with coax, to keep the impedance at 50Ω for feeding a coax fed half wave dipole.

Voltage Baluns

• 50 ohm 1:1 Balun – A simple 50Ω 1:1 voltage balun made from a ferrite core.
• 9:1 Magnetic Longwire Balun / Unun – A 9:1 impedance transformer for feeding end fed wires.

This page contains projects and electronic circuits that I have built. Some are amateur radio related, others not.

Antennas

• 70MHz Quarter Wave Ground Plane – Building a simple 1/4 wave ground plane antenna for the 4m band.
• 144MHz Portable Yagi Beam – A compact, portable 6 element 144MHz Yagi antenna. built for quick assembly in the field or up mountains.
• Magnetic Loop Antennas – Experimenting with a VHF magnetic loop and a larger HF one in the back garden.
• Carolina Windom – Construction details for a 20m (66ft) off centre fed ‘Carolina Windom’ multiband antenna.
• 20m Loft Dipole – A crude shortened monoband dipole that fits in the average loft. My first HF antenna!

Baluns, UnUns and Impedance Matching

• End Fed Half Wave Antenna Coupler – Using a parallel tuned circuit to feed an end fed half wave antenna.
• 50 ohm 1:1 Balun – A simple 50Ω 1:1 voltage balun made from a ferrite core.
• 9:1 Magnetic Longwire Balun / Unun – A 9:1 impedance transformer for feeding end fed wires.

Capacitive Touch CW keys

• Simple CW Touch Key – Super simple CW touch key solutions
• Capacitive CW Touch Key – Purchase a capacitive touch key circuit board to build your own CW key!

Amplifiers

• 144MHz Power Amp – A simple 144MHz power amplifier schematic.

Transverters

• 472kHz transverter – A design by Roger G3XBM, providing around 10w on 630m band.

Other stuff

• Rig Interface – An isolated PC/transceiver interface for data modes.

Not radio related projects

• 12v > 240v Inverter – A simple inverter project using a PIC microchip, some MOSFET’s and an old transformer.
• Alkaline Battery Charger – A low constant current source for experimenting with recharging non-rechargeable batteries.