HF Resonant Loop Antenna
The antenna was built to be used for shortwave listening with a Tecsun PL-660 radio receiver. Later it was used with Yaesu VX-6 handheld transceiver and with Yaesu FT-817ND for shortwave listening. The antenna is mobile and sometimes I take it to SWL on the open air.
The antenna is built of two copper tubes. The tube used in the large loop, which forms a resonant LC circuit, is 10 mm in diameter and about 125 cm long. The small tube, which is used for coupling to the radio, is made from a 8 mm in diameter and about 28 cm long. The loops are not connected between them.
The variable capacitor is from an old AM/FM radio receiver. It has five sections: three sections of 30 pF which were used for FM band and two of about 430 pF previously used for AM reception. One 30pF section is constantly connected to the big loop while the other four can be connected using three tumbler switches (two 30pF sections are connected together). Connecting different sections makes it possible to get different maximum capacities.
The antenna tunes from about 6.5MHz (all the capacitors connected and at are set to the full capacity) up to about 43MHz. This tuning range makes it suitable for shortwave listening on 10-40 meters bands. The antenna shows very narrow bandwidth and has to be adjusted when receiver frequency changes by about 20-30 KHz. The sensitivity is not always high and sometimes it is outperformed by a long (~10M) piece of wire.
I've never used it for transmitting because my current amateur radio license doesn't permit transmitting on HF bands.
The first version was mounted on a plastic tube without any base to put it on.
Metal tubes, variable capacitor and tumbler switches:
The final version is mounted on a dust pan. On the photo: antenna, Tecsun PL-660 receiver and my favourite Parker "51" fountain pen.
The pan is used as a base and some stones put on it make it stable.
You are more than welcome to contact me with any questions, suggestions or propositions regarding this project. You can:
73 de 4X5DM ex 4Z7DTF