HF Random Wire Antennas

Resonant antennas have a lot of advantages: they are efficient, impedance matched to your transmitter and require minimal tuning. The main disadvantage of resonant antennas is that they are nearly always only usable over a single frequency band. Non-resonant antennas do not present a match on any band by default, however, they can be easily matched to a wide range of frequencies. One of the most common ways to match a transmitter to a non-resonant antenna is to use a 9:1 UnUn combined with an antenna tuner.

100W Random Wire

I built this version for field use and wanted to make the design as flexible as possible. To this end I built the antenna such that I can easily lengthen it when extra room is available. The default length is 53 feet and the antenna can be extended to 124.5 feet. These lengths were chosen because they are not resonant on any ham band. The 9:1 UnUn for this antenna uses a FT240-K ferrite toroid wound with 18AWG enamel wire. The UnUn is mounted to a DX Engineering Balun Bracket to provide a mounting point and antenna wire strain relief. The antenna extension was made by using two DX Engineering Wire End Insulators that are be bolted together for strain relief and Anderson Powerpoles for the electrical connection of the 14AWG antenna wire. For a counterpoise I made two 50 foot lengths using 24AWG speaker wire. I can also use the shield of the feedline coax and then isolate the antenna from the transmitter using a 1:1 Balun/Choke. I have used this antenna using only the 53 foot section of wire and was able to tune all of HF and made a few contacts using my HF Go Kit, although some bands required adjustment of the counterpoise length in order to be in range of the Yaesu FT-450’s antenna tuner.

QRP Random Wire

After experiencing some success with my high power version I decided to build a QRP version. The QRP 9:1 UnUn uses a FT140-43 ferrite toroid and is wound using 24AWG enamel wire. This combination should easily handle 10 watts. The physical construction of the UnUn itself uses the same strain relief technique as my End Fed Half Wave Matchbox, where 1/8″ acrylic is epoxied to the enclosure used to house the toroid. For this antenna I used 26AWG stranded copperweld and cut it to 29.5 feet with an additional extension to 53 feet. This should allow for quick and easy field deployment using my 31 foot lightweight fiberglass mast. I did some experiments with my QRP transceiver and my QRP Autotuner and was able to tune all of HF using this configuration and two 50 foot counterpoises.

Overall I think these random wire antennas are a good addition to my antenna arsenal. They are not necessarily the best option, however, they are very versatile and can prove useful when a simple multi-band antenna is required.

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