QRP: Low-Power Communications

…and Analysis by WB6UTW

In July 2018, CQ featured the article “The Sabretooth Wire: An Innovation in Antenna Length Shortening” by Eric Knight, KB1EHE. Eric’s sabretooth wire design significantly reduces the length of a wire antenna by kinking the wire so it looks like a “sabretooth” or a triangle wave on an oscilloscope. As a QRP operator who enjoys low-band operation from portable locations, Eric’s idea inspired me to make my own sabretooth wire (Photo A) for constructing a shortened half-wave, inverted-V dipole covering 10-80 meters.

Details on how I made my own sabretooth wire from 22-gauge wire and clear packing tape for an inverted-V dipole, which I nicknamed the Sabre-V, are highlighted in the October 2019 QRP column. To ensure the antenna would cover 80 meters, I calculated the length of a half-wave dipole (468/frequency [MHz]) using 3.5 MHz then added a few feet since I was unsure how the zig zags in the wire would react during tune-up. I settled on a length of 140 feet of wire (70 feet for each leg). It is important to note that I feed the Saber-V with approximately 50 feet of 300-ohm window line in concert with an antenna tuner (with a built-in balun). I prefer not to use coaxial cable because of its loss. My antenna tuner (MFJ-971) allows me to use the Sabre-V as a multi-band antenna (10-80 meters), including the WARC bands (12, 17, and 30