Dear Friend, Since Episode 4 of the QSO Today podcast, with Rich Fusinski, K8NDS, I have desired to build a magnetic loop antenna. These antennas are ideal for limited space, work from the ground, have a low take-off angle for working DX, and are small in size. In addition the loop is 1/10th of a wavelength on the frequency band that you want to use it on. This means that you could build a 40 meter magnetic loop antenna using a loop that is 1 meter in diameter.
These antennas are not without their challenges. They are tuned circuits with a very high "Q". They need to be tuned exactly for the transmitting frequency. At 100 watts, the high voltage generated at the high voltage points around the loop is in kilo-volts requiring a very expensive vacuum variable capacitor. Any resistance between the loop and the capacitor will cause problems when transmitter power is applied.
My guest this week, Steve Adler, VK5SFA, built and won the 2018 QST Antenna Design Competition by building a 160 meter magnetic loop antenna. Imagine that 1/10th a wave length on this antenna is 16 meters, or about 6 meters in diameter if using a single loop. Steve reasoned that as the antenna is a tuned circuit, he could make his antenna loop twice to reduce the antenna diameter. He had all of the magnetic loop challenges discussed above and a much bigger antenna for the 160 meter band. As it turned out, his antenna was a big success, allowing him to work DX on 160 meters from Australia.
To me, these antennas are fascinating and Steve's story about this project is one of the best segments in this interview. He also tells a story about a noise problem with a neighbor's LED lights t towards the end of the interview. This is a great lesson for all of us who live in neighborhoods with other people while trying to successfully operate our radios.
Thanks for listening.
73, Eric 4Z1UG |
