FM Broadcast Antennas

At my old crib, I could get what was probably the best radio show I’ve ever heard, in any genre. This was a heavy-metal radio show by Earl Root. 1am to 6am Saturday night, on KFAI 90.3.

Unfortunately, KFAI doesn’t give a damn about rural listeners, and their antenna pattern sucks for anything north of the cities. All through 1999, I worked at putting up a good enough FM antenna system to get at least a wisp of signal from them, 80mi distant; but to no avail. Sigh…

Besides the low-signal problem, there are also a couple of obnoxious NPR ‘repeaters’ east and west of me on the same frequency; which makes back and side lobe rejection also a prime antenna design concern.

So, no heavy metal radio for me any more, but in any case, here’s a record of the efforts made.

Phase 1, a 3-el quad:

This one was so ugly, I never even took pics of it. It also was never tuned using test equipment, and it never worked worth a damn.

Phase 2, a 5-el quad, done right:

This one worked quite well on other stations up to 100mi away, but not a whisper from KFAI.

This quad was constructed of wood-dowel spreaders, a 1×2″ boom, and #18 enameled wire elements.

Phase 3, a Yagi for 90.3

After the disappointment with the 5-el quad, along with the realization that the many obnoxious NPR repeaters were going to be a problem, I set the project aside for a while. The next time I got motivated to try again, I chose a Yagi style as giving me the best hope of excellent rear and side rejection, along with reasonable gain. I did quite a bit of research into Yagi design and ended up with an antenna that worked extremely well.

The results of that research….

This Yagi-Uda is constructed of #8 aluminum wire elements mounted to a 1×2 wood boom. I employed a variable-length coax-balun section to accomplish both impedance-matching and balance-to-unbalance in one device.

Also visible in this picture is a low-noise preamp I built after this antenna alone failed to pick up Mr. Root. Unfortunately, the preamp didn’t snag Mr. Root from the ether either, but this antenna/preamp combination worked extremely well. With it mounted on the 40′ tilt-tower, I’m able to listen to FM stations from Iowa, Wisconsin, South Dakota, and all over Minnesota.

That ends the FM antenna saga….for now….

After Ray (WA9SXJ) comes up in the spring and installs 150′ of Rohn 55, I’ll give it another shot!