The LEK LowFER Antenna

The picture of the KØLR antenna farm on my home page provides a general view of the farmyard. There is a free-standing 64-foot tower behind the house, and a guyed 57-foot tower to the right of the garage (a large metal pole building between the house and barn, mostly hidden behind some arbor vitae bushes that have gotten out of hand). As ham installations go, my antennas are pretty simple. A couple of homebrew 2-meter yagis on the tower next to the house, and wire dipoles for the HF bands. The antenna for beacon LEK, shown below in a close-up view, is a "flat-top" that is suspended between the two towers and more or less centered above the garage roof.

Like the picture of the farm on the home page, the close-up of the LEK antenna was taken when there was a heavy coating of frost on the wires, which makes them visible against the sky. The top hat consists of two 15-foot aluminum spreaders and two 30-foot #14 "Flexweave" copper wires. I used Flexweave so the whole thing could be hoisted without getting hopelessly tangled. There are four #14 Flexweave downleads, connected to a single vertical wire that goes down to the loading coil, which is supported 4 feet above the garage roof on a piece of PVC pipe. Total "length" of the antenna, as measured from the roof to any corner of the top hat, is about 46 feet. It was supposed to be 49.2 feet (15 meters), but the thing sags more than I'd hoped it would. There is an SO-239 connecter in the roof, and the final amplifier is mounted just below the roof inside the garage. The main loading coil I used for the past several years is 18 inches diameter by 9 inches high, and is basket wound with 65 turns of #14 insulated building wire. Its inductance is about 2.5 millihenries. A smaller tapped inductor inside the garage was used for fine tuning. In early November of 1998 I replaced the big coil with a smaller coil, 9 inches diameter by about 5.5 inches long, wound with 120 turns of what appears to be 50X38 Litz wire. This new coil has a Q of about 700, as compared to about 500 for the old coil, and an inductance of 3 millihenries. This inductance is greater than needed to resonate the antenna at 186.75 kHz, and a series capacitor of approximately 4000 pF (3300 pF fixed in parallel with a 1000 pF variable) is used for tuning. An upside-down 5-gallon plastic pail covers the coil to protect it from the weather. Measurements with and without the polyethylene pail in place show very little difference in inductance or Q. The exciter for LEK is in the house, with about 100 feet of coax carrying the exciter signal to the final. LEK's final uses the complementary-pair output circuit shown in the "Simple LowFER Transmitter", and a similar circuit is used in the exciter to drive the long coax run to the final.

The only ground system for the LEK antenna is the 30 by 44 foot metal roof of the garage. This seems to make a fairly effective ground plane. I haven't made any special effort to bond the panels of the roof together electrically, except to add two or three galvanized roofing screws to each joint within the past couple of years. Antenna system losses are fairly high in the summer, with a total resistance of 20 to 25 ohms. In winter when everything near the antenna (including me) is frozen, the losses drop to about 15 ohms.

Other "wires" in the picture are actually 3/16-inch UV-resistant Dacron rope, which is used for the bridle and support lines, as well as the guy ropes for the 57-foot tower behind the garage. The 57-foot tower is also insulated at the base so that it doesn't act like a shunt capacitor from the LEK antenna to ground. There is a pulley at the top of the 57-foot tower with a halyard and a heavy counterweight so the antenna can sag if it becomes loaded with ice or wet snow. During the first few wind storms after the tower was, the guy ropes stretched a lot and there were some very anxious moments. However, the whole antenna has been up for over five years now, and the ropes do not show much sign of deterioration.

To date, LEK's CW signals have been heard in Minnesota, Wisconsin, Iowa, North and South Dakota, Illinois, Ohio, Michigan, Kansas, Missouri and Oklahoma. Two-way contacts have been made with YB, CRL, ART, and TO, all in the Twin Cities area about 100 miles from me, and with BK (Wisconsin), BA (Illinois) and XJ (Ohio). The greatest distances covered were about 750 miles for reception of my beacon signal (Bill Bowers in Oklahoma) and about 730 miles for a number of two-way contacts with XJ (WA8LXJ) in Ohio. Nothing record-shattering, but fairly good DX for a couple of milliwatts of effective radiated power.