2007 KØS, Strange Antenna Challenge

Satellite KØS Station

KC4ZUA/KØS

    These "Strange Antenna Challenge" photos are for my 20 foot extension ladder adjusted to a length of 16’ 5" for resonance on the 20 meter band. An SWR of 1.8:1 was measured during low power testing of the antenna. The radio I used for the challenge was an Alinco DX-70T with an output power of 100 watts. The ladder antenna was fed with coaxial cable from my screened in porch. The center conductor of the coax was fastened to the ladder with a sheet metal screw. The shield of the coax was joined to three chicken wire fence radials on an insulator made from a Georgia Pine 2 x 4. The ladder was held in the upright position by 4 screw anchors and cargo straps.

    73, Arnold Solomon, KC4ZUA

    Those chicken wire ground radials must have worked pretty well. A swr of 1.8:1 shows very nice ground currents returning to the antenna, forming what should have been a pretty efficient antenna, even for a "normal" antenna, let alone a "strange" antenna! Sweet!
~ Erik, n0ew

    These "Strange Antenna Challenge" photos are for my "Soda Pop Can Vertical Dipole" that is resonant on the 2 meter band. An SWR of 1.7:1 was measured during testing of the antenna. The radio I used for the challenge was a Kenwood D700 with an output power of 5 watts. The cans were fed with Teflon coaxial cable from my operating position below. The coax was joined to the cans with sheet metal screws tapped into a short sleeve of PVC pipe. Each can was fastened to the can below it with 3 sheet metal screws to form an antenna element. After measuring a number of different can types, I determined that a stack of 4 aluminum soda pop cans was within 0.2" of the calculated value for a ¼ wavelength element.

    73, Arnold Solomon, KC4ZUA

    Strictly speaking the Strange Antenna Challenge takes place on the HF amateur bands. One reason for this decision is metering equipment typically available to amateur radio operators is much less accurate at the higher frequencies (errors of 20% or greater are common), and many 2-M/440 radios are not as resilient as HF radios when loading into large impedance mismatches. Therefore you are both more likely to damage your 2M/440 radios, and less likely to be able to accurately measure the antenna system with great precision. You are certainly welcome to experiment with these higher frequencies, but please exercise greater caution with your equipment because 2M/440 XCVRs are much more likely to be damaged than HF XCVRs under these experimental conditions.

    We do, of course, recommend utilizing caution even with your HF transceivers. "Tube" rigs are generally quite versatile. That "dip and peak" business is essentially an "antenna tuner" inside the XCVR. Properly loaded into the antenna, strange or otherwise, they should work quite well for an extremely wide range of antenna radiating elements. "Modern" IC-based transceivers are almost all designed to load into a near 50-Ohm antenna system. But because the XCVR itself can not modify its output impedance to match a very wide-range of impedances, many manufacturers build in a "self-protection" circuit. This reduces power (or shuts off) the XCVR when it is operated under too severe a SWR mismatch. (To my experience such self-protection seems to engage around 1.5:1 to 2:1 SWR.) This means IC-based XCVRs may require more care in matching the impedance the antenna system presents to the XCVR. Not all IC-based transceivers have "self-protection" circuits. Verify whether yours does, or does not.
~ Erik n0ew