2004 KØS, Kurt N. Sterba Strange Antenna Challenge

Operated by Erik Weaver nØew and Dwayne Walker wb5plj,

Truck Dipole - Suburban & Blazer

Icom-746, 60-Watts, MFJ-962D Versa Tuner III, Battery Power
May 30, 2004

   We made our only DX contact with this strange antenna, VE3FDK in Ontario, Canada.

   Yes, it's a classic! No, not the trucks, although I guess they are getting close to becoming antiques, I'm talking about the truck dipole! We backed up our trucks close to one another and hose clamped the ends of the breakout wires to the 2-inch receivers on each truck. This required two hose clamps connected together to reach all the way around the hitch, but it loaded up and we did make a few contacts.

   We were telling people we were transmitting at 100-watts, but afterward we noticed the battery had run down to the point we were actually transmitting at only 60-watts. Speaking of batteries, we disconnected the batteries in the trucks just to be safe, and I disconnected my 2-meter radio from its power source. Neither one of us has a big whip antenna, or any HR antenna for that matter, on our trucks.

   We were calling CQ on this antenna for over an hour but only made three contacts. We made a couple contacts out west, New Mexico and Nevada, and of course Canada. We made each of these contacts on 20-meters. This would seem to be a fairly poor result. Only the loadlock dipole made fewer contacts (by one).

   If you'll take a look at the SWR chart, you'll notice that 20-meters shows a pretty good SWR. Should work great right? Well, take a closer look at the resistance and reactance notes along the bottom of the chart - 14.300 MHz shows 14-Ohms, and 11-Ohms respectively. Not very much reactance which is good, but the resistance is not all that high. Nowhere near the 73-Ohms a "real" dipole will show (provided it is high enough above the earth), but it does compare favorably to mobile antennas (pardon the pun).

   Perhaps the polarization was wrong?

   Well, since this is HF I rather doubt it. By the time the RF signal bounces off the earth and atmosphere a few times I don't think it would matter too much what the polarization was (vertical or horizontal).

   We are however only a few inches off the ground. This extremely short antenna height (say 4 inches) should have some negative affects upon our attempts to make distant contacts:

1. We are experiencing a large degree of ground losses, a real worm warmer. Because our antenna's height above Mother Earth is only a few inches, much of our RF energy is being absorbed into the earth. (Great looking SWR though! -- low SWR for the wrong reason! ;^)
2. Our resistance is on the low side, at 14-Ohms this is giving us about 1/4th the resistance we really desire (we want 50-Ohms so our transceiver and transmission line can fully load into the antenna).
3. Last, but not least, this is definitely a NVIS antenna (as were all our strange dipoles this weekend). Most of the RF energy we are radiating is likely taking off at a pretty high take-off angle (of course I don't have antenna modeling software that can handle this, but would welcome such efforts by our readers). Low take off angles are good for talking greater distances, whereas higher take-off angles favor local contacts, roughly in a several hundred mile radius.

   Now I'd expect 15-meters would have worked pretty well, although the low height will always create a compromised situation. The resistance was basically a perfect 52-Ohms, and there was not very much reactance present (22-Ohms). I don't recall if we called any CQ on 15-meters or not. We didn't make note of where we did not make contacts or where we called CQ without any reply.

Please note of the little gray boxes adjacent to the 5:1 SWR line. These indicate the approximate location of the amateur radio bands from 160- to 6-meters. This allows us to gain an impression of how each antenna shapes up across the entire HF range in which our amateur radio bands reside.