Spokane DX Association

The 43 foot vertical

Many different companies are joining the bandwagon and offering a 43 foot vertical antenna. This is touted to work the ham bands 160 to 10 meters. The big question is how well does it work on these bands?

Ham radio is full of stories how stations (even DX) were worked using window screens, bed springs, and even light bulbs as antennas. I helped an apartment bound blind friend use his rain trough as an antenna when he was prohibited from using even a small vertical. N6BT of Force 12 fame worked many stations using a light bulb antenna.

What is so special about a 43 foot vertical? It happens that the impedance at the feed point is in the range of 100 ohms to 300 ohms except on 80 and 160 where it is very low resulting in very poor efficiency. Use a 4 to 1 un-un and you may be able to use your xcvr internal tuner to operate. Notice I said un-un not bal-un. Some of the antennas are being supplied with a bal-un which is a serious mistake (Zero-Five). That will cause your coax outer shield to be part of the radiating antenna and couple unwanted RF into your ham shack.

This antenna is a respectable performer on 40 thru 20 meters with a good radial system. On the lower bands the very low feed point impedance and our inability to make a long enough radial system (in wavelengths) make it a very poor performer. On the bands above 20 meters the radiation angle is too high, because it is too long, making it a cloud warmer.

The best thing you can do to optimize the antenna is to put an efficient matching network at the base for each band and install a good radial system. There was a 2 part article by Salas in a recent QST which does a good job of showing how to do this. If you want to know a great deal more about this antenna, including calculated efficiency for different configurations. See the work that VK1OD did here. http://vk1od.net/antenna/multibandunloadedvertical/index.htm”