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## Topband: How Helically Wound Verticals Really Work

 To: Trent Fleming Topband: How Helically Wound Verticals Really Work "Richard (Rick) Karlquist" Wed, 15 Jul 2009 21:46:18 -0700 mailto:topband@contesting.com>
 ```Trent Fleming wrote: > In a recent ham magazine, there is an article about an HWV for 160m I am > very interested in having an antenna for 160m, and in having a vertical for > the low bands in general. If I were to build this HWV, are there any > techniques I should consider to get it to perform well on 80 and even > perhaps 40m? Or am I being greedy and just need to focus on the HWV > Trent > N4DTF > The concept of the helically wound vertical (HWV) is appealing: no lossy loading coil, just a low loss wire. The "proof" of this is that you can run a kW and the antenna does not get hot. It is easy to see why this antenna is popular. The reality is different. The HWV does not eliminate the loading coil, it just replaces it with a very long skinny coil that runs the length of the antenna. The radiation resistance of the antenna is not affected by the coil. However, the Q of a long skinny coil with wide spaced turns is much less than a conventional coil. This is simply because it takes a lot more wire to make the coil. In the article, over 250 feet of wire are used; much more wire than is required for a conventional coil. If you want to prove it to yourself, just do a few sample calculations using Wheeler's inductance formula, which is in every radio handbook. You will see that if the length of a long skinny coil is doubled, the amount of wire needed goes up about 40%. The loss per foot of wire is basically independent of spacing if it is at least a couple of wire diameters. Therefore, the loss goes up 40% with each doubling of length. Also, winding the coil on PVC pipe introduces additional losses due to the PVC. Since the wire is distributed over the whole length of the antenna, the great amount of additional heat is not apparent because it is spread out so much. The radiation resistance is only a few ohms, but the wire resistance may be many times the radiation resistance. This improves the SWR (if not using a matching network at the base) and broadens the bandwidth, but lowers the efficiency. The antenna then appears to be satisfactory with a decent match and decent bandwidth and able to handle high power. The low efficiency may not be apparent since it is still possible to make QSO's. It may compare favorably to a low dipole ("all" dipoles are low on 160 meters) simply because, in many cases, low dipoles don't get out very well. It may even be possible to work DXCC with an HWV. We know that doesn't prove high efficiency because KH6DX has achieved 160m DXCC operating mobile. His antenna is a very good mobile whip, but it is certainly down 10 dB from an efficient antenna. Don makes up for low efficiency with QRO and persistence. BTW, Don doesn't use an HWV. It's not like an HWV is the only antenna you can put up on your city lot. It's actually easier to just use an aluminum vertical with a conventional coil. Why go to the trouble of making an HWV? I see lots of coils going begging at every swap meet I go to. The aluminum can be smaller diameter than the PVC, which may allow you to get away with more height. PVC is a lousy structural material. You will need a matching circuit, and the antenna bandwidth will be less than an HWV. Now as to the question of 80 and 40 meters, that will not work with an HWV, but is easily done if a conventional loading coil is used. Just change the tap to QSY. Some advanced systems use a motor driven roller inductor to do this. Rick N6RK _______________________________________________ Topband mailing list Topband@contesting.com http://lists.contesting.com/mailman/listinfo/topband ```
 Current Thread Topband: Helically Wound Vertical, Trent Fleming Re: Topband: Helically Wound Vertical, DAVID CUTHBERT Re: Topband: Helically Wound Vertical, DAVID CUTHBERT Re: Topband: Helically Wound Vertical, Gerry Hohn Topband: How Helically Wound Verticals Really Work, Richard (Rick) Karlquist <= Re: Topband: How Helically Wound Verticals Really Work, Dan Zimmerman N3OX Re: Topband: How Helically Wound Verticals Really Work, Rick Karlquist Topband: HELICALLY WOUND VERTICAL, CRAIG CLARK Re: Topband: HELICALLY WOUND VERTICAL, DAVID CUTHBERT Topband: f IRe: HELICALLY WOUND VERTICAL, Jim Brown