Here some info on loading coils and current distribution in loaded resonant antennas. http://www.k3bu.us/loadingcoils.htm In the nutshell: efficiency is roughly proportional to the area under the current curve along the radiator. It is better to have loading coil or top loading than distributed helical.
Yuri K3BU.us ----- Original Message ----- From: paulkb8n Date: Thursday, March 31, 2011 2:36 am Subject: Topband: 160M Helical Vertical To: [email protected] > I've read a lot about the K6MM vertical and may be forced to go > that route, as the Neighborhood Association has received some > complaints on my current 160M dipole and I may be forced to > remove it. > > Somehow, I feel that the K6MM design might be improved. I've > been testing an 80M version using some military-style fiberglass > mast poles with my helix made out of copper foil tape. This has > resulted in a much more tidy and easier way to construct the > helix. I also believe the 1.5 mil foil has less capacitive > losses between turns than the wire that is used by K6MM. I am > using a one-quarter inch wide foil tape on my 80M version, and > with fairly close spacing and a small capacitive hat, I can > squeeze the antenna size down to only 8'. > > I've been testing this antenna indoors in my attic, and it seems > to work remarkably well. I've gotten decent reports around the > states, and have worked some modest DX. > > I have no idea how the foil tape helix could be modeled. I have > built several working helical segments using various diameter, > tape size and pitch, and measurements suggest that using a half- > wave of foil tape in the helix will yield a quarter-wave of > electrical length. Every design I've tested seems to show nice > usable bandwidth against a fairly decent ground (center screen > and 12 radials). I am wondering how the flat foil tape will > perform compared to a regular round conductor? Also, what width > of foil tape would be adequate for 160M use? Has anyone modeled > or experimented with this? Can the > > My 80M version's performance gives me hope that a short 160M > helical vertical might work effectively as well. Any thoughts > or suggestions will be appreciated. > > Thanks, Paul, K5AF > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
