Topband: Inverted "L"
Thu, 26 Apr 2001 19:37:54 -0400
> If you want to go multi-band, you can put traps in the wire at 33 feet
> and about 58 feet for 40 and 80 meters like K1ZM did with his wire
> version of the Battle Creek Special with traps made of 50 ohm coaxial
> cable. It is written up in ON4UN's latest Low Band DXing book. Start
> with longer wire lengths and trim to suit. The reason I said about 58
> feet is the 40 meter trap will give one about 8 feet of inductive
> loading on 80 meters.
I'm giving a talk at Dayton on Friday in the antenna forum on traps.
I've spent some spare time in the past several months building and
measuring traps...and testing traps other people have sent me.
The talk is based around measurements of actual traps, and
included will be measurements of actual 80 and 40 meter coaxial
traps. I'll give a circuit equivalent of various traps that you can plug
right into EZNEC for Windows.
It is very revealing to plug equivalent values of traps into models
before building trap antennas, especially if you plan on using traps
made from coaxial cable!
There is a large difference between coaxial cable traps, and one
made with normal lumped components. The best traps use
components like airdux inductors and transmitting-style capacitors.
The worse? Coaxial traps...by a very large margin.
73, Tom W8JI
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