[Elecraft] Trap designs with toroidal inductors

[N2EY@aol.com]

In a message dated 11/16/02 10:36:50 PM Eastern Standard Time, Mike@crv.com 
writes:

>  Can anyone on this list point me toward any references that discuss trap 
> construction using toroidal inductors?  The application would be multiband 
> dipoles.

There was an article about toroid traps in QST about 20 years ago. It made 
its way into various ARRL antenna books and the Handbook, but has not been 
popular in recent years. Regular LC traps, twintraps and coax-cable traps are 
pretty much dominant.
>  
>  Seems that now that my max QRO is 12 watts maybe designs that use toroidal 
> inductors would make sense.  Some clever mechanical considerations, w.r.t. 
> strain relief and weatherproofing, might make possible some clever designs.
>  
>  Is the reason we've never seen much along these lines because (a) it's 
hard 
> or (b) it's dumb, both being the two major reasons why you sometimes don't 
> see things that might make mathematical sense.
>  
Some reasons:

1) Heavier and bulkier than equivalent LC, twintraps or coaxcable traps. 
2) Separate capacitor needed
3) Difficult to adjust with a dipper
4) Toroid core cannot be used for mechanical purposes

For a simple LC trap, wind insulated wire on a piece of PVC plumbing pipe of 
appropriate size. Mount the capacitor inside the pipe. Holes in the pipe ends 
allow the pipe to be both coil former and strain insulator. Adjust be 
adding/removing turns or fractions of turns. 

Twintraps and coaxial cable traps have been discussed at length on the 
newsgroup rec.radio.amateur.antenna. A QST article in the December, 1984 
issue tells all about coaxcable traps, and Reg Edwards' website has lots of 
freeware on all sorts of traps and trap antennas:

http://www.g4fgq.com

73 de Jim, N2EY