+++++++++++++++++ From: N2EY at aol.com Date: Sun, 17 Nov 2002 07:58:44 EST Subject: Re: [Elecraft] Trap designs with toroidal inductors To: Mike at crv.com, elecraft at mailman.qth.net In a message dated 11/16/02 10:36:50 PM Eastern Standard Time, Mike at 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 +++++++++++++++++ Date: Sun, 17 Nov 2002 10:34:57 -0500 From: "Mike Zak" To: Subject: [Elecraft] Trap designs with toroidal inductors Thanks to all for the various responses to my question on the use of = toroidal inductors for trap designs. The pointers provided by members of the list led me to a section of the = 1986 ARRL handbook (page 33-6) that summarizes work that W1FB did on the = subject. The article answers the questions I had. Mike - W1MU ++++++++++++++++ Date: Sun, 17 Nov 2002 11:21:25 -0700 From: "James R. Duffey" To: Subject: [Elecraft] Re: Elecraft digest, Vol 1 #344 - 30 msgs Mike - Doug DeMaw published some information on using toroids for antenna traps in the June 1983 QST. It has been republished in the ARRL book "QRP Classics", page 180. Toroid based traps will have high Q and hence narrow bandwidth. I hope that this helps. - Dr. Megacycle KK6MC. -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++ From: "Stuart Rohre" To: "Mike Zak" , Subject: Re: [Elecraft] Trap designs with toroidal inductors Date: Mon, 18 Nov 2002 15:00:12 -0600 Well Mike, Another reason besides the mechanical complexity of mounting the fragile cores in a trap configuration outdoors and weather proofing it, is the fact you might in an antenna want to spread out the inductor for three reasons. 1) High Q for lowest loss. 2) A solenoid coil does not bring the high voltage ends close to each other like a toroid might. 3) It is more than an inductor, and you might as well let the solenoid length add to the radiation of the antenna, and not self shield the inductor as the toroid tends to do. Thus, the solenoid trap can add to the length of radiator. Most solenoid coil traps either incorporate the capacitor inside the coil, or use coax for distributed inductance and capacitance, or use a weather shield over the coil as part of the capacitor. Although that shields the trap from radiating, it does provide a better weather resistance if done right. Note though, that those metal can traps have plastic end boots that fail from sun effects over time. 73, Stuart K5KVH +++++++++++++++