Hi, Jim. I had thought about that concept years ago when I was doing more casual QRP portable operation (camping, Flight of the Bumblebee-type stuff, etc), but I never tried it because I just assumed that the impedance at the end of a "dipole" (i.e., where the choke would be on the coax) was so high that you wouldn't get much decoupling at that point. Have you been able to verify that a simple choke really blocks the shield current there? Or am I misunderstanding something?
73, Dave AB7E Jim Brown wrote: > On Mon, 2 Mar 2009 10:16:27 -0800, Randy Cook wrote: > > >> HOW MANY OF YOU ARE USING PAR ELECTRONICS END FEDS >> > > This is a VERY easy antenna to build. Why would anyone want to buy > what they can build in an hour for a fraction of the cost? See > > http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf > > One half of the dipole is a quarter-wavelength of wire, connected to > the center conductor of the coax feedline. One quarter-wave from the > end where the wire is connected you add a ferrite choke that > functions as an "end insulator" for the coax, which makes the > section of the coax between the wire and the choke the other half of > the dipole. You do NOT apply a velocity factor when determining the > length of the coax between the wire and the choke. > > If you're running 100W or less, the choke can be as simple as 10 > turns of the coax around two 2.4-inch o.d. toroids, #31 or #43! I > used much bigger chokes to run 1.5kW. For 20W or less, a single > toroid is plenty. > > 73, > > Jim Brown K9YC > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
