Jim Brown On Tuesday, March 03, 2009 at 4:34 PM, Jim Brown wrote.
> On Tue, 3 Mar 2009 01:53:19 -0000, Geoffrey Mackenzie-Kennedy wrote: > >>Yes, I take your point. It is the fine tweaking of phase that I find >>easier >>to do with a capacitor!! > > Please tell me how you would do that with this antenna! :) The > "tweaking" > involved requires nothing more than looking at my measured data and > winding the > choke to put the resonance where you want it. It isn't very "tweaky" -- > the Q > of a choke like this is around 0.5. The inductance of the coil formed by the outer braid of the coax feeder in the L-C traps that I used is less than that of a choke, and when space wound and tuned to resonance by the trap's capacitor the Q of this tuned circuit is quite high, but not high enough to compromise the operating bandwidth of the driven elements on 40m. I am not absolutely certain as to why a small change in the resonant frequency of the traps in a two element vertical array affects their phasing, albeit slightly. SWR measurements taken on the individual elements did show a small change in their drive point impedances as one of the trap's resonant frequency was changed by a small amount, which would affect the phasing between elements of course. Unfortunately I had to change from using vertical arrays on 40m to horizontal arrays, in some directions our large oak and beech appeared to distort the radiation pattern of the verticals. 73, Geoff GM4ESD ______________________________________________________________ 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
