Re: Directional ferrite? - FARMERIK
--- In ultralightdx@..., kevin asato wrote:
> That would be your null.
> If there are particular stations/frequencies you want to remove from your reception, maybe a wave trap will be what is needed. Do a search on crystal or xtal radios. Those guys have done a lot of work on reception techniques to increase selectivity and reduce (not necessarily eliminate) unwanted stations from their bare bones radios to enhance their DX capabilities. (Of course we would all like to live in a dream location like Mike Tuggle (Hawaii) where almost every station you hear is DX!).
Even without the DX, Hawaii would be okay! A wave trap (a resonant circuit that blocks signals) would work swell with an external antenna. Here, instead of a top-mounted ferrite-rod antenna, I think I'd favor John Bryant's mod, that adds a coupling loop to the internal antenna, connected to a mini jack. It's in the Files section. The internal antenna would be essentially replaced by a system comprised of a tuned external antenna and wave trap. It would be hard to get a wave trap working with an antenna tuned by the radio.
But -- if you installed John's mod and built a good-sized tunable air loop, 2-feet or more on a side, it might null those pests well enough by itself, and you wouldn't need a wave trap. If you're interested in wave traps, I recommend http://theradioboard.com/rb/index.php It has a search engine. Searching the "Crystal Radios" forum for "wavetrap OR wave AND trap" I found 34 threads! Friendly group, just watch out they don't lure you into building crystal sets. Nan may bake you into a pumpkin bread. :)