--- In ultralightdx@..., kevin asato <kc6pob@> 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
<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. :)

73,

Jim, KR1S
http://qrp.kearman.com/ <http://qrp.kearman.com/>