"Dave" ) writes:
I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of other
broadcasts vying for attention.) I don't know the frequency source of all
this background noise, but would like to filter out as much of it as I can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?
TIA
Cross-posted between sci.electronics.basics and rec.radio.shortwave
Dave
It's probably designed for use with the whip, note the absence of
an antenna jack. It needs to be sensitive because it's using that
small whip, and when you add something longer, it overloads.
In other words, it's not one single signal, but all the strong local
signals, that are overloading it. TV and AM and FM broadcast stations
can put out pretty strong signals locally, and they can get around any
filtering in the radio, and still be strong, and then overload the active
stages in the receiver.
Michael