On Apr 27, 10:59*pm, Paul Keinanen wrote:
On Mon, 27 Apr 2009 16:34:23 -0700 (PDT), K7ITM wrote:
If you have very sensitive earphones (and sensitive ears!) and a good
antenna, what may matter more than keeping the loss down to an
absolute minimum is getting rid of interfering signals. *A single-
tuned circuit with 10kHz -3dB bandwidth offers only 20dB attenuation
of a signal 50kHz away, and a signal 200kHz away is attenuated only
about 32dB (assuming I didn't mess up my mental arithmetic). *That's
not a lot if you live in a metropolitan area with several stations
nearby, and you want to hear the ones from far away. *You can make the
tuner with two or even three tuned circuits that are properly coupled,
and get much better attenuation of those unwanted signals. *But more
tuned circuits means more loss in the tuner, too, even if you use high
Q coils.

Unless you live very near an international SW broadcasters, how do you
expect to get any usable amplitude modulated signal in the middle of
the SW band for your crystal set ?

To make the situation even worse, the power delivered by a matched
dipole at 10 MHz is only 1/100 (-20 dB) of the power delivered by a
matched dipole on 1 MHz due to the antenna capture area.

Paul OH3LWR

Actually, I was thinking in the paragraph you quoted more of MW
broadcast, but since you mention SW: I have it on good authority that
European SW broadcasters put 7MHz signals into the East coast of the
US at levels up to close to 0dBm into a receiver's antenna terminals
when the skip is right. That's using an antenna with a bit of gain
over a dipole, but nothing fantastic. (That level gave me a goal for
strong-signal handling for an HF receiver I recently put into
production.)

Cheers,
Tom