"Dave" wrote
...
On Mar 20, 8:26 am, Szczepan Białek wrote:
"Phil Allison"
...
"Richard Clark"
Now, as to your experience of receiving signals on the wrong
frequency, that is a classic situation of image rejection being poor
due to the lack of a tuned front-end (something that dissappeared with
the dinosaurs). If I were to guess on the basis of 40 year old
experience fixing these suckers, your off-frequency signals are
probably shifted by twice the IF frequency of your receiver. The
classical FM IF frequency of 10.7 MHz might apply, but time has
marched on and designers may select their own. This old standard
would argue that you shouldn't experience images except where they
would be out-of-band (the 88-107 band with this IF would force that).
** Hearing the same FM station at more than one spot is still possible
even with a 10.7 MHz IF frequency - if the signal is very strong. The
reason is harmonics of the incoming carrier generated in the RF stage
interacting with harmonics of the local oscillator in the mixer.
It sound like the "Luxembourg Effect". The signal was from the dipole
antenna.
Are now the FM stations which use the dipoles?
Eg:
A 100MHz FM carrier generates a harmonic at 200MHz in the receiver.
When the local oscillator is adjusted to 94.65 MHz, its second harmonic
is
189.3 MHz.
The difference frequency is then 10.7 MHz - so goes through to the FM
detector.
In this situation, the FM deviation is doubled so the recovered audio
will
be distorted on loud passages.
all antennas are dipoles, you just can't always see the other half.
If I can't see the other half it is the monopole.
So I repeat my question: Are now the FM stations which use the dipoles?
and Luxembourg has nothing to do with it, your silly frequency
doubling notions should be packaged up in art's box and never see the
light of day.
The dipoles have the directional pattern like this:
http://www-antenna.ee.titech.ac.jp/~...ole/index.html
It looks like the interference of the many sources (dipoles have the two).
The two sources not in phase double the frequencies.
S*