That third link is especially good. The second link appears to be a part of
the third link.
Anyway, it gives a good graphical representation of the signals that appear
at the output of a mixer. Once this is visualized, it makes it easier to
understand what is happening. Thanks for the links!

Pete

wrote in message
oups.com...
Alexander Kozik wrote:

Hi all,

Radio: Tecsun P230. Problem with AM reception (spurious signal?).
There is a strong AM station 50 kW with frequency 1530 kHz within 10
miles.
Tecsun P230 detects this station when it is tuned to 620 kHz.
No other radio detects this station at 620 kHz.
Actually, other radios detect weak distant stations at this frequency.
Obviously, there is something with heterodyne 1530 - 455*2 = 620

Could you explain what is wrong with radio or just point to the
useful web pages that describe the physical/electrical background
of this phenomena. Probably, I am not interested how to fix the
problem,
I just want to understand why it happens.

Thanks a lot in advance,
--------------------------------
Simplest answer, your radio converts the incoming RF signal
down to a lowr freqeuncy for improved selectivity. In your
radio this is 455KHz.
See: http://en.wikipedia.org/wiki/Image_response
See:http://www.radio-electronics.com/info/receivers/image_response/image.php
The http://www.radio-electronics.co.uk/info/receivers/ is a prettt
good place for beginers to start learning some of the terms
and concepts in radio reception.

Terry