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,

-Alex


Basically it's due to bad design. All radios have an IF that reduces all
incoming signals to a single frequency that then is used for audio
output. If you're hearing an internally produced harmonic, then it
usually means that your radio is suffering from a design flaw, or that
there's some bad parts. Considering how cheaply these Chinese radios are
made, it's not surprising that some would have such poor design and/or
build quality that internal harmonics or "birdies" would be all over the
place. If your radio can't properly handle the IF, then it follows that
SW signals will have images too. Such a radio is practically useless for
DX.


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