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45
AVOIDING IMAGE FREQUENCIES
You might discover one of your regular stations on anoth-
er frequency that is not listed. This might be what is known
as an image frequency. For example, you might find a ser-
vice that regularly uses a frequency of 453.275 also on
474.675.
To see if it is an image, do a little math.
Note the new frequency. 474.675
Double the intermediate frequency
of 10.7 MHz (21.400) and subtract it
from the new frequency. –21.400
If the answer is the regular frequency, 453.275
then you have tuned to an image.
Occasionally you might get interference on a weak or dis-
tant channel from a strong broadcast 21.4 MHz below the
tuned frequency. This is rare, and the image signal is usu-
ally cleared whenever there is a broadcast on the actual
frequency.
20-310.fm Page 45 Wednesday, August 4, 1999 10:49 AM