Avoiding Image Frequencies; Frequency Conversion - Radio Shack PRO-66 Owner's Manual

20-511.fm Page 35 Wednesday, August 4, 1999 2:13 PM

AVOIDING IMAGE FREQUENCIES

You might discover one of your regular stations on another frequency
that is not listed. It might be what is known as an image frequency. For
example, you might find a service that regularly uses a frequency of
453.075 also on 474.775.
To see if it is an image, do a little math.
Note the new frequency.
Double the intermediate frequency of 10.85 MHz (21.700)
and subtract it from the new frequency.
If the answer is the regular frequency,
then you have tuned to an image.
Occasionally, you might get interference on a weak or distant channel
from a strong broadcast 21.7 MHz below the tuned frequency. This is
rare, and the image signal is usually cleared whenever there is a broad-
cast on the actual frequency.

FREQUENCY CONVERSION

The tuning location of a station can be expressed in frequency (kHz or
MHz) or in wavelength (meters). The following information can help you
make the necessary conversions.
1 MHz (million) = 1,000 kHz (thousand)
To convert MHz to kHz, multiply the number of megahertz by 1,000:
9.62 (MHz) x 1000 = 9620 kHz
To convert from kHz to MHz, divide the number of kilohertz by 1,000:
2780 (kHz)
To convert MHz to meters, divide 300 by the number of megahertz:
300
1000 = 2.780 MHz
7.1 MHz = 42.25 meters
474.775
–21.700
453.075
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