Radio Shack PRO-29 owner manual Avoiding Image Frequencies, Frequency Conversion

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 474.675.

To see if it is an image, do a little math.
Note the new frequency.	474.675
Double the intermediate frequency of 10.8 MHz (21.600)
and subtract it from the new frequency.	–21.600
If the answer is the regular frequency,	453.075
then you have tuned to an image.

Occasionally you might get interference on a weak or distant channel from a strong broadcast 21.6 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 by 1,000:

9.62 MHz × 1000 = 9620 kHz

To convert from kHz to MHz, divide by 1,000.

2780 kHz ÷ 1000 = 2.780 MHz

To convert MHz to meters, divide 300 by the number of megahertz.

300 ÷ 7.1 MHz = 42.25 meters

36