Radio Shack 20-423 owner manual Avoiding Image Frequencies, Frequency Conversion

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462.9375–463.1875

MED

463.200–467.925

BUS

FM-TV Audio Broadcast, UHF Wide Band (470–512 MHz) (Channels 14 through 20 in 6 MHz steps)

475.750

Channel 14

481.750

Channel 15

487.750

Channel 16

493.750

Channel 17

499.750

Channel 18

505.750

Channel 19

511.750

Channel 20

Note: Some cities use the 470–512 MHz band for land/mobile service.

 

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 453.275 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 distant channel from a strong broadcast

21.4MHz above or below the tuned frequency. This is rare, and the image signal is usually cleared whenever there is a broadcast 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 MHz by 1,000:

30.62 MHz × 1000 = 30,620 kHz

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

127,800 kHz ÷ 1000 = 127.8 MHz

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

300 ÷ 50 MHz = 6 meters

Guide to the Action Bands

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Contents Channel VHF/AIR/UHF Desktop Scanner Introduction FCC Notice Scanning LegallyDual Conversion helps prevent Contents Troubleshooting SpecificationsGuide to the Action Bands Preparation Power SourcesUsing AC Power Using Vehicle Battery PowerConnecting AN Antenna Connecting the Supplied AntennaConnecting an Outdoor Antenna Look AT the Controls Understanding Your ScannerLook AT the Display Channel Storage Banks Understanding Service BANKS/BANKSService Banks AirAmateur Radio Channel Frequency MHz Marine45.880 45.900 Fire/PoliceTurning on the SCANNER/SETTING Volume and Squelch OperationStoring Known Frequencies Into Channels Finding and Storing Active Frequencies Searching the Service BanksUsing Direct Search Moving a Frequency from a Monitor Memory to a Channel Using the Monitor MemoryScanning the Stored Channels Listening to a Monitor Memory FrequencyScanning Options Turning Channel Storage Banks on and OFFMonitoring a Stored Channel Clearing a Stored ChannelListening to Weather Band Weather Channel Frequency ChartUsing the Weather Alert Listening to the Marine BankLocking Out Channels Special FeaturesUsing the Delay Function Locking OUT Channels and FrequenciesRemoving All Locked-Out Tags From Frequencies Using PriorityTurning the KEY Tone on and OFF Reviewing Locked-Out FrequenciesUsing a Computer to Program the Scanner Birdie FrequenciesUnited States Broadcast Band VHF Band Guide to the Action BandsTypical Band Usage Primary UsageBand Allocation Abbreviations ServicesAmateur Band 50-54 MHz Government Band 406-450 MHz Frequency Conversion Avoiding Image FrequenciesTroubleshooting RESETTING/INITIALIZING the ScannerResetting the Scanner Initializing the Scanner CareChannels of Operation SpecificationsNominal Limited One-Year Warranty
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