Radio Shack PRO-79 owner manual Avoiding Image Frequencies

Page 40

To turn on the keylock, hold down for about 3 seconds un-

til the scanner beeps three times and appears. To turn it

off, hold down for about 3 seconds until the scanner beeps

three times and disappears.

AVOIDING IMAGE FREQUENCIES

You might discover one of your regular stations on another fre- quency 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 MHz.

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 transmission 21.4 MHz above or below the tuned frequency. This is rare, and the image signal is usually cleared whenever there is a transmission on the actual frequen- cy.

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Contents PRO-79 Channel VHF/Air/UHF Handheld Scanner Features Page FCC Notice Frequency Types of Transmissions Range MHzScanning Legally Contents Special Features Installing Batteries PreparationUsing AC Power Using Vehicle Battery PowerCharging Rechargeable Batteries Connecting AN Antenna Connecting the Supplied AntennaConnecting an Outdoor Antenna Connecting AN Earphone Headphones Listening SafelyConnecting AN Extension Speaker Traffic SafetyUnderstanding Your Scanner Look AT the KeypadNumber KeysLook AT the Display AIRDLY Understanding Banks Channel Storage BanksService Banks Fire/PoliceAmateur Radio AirMarine Channel Frequency MHz 156.9250 Monitor Memories RESETTING/INITIALIZING the Scanner OperationResetting the Scanner Initializing the ScannerStoring Known Frequencies Into Channels Searching the Service Banks Finding and Storing Active FrequenciesUsing Direct Search Page Listening to a Monitor Memory Using Monitor MemoryMoving a Frequency from a Monitor Memory to a Channel Scanning the Stored Channels Turning CHANNEL-STORAGE Banks OFF and on Monitoring a Stored ChannelListening to the Marine Bank Clearing a Stored ChannelListening to the Weather Band WX Alert Special Features DelayLocking OUT Channels or Frequencies Locking Out ChannelsReviewing Locked-Out Frequencies Locking Out FrequenciesRemoving Lockouts From All Frequencies Using Priority Removing Lockouts From All Frequencies in All Service BanksUsing the KEY Lock Using the Display BacklightTurning the KEY Tone on and OFF Avoiding Image Frequencies General Guide to Scanning Guide to FrequenciesNational Weather Frequencies Birdie FrequenciesTypical Band Usage MHz Guide to the Action BandsPrimary Usage Abbreviations Services Band AllocationMeter Amateur Band 50-54 MHz Aircraft Band 108-136 MHzGovernment Band 137-144 MHz Meter Amateur Band 144-148 MHzVHF High Band 148-174 MHz Centimeter Amateur Band 420-450 MHzFrequency Conversion Low Band 450-470 MHzTroubleshooting Squelch is notCare and Maintenance Specifications Volts DC, 4 AA Batteries Page Division of Tandy Corporation RadioShackFort Worth, Texas
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