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35

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. 

474.975

Double the intermediate frequency of 10.85 MHz (21.700)
and subtract it from the new frequency.

–21.700

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 21.7 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 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

20-508.fm  Page 35  Wednesday, August 4, 1999  1:50 PM

Summary of Contents for 20-508

Page 1: ...Cat No 20 508 OWNER S MANUAL PRO 28 30 Channel Direct Entry Programmable Scanner Please read before using this equipment 20 508 fm Page 1 Wednesday August 4 1999 1 50 PM...

Page 2: ...well as mode and status indicators 30 Programmable Channels let you store frequencies into the scan ner s memory Band Search lets you search the frequency bands for active fre quencies and direct the...

Page 3: ...compartment BNC Connector lets you connect the supplied flexible antenna or an optional outdoor antenna Audio Output Jack lets you connect optional earphones or head phones so you can listen privately...

Page 4: ...your scanner If the interference goes away your scanner is causing it Try the following methods to eliminate the interfer ence Move your scanner away from the receiver Connect your scanner to an outle...

Page 5: ...ld never in tentionally listen to These include Telephone conversations either cellular cordless or other private means of telephone signal transmission Pager transmissions Any scrambled or encrypted...

Page 6: ...d Setting Squelch 20 Storing Frequencies 21 Searching For and Storing Active Frequencies 22 Band Search 22 Direct Search 23 Search Skip Memory 24 Listening to the Monitor Memory 25 Moving a Frequency...

Page 7: ...7 Troubleshooting 36 Resetting the Scanner 37 Care and Maintenance 38 Specifications 39 20 508 fm Page 7 Wednesday August 4 1999 1 50 PM...

Page 8: ...ts you recharge nickel cadmium batteries inside the battery compartment However you must never use this circuit when you have installed non rechargeable batteries in the scanner Be sure to read Import...

Page 9: ...old or weak batteries Batteries can leak chemicals that destroy electronic circuits 5 Replace the cover If B flashes on the display and the scanner beeps every 15 seconds im mediately replace or recha...

Page 10: ...Do not use an AC adapter s polarized plug with an extension cord receptacle or other outlet unless the blades can be fully inserted to prevent blade exposure Cautions You must use an AC adapter that s...

Page 11: ...ou installed rechargeable nickel cadmium batteries in the scanner remove the plastic cap from the CHARGE jack and put the cap in the POWER jack Connect the AC adapter to the CHARGE jack This powers th...

Page 12: ...r vehicle s ciga rette lighter socket Always unplug the power cord from the vehi cle s cigarette lighter socket before you unplug it from the scanner Note The scanner receives a 12 volt input at the C...

Page 13: ...m It takes about 10 to 18 hours to recharge batteries that are fully dis charged You can operate the scanner while recharging nickel cadmium batteries but the charging time is lengthened The first tim...

Page 14: ...e antenna Your local Radio Shack store sells a variety of antennas Always use 50 ohm coaxial cable such as RG 58 or RG 8 to connect an outdoor antenna For lengths over 50 feet use RG 8 low loss dielec...

Page 15: ...o the lowest setting before you begin listening After you begin listening adjust the volume to a comfortable level Once you set the volume do not increase it Over time your ears adapt to the volume le...

Page 16: ...provide more comfortable lis tening Plug the speaker cable s 1 8 inch mini plug into your scanner s jack ATTACHING THE BELT CLIP You can attach the supplied belt clip to make your scanner easier to us...

Page 17: ...fre quency during band or direct search CLEAR erases an incorrect entry or an error Enters the decimal point in a frequency MON 0 stores frequencies into and accesses the monitor memory Enters the nu...

Page 18: ...listen to a monitor memory WX appears when you scan the preprogrammed weather channels flashes when you lock the keypad appears when batteries are low D appears when you program a channel for a two se...

Page 19: ...19 b appears during a band search d appears during a direct search H appears during a band search hold h appears during a direct search hold 20 508 fm Page 19 Wednesday August 4 1999 1 50 PM...

Page 20: ...0 channels Note The first time you turn on the scanner the channels might not have any frequencies stored in them but the scanner will con tinuously scan the empty channels 3 Press MANUAL to stop the...

Page 21: ...sitivity If reception is poor turn SQUELCH clockwise to decrease receiver sensitivity STORING FREQUENCIES Follow these steps to store frequencies into channels 1 Press MANUAL enter the channel number...

Page 22: ...nd at 0125 MHz steps Without battery or external adapter power the scanner protects the frequencies stored in memory for about 60 minutes SEARCHING FOR AND STORING ACTIVE FREQUENCIES Band Search A ban...

Page 23: ...If you tune to a search skip frequency L appears on the display See Search Skip Memory If you want to change the frequency band repeatedly press HOLD BAND The selected frequency band is displayed Dire...

Page 24: ...on the fre quency during a band or direct search The scanner stores the frequen cy in memory and resumes the search To clear a single frequency from skip memory so the scanner can stop on it during a...

Page 25: ...nto the scanner s monitor memory you can listen to it by press ing MANUAL then MON 0 MOVING A FREQUENCY FROM THE MONITOR MEMORY TO A CHANNEL Follow these steps to move a frequency stored in the monito...

Page 26: ...en a query and a reply To avoid missing a reply you can program a 2 second delay into any channel When the scanner stops on an active channel with a programmed delay it continues to monitor the channe...

Page 27: ...e lock out from all channels press MANUAL then press and hold L OUT S S until the scanner beeps twice about 3 seconds MANUALLY SELECTING A CHANNEL You can continuously monitor a single channel without...

Page 28: ...r should stop within a few seconds then you hear the local weather broadcast If the broadcast is weak you can press WX E again to scan through the rest of the weather band USING THE KEYLOCK Once you p...

Page 29: ...severe you might be able to turn SQUELCH clockwise to cut out the birdie The birdie frequencies on this unit to watch for are 31 2 MHz 41 6 MHz 52 0 MHz 145 6 MHz 156 0 MHZ To find the birdies in your...

Page 30: ...Amateur 144 00 148 00 MHz High Range 148 00 174 00 MHz UHF Band 300 00 MHz 3 0 GHz U S Government 406 00 420 00 MHz 70 cm Amateur 420 00 450 00 MHz Low Range 450 00 470 00 MHz FM TV Audio Broadcast Wi...

Page 31: ...atrol CB Citizens Band CCA Common Carrier CSB Conventional Systems CTSB Conventional Trunked Systems FIRE Fire Department HAM Amateur Ham Radio GOVT Federal Government GMR General Mobile Radio GTR Gen...

Page 32: ...nd 29 7 50 MHz in 5 kHz steps 29 900 30 550 GOVT MIL 30 580 31 980 IND PUB 32 000 32 990 GOVT MIL 33 020 33 980 BUS IND PUB 34 010 34 990 GOVT MIL 35 020 35 980 BUS PUB IND TELM 36 000 36 230 GOVT MIL...

Page 33: ...7 740 BUS 157 770 158 100 TELB 158 130 158 460 BUS IND OIL TELM UTIL 158 490 158 700 TELB 158 730 159 465 POL PUB ROAD 159 480 OIL 159 495 161 565 TRAN 161 580 OIL 161 600 162 000 MARI RTV 162 0125 16...

Page 34: ...PUB 454 000 OIL 454 025 454 975 TELB 455 050 455 925 RTV 457 525 457 600 BUS 458 025 458 175 MED 460 0125 460 6375 FIRE POL PUB 460 650 462 175 BUS 462 1875 462 450 BUS IND 462 4625 462 525 IND OIL TE...

Page 35: ...onally 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...

Page 36: ...AC or DC outlet Recharge the recharge able batteries or replace the non rechargeable batteries The optional AC or DC power adapter is not connected Be sure the adapter is fully inserted into the DC 12...

Page 37: ...eys turn on the scan ner PROBLEM POSSIBLE CAUSE REMEDY Keypad does not work The keylock function is activated Press KEYLOCK until dis appears from the display to turn off the keylock flashes on the di...

Page 38: ...t which can cause premature wear of parts Handle the scanner gently and carefully Dropping it can damage circuit boards and cases and can cause the scanner to work improperly Use only fresh batteries...

Page 39: ...MHz and 450 kHz Squelch Sensitivity Threshold Less than 0 4 mV Tight S N N 25 dB Built in Speaker 19 16 inches 4 cm 8 Ohm 0 5 W Dynamic Type Power Requirement DC 4 AA Batteries 6 0 VDC or 4 AA Recharg...

Page 40: ...ing the warranty period take the product and the Radio Shack sales receipt as proof of purchase date to any Radio Shack store Radio Shack will at its option unless otherwise provided by law a correct...

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