SCANNER F.A.Q.

Welcome to the Grove Frequently Asked Questions page. We hope this will bring you a better understanding of scanners and what those confusing terms mean.

Choosing the right scanner:

     One of the most common questions we receive here is "Which scanner is best?" Like asking, "Which car is best?" there are many considerations.

    For example, do you want a hand-held, desktop or mobile scanner? Do you need high memory-channel capacity? Would you like wide frequency coverage for UHF military aircraft or commercial FM and TV broadcasting? Do you have trunking in your area? Is cost a consideration?

Hand-held or desktop?

    Don't worry about sacrificing performance when you buy a hand-held scanner; they have the same sensitivity, selectivity and dynamic range as their desktop/mobile counterparts. Their speakers are smaller, so audio quality and volume may be compromised. You can always plug in an external speaker, and attaching an outdoor antenna will give you the same coverage as it would with a comparable desktop.

    When you're using the battery-operated scanner indoors, it is a good idea to plug in the AC charger/adaptor. While it won't charge the batteries as fast when the scanner is operating as it would when it's off, it will prevent the batteries from becoming discharged during indoor use.

    Although an 8-10 hour recharge time is normal, don't worry about overcharging nicads; memory is a myth of the past. Unless the batteries get overly warm, temporary reduction in capacity ("voltage depression") is restored after one or two discharge cycles. The newer NiMH (nickel metal hydride) batteries are even better. Batteries should last at least three years with proper care.

Are some scanners better than others?

    Generally speaking, you get what you pay for. The least expensive scanners may have just as good sensitivity and selectivity as the higher prices units, but may have poorer dynamic range (overload more easily), reduced memory-channel capacity, small frequency coverage, lack of trunk tracking, and no digital reception.

    The consumer electronics marketplace bulges with products competing for your dollar. By following a few simple rules you make the right choice in buying that new scanner. At the present time, programmable scanners are manufactured by Uniden, Icom, AOR, Radio Shack, Yaesu, and Alinco. 
    Most popular scanners have excellent sensitivity and reasonable selectivity, but suffer from intermodulation and image interference from strong signal overload, especially when used with an outdoor antenna.

Frequency Range:

    The most common frequency ranges monitored by scanner enthusiasts are 30-50 MHz (VHF low band), 144-174 MHz (VHF high band), 406-512 MHz (UHF) and 806-960 MHz. By law, all scanners must exclude the cellular telephone frequencies.

    The civilian VHF aircraft band (118-137 MHz, AM mode) provides another interesting target for monitoring, and some scanners also include the military UHF aircraft band (225-400 MHz, AM mode).
    The prospective scanner buyer should decide which listening targets are of greatest interest before purchasing a radio.

Mobile, Base, or Handheld?

    Scanners come in a variety of models to meet the particular needs of the listener. Do a lot of driving? Install a mobile unit. Constantly in and out of the car, office or home? You may prefer a hand-held. Do most of your listening in the office or home? A base unit would be more practical, and most mobile units can become base units with an AC power adaptor.
    An AC wall adaptor also operates hand-held scanners to save battery power, and usually charges batteries as well.
    Most hand-held scanners have small speakers which do not compete well in a noisy environment; an earphone or external speaker will solve that problem.    

Frequency Conversion- The tuning range of a radio can be expressed in frequency (kHz or MHz) or in wavelength (meters).  There is a simple relationship:

1 MHz (1 million hertz)=1,000 kHz. (kilohertz); thus, 9.620 MHz= 9620 kHz.

 To convert MHz to meters, or meters to MHz, simply divide 300 by either one; thus, 30 MHz = 10 Meters, and 40 meters = 7.5 MHz.

Digital scanning- All modern scanners are digital -- that is, they all have microprocessors. But the term more commonly refers to the signal that it is receiving. If the voice has been "digitized," it cannot be heard on an ordinary scanner. While most digitization is used for privacy, and is unlawful to decode, there is one digital system -- APCO Project 25 ("P25") -- that can be legally monitored, at least in its lowest digital level. Many scanners now include this digital mode.

Terminology and Specifications

CTCSS: Continuous Tone Coded Squelch System (CTCSS, sometimes called “PL” for Motorola’s “Private  Line” trademark) is a method of including a low-pitched tone in the transmission which trips the squelch on the intended recipient’s receiver(s), thus excluding the undesired signals from other users sharing the frequency. Some scanners now include the CTCSS capability so the listener can choose which service to monitor on a multi-user frequency. 

Dynamic Range is the ability of a scanner to handle extremely strong as well as extremely weak signals without distortion or overloading. Since most scanners do this poorly, this specification is virtually never given.

Intermodulation ("intermod') is produced in the scanner circuitry when strong signal frequencies mix together, producing spurious signals on seemingly-unrelated frequencies. It is often recognized by its distorted sound, often containing mixed audio from multiple signals. Intermod is a consequence of inadequate dynamic range.

Images are produced in every receiver. They are recognizable as a duplicate of the legitimate signal, typically offset by 21.4, 21.6, or 21.7 MHz (twice the intermediate frequency--I.F.) from the actual frequency, depending upon the scanner. With up-conversion design, image frequencies may fall outside the tuning range where they aren't a problem.

Memory: The ability of a scanner to store favorite frequencies for scanning.

S.A.M.E. (Specific Area Message Encoding) Weather Alert: Your National Weather Service will alert you of weather and other emergencies for your county if programmed.

Scanning: The rapid sampling of memory-stored frequencies to find active frequencies. When the transmission ends, the scanning cycle resumes until another active frequency is found.

Searching: An automatic sweep between an upper and a lower frequency limit in a search for activity. When an active frequency is found, the search stops until the activity ends, then resumes.

Selectivity: The radio's ability to reject adjacent frequency interference; the sharper, the better, especially in strong-signal conditions. Average selectivity for a scanner is typically 30 kHz (+/- 15 kHz) at -50 dB.

Sensitivity: The weakest signal voltage that the radio will respond to audibly; the lower the number, the better. Good sensitivity is about 0.3-0.5 microvolts.

Priority Channel: Assigning a specific memory channel to be automatically sampled every few seconds for activity regardless of other functions currently running on the scanner.

Trunking: The automatic, equal sharing by several departments of a pool of frequencies. These frequencies often change between transmissions as the number of users increase or decrease.

VFO Control: A variable tuning control to allow continuous manual tuning up and down in frequency found on some scanners.

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