Scanners come in handheld, in-car or home station configurations.  Most tune several frequency segments between 25 and 1300 MHz.   The more expensive units have fewer gaps in received frequencies, provide more memory channels, and offer the ability to track transmissions from trunked radio networks. 

 It is suggested that beginners start with a fairly basic scanner.  Though it might not cover as many frequencies as a larger unit, they are easy to use and can provide hours of listening enjoyment.  The main things to look for in a scanner are sufficient memory channels (at least 50) and a search function.  Never buy a scanner offering less than this unless reception of a handful of known frequencies is all that is required.  Models such as the Uniden Bearcat 120XLT (handheld) or 248XLT (home unit) are good starter units. 

 More sophisticated scanners cover more frequencies and have more memory channels.   Other features offered include a tuning knob, selectable channel steps and ability to track trunked transmissions (see later).  The greater frequency coverage allows reception of a wider range of signals that cannot be received on cheaper units.  More memory channels is always an advantage, particularly for users in major cities.   Better scanners (particularly those built for home use) also have improved rejection of strong nearby signals.  Strong signal rejection is an issue on cheaper handheld units that can overload if connected to a home station antenna in urban areas.  A typical example of a high-end scanner suitable for home and car is the Uniden 780XLT.  

A scanner has a few more controls than a normal AM/FM radio.  The following explains their function.  Note that there are some variations between brands and models. 

      ·        Off/on/volume:  Self-explanatory.

·        Squelch/Mute:  Silences the receiver in the absence of a signal or when scanning.  Set this control to the point where the noise just stops. 

·        Manual:  Makes the scanner ready to accept a frequency keyed in by the user. 

·        Numerical keypad:  Allows frequencies to be keyed in manually.  Also useful for setting search limits and other functions, depending on the scanner. 

·        E: Enter button.  Press this after keying in a frequency.

·        Scan: Allows the set to automatically tune through stored frequencies (memory channels).  When a channel is busy the scanner will stop.  Scanning will resume when activity ceases. 

·        Limit: Allows operator to set lower and upper frequency limits of a search (see below). 

·        Search: Pressing this causes the scanner to tune across every channel between pre-set lower and upper limits.  Searching is useful when you only know the approximate frequency of something you wish to listen to. 

·        VFO:  Allows manual tuning across a range of frequencies, much like an ordinary AM/FM broadcast receiver.  On some scanners the same control may be used for other functions, such as selecting preset memory channels. 

·        Hold:  Prevents scanning from resuming, even if activity has ceased. 

·        WX: Weather.  In North America pressing this allows reception of a weather information service.  This button has no useful function in Australia. 

Some scanners have additional buttons missing from the above list.  Others use a menu system so that a large number of functions can be selected from a small number of controls on the front panel.  With any scanner, the user should master the basic skills of entering a frequency, storing memories, scanning and searching. 

 Antennas

 The short whip antenna supplied with handheld and base station units is adequate for local reception (between 5 and 30km).   However a better antenna increases the receiving range and variety of signals heard, especially from radio users not operating via repeater stations.  

 Fitting a longer whip to a handheld scanner can improve reception, particularly at lower frequencies.  Roof-mounted mobile antennas are a good idea if using a handheld scanner in a vehicle.  Handheld scanners use a standard BNC connector and suitable mobile scanner antennas and mounts are widely available.  Mounting is similar to UHF CB antennas, but less critical unless long-distance reception is required. 

 If listening at home, an antenna mounted outside is required for best reception.  If even performance in all directions over a wide range of frequencies is required, a discone antenna is a good choice.  A discone is able to receive signals up to 20-100 kilometres away.  Longer reception ranges are possible if using yagi or log-periodic beam antennas.  As these are directional antennas, a rotator is required.  Beams are particularly recommended for listeners in urban fringe or rural areas where signals are weaker. 

 It is suggested that those only interested in tuning a narrow range of frequencies obtain an antenna for this range rather than use a broadband antenna such as a discone.  This is because the narrow band antenna may have gain over the discone and provide better reception.   Mobile or base station antennas made for transmitting can be particularly useful here.  For instance a 27 MHz CB base station antenna will provide good reception between 26 and 30 MHz.   An antenna designed for UHF CB will do well thirty megahertz either side of 477 MHz.  A 5/8 wavelength whip made for 144 MHz will cover VHF high-band two-way radio signals, and possibly the aircraft band as well.  If a shorter antenna is required, a ¼ wave whip cut for 160 MHz will provide reception on both VHF high-band (144-174 MHz) as well as UHF frequencies around 480 MHz.

 The best antenna in the world can be let down if poor antenna cable is used.  Thin feedline can lose half to three-quarters of the signal before it reaches the scanner!  Cable loss gets worse with increasing frequency and is particularly serious above 400 MHz.   If most listening is in the VHF range, and cable lengths are kept to ten metres or less, RG58 cable will suffice.  On the other hand, if the cable run is much longer, or your main interests are in the 400, 500 or 900 MHz bands, a thicker cable such as RG213 is preferred.

Accessories

 ·         Frequency guide.   A frequency book is the scanner user's most useful companion.  It is particularly useful for the newcomer who wants some 'sure-fire' frequencies to start off with, and/or wishes to listen to a particular user.   Books vary widely in content some are simple lists of frequencies, while others have more detailed information by region.   Frequency books are available from suppliers such as Dick Smith Electronics and Tandy.  Radiomag carries frequency lists and articles on scanning; look for it at newsagents each month. 

·        External speaker.  Can provide better sound than the scanner's inbuilt speaker.  One with a 3.5mm plug will suit nearly all scanners.

·        Carry case.  Offers protection for handheld scanners. 

  Using a scanner

 With any scanner, the user should master the basic skills of entering a frequency, storing memories, scanning and searching.  These procedures are explained in the instruction book that comes with the scanner.  Because some functions are not self-explanatory, secondhand scanners without instruction books should be avoided.

 Start by entering a few popular frequencies as memories and press scan.  With any luck the radio will scan through the channels, stopping when one is busy.  Next experiment with using the 'hold' button.  Also try searching between two limits.  The frequency range chosen should be one known to be active the above frequency table or a scanner frequency book will assist here.

 After several sessions of listening, write down your favourite frequencies, and divide them into groups such as fire, ambulance, amateur, CB, etc.  Enter these under separate 'banks' in the scanner's memory.  By using the 'scan banks' feature on most scanners, the user can choose what they want to hear by simply selecting which bank(s) they wish to scan. 

 What is 'trunking'?

 Trunking is an advanced communications system where the frequencies of multiple users are co-ordinated through a central control channel.  This is done automatically without the need for the radio user to change frequencies.  Trunking is used in all states, but particularly in NSW, ACT and Tasmania. 

 Only advanced scanners can follow trunked transmissions. 

This article was republished with permission for P.Parker

Peters web site is http://www.alphalink.com.au/~parkerp/radio.htm