VK3YE amateur radio pages

Radio scanning

 

All material on this site (c) Peter Parker VK3YE
1997-2013.

Material may not be reproduced without permission.

 

 

Radio scanning is a recreational activity enjoyed by thousands of Australians. Scanners are special radios that receive signals not audible on standard AM/FM sets. Ambulances, police, fire services, emergency, commercial, aircraft, security, amateur and CB users were the sorts of signals available on a scanner around the clock.

Picture of an amateur handheld that doubles as as scanner

Interest in scanning peaked in the 1980s and early 1990s in the period between when stable wide-coverage VHF / UHF receivers became affordable and the rise of mobile phones and the internet. During this period many public utilities such as the police transmitted unencrypted analogue FM that all scanners received. And, before cheap mobile phones, many businesses used VHF two-way radios to communicate with their mobile staff.

Like shortwave listening, scanning is less popular than it used to be. There's less to listen to, with police (in many areas) moving to secure digital transmissions and business users using mobile phones more than the radio. Scanning appeals less to the casual listener and more users are hobbyists who may specialise in areas such as weather satellites, software defined radio or wireless computer networking.

Contrary to widespread belief, scanning is perfectly legal. However, you should not use information obtained from listening for commercial gain or criminal activity. Monitoring phone conversations on your scanner is also forbidden. Apart from that, you can pretty well scan as you please, though discretion is advised when using scanners in public. For instance, being an 'ambulance chaser' and fronting up at accident scenes, hindering emergency services is an extremely silly thing to do. Genuine scanner enthusiasts don't want to give politicians an excuse to ban or restrict the hobby, as has occurred in other countries.

Frequency allocations

The following list, though not exhaustive, gives an idea of the variety of users active on the upper HF, VHF and UHF radio spectrum.Some of the ranges given may be useful when using the scanner's 'search' feature.

H F

26.965 to 27.405 MHz  27 MHz CB radio

27.145 MHz Children's walkie-talkies

27.680 to 27.980 MHz   27 MHz marine radio (largely phased out)

28.000 to 29.700 MHz   Amateur ten metre band

29.700 to 30.000 MHz   Remote control models

V H F

30.075 to 30.300 MHz   30 MHz cordless phones (Largely phased out)

35.000 to 40.000 MHz   Two-way radio (largely phased out)

40.68 MHz  Paging systems

49 MHz approx  Baby monitors

50.000 to 54.000 MHz  Amateur six metre band

55 MHz approx  Low-cost FM walkie talkies

70.000 to 85.000 MHz   Two-way radio (VHF low band - largely phased out)

76.000 MHz approx  Ambulances

88.000 to 108.000 MHz FM broadcast band

108.000 to 137.000 MHz  Aircraft band

136.000 MHz approx  Weather satellites

144.000 to 148.000 MHz  Amateur two metre band

148.000 MHz approx  Radio paging services

148.000 to 174.000 MHz  Two-way radio (VHF high band)

152.000 MHz approx  Ethnic broadcasting services

156.025 to 156.425 MHz  VHF marine radio

156.800 MHz  Marine distress safety & calling

174.000 to 222.000 MHz  TV channels 6-11 & DAB radio

222.000 to 400.000 MHz  Defence communication

243.000 MHz  Emergency beacons (EPIRBs)

U H F

400.000 to 420.000 MHz  Two-way radio (UHF)

413.000 MHz approx  Ambulances

415.000 MHz approx  Rail

430.000 to 450.000 MHz  Amateur 70cm band

450.000 to 520.000 MHz  Two-way radio (UHF)

468 to 470 MHz approx  Police (replaced in some areas with digital transmissions)

476.425 to 477.4125 MHz  UHF CB radio

526.000 to 575.000 MHz  UHF TV channels 28 - 34

603.000 to 820.000 MHz UHF TV channels 39 - 69

820.000 to 1000.000 MHz  GSM and CDMA mobile phones

820.000 to 1000.000 MHz   Two-way radio trunking systems

820.000 to 1000.000 MHz  Spread-spectrum cordless phones

1240 to 1300 MHz   Amateur 23cm band

Notes:

1. Typical users of two-way radios include taxi companies, couriers, security personnel, factories, tradesmen, shopping centres, public transport services, local government and more.

2. GSM, CDMA and spread-spectrum communications cannot be received on normal scanners. This includes mobile and cordless phones.

3. Frequencies higher than 1300 MHz require specialised receiving equipment and antennas. Frequencies below 30 MHz are covered by shortwave receivers.

Equipment

Stand-alone 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 and/or digital radio networks. A newer, cheaper alternative, if you're listening at home, is to buy a software defined radio which plugs into a computer's USB port. While designed for broadcast radio and TV reception, those based on the RTL2832 chip can be made to tune other communication with the freely available SDR sharp (SDR#) software.

Picture of a basic scanner

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 20, preferably 50 or 100), a search function and a full-sized frequency display.Never buy a scanner offering less than this unless reception of a handful of known frequencies is all that is required.Some cheaper units do not cover the VHF airband so check that if interested in aviation listening. An under $200 model such as the Uniden UBC340CRS (pictured above) is suggested as a starter unit. An alternative, if going for your amateur licence, is to check the receive frequency range of VHF/UHF amateur transceivers. Many, such as the Yaesu VX-5R pictured at the head of this article, receive outside the amateur bands making a seperate scanner less necessary.

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 and digital transmissions.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 stand-alone 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: Same function as the similar control on a transistor radio.

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.Note that not all scanners have this feature.

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

WX: Weather button.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. Software defined receivers have all their controls adjustable via keyboard or mouse.

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. Most 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 1/4 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.

Save money by building your own scanner antennas. Performance can be every bit as good as a bought one. A really basic one that takes less than 20 minutes to build and covers VHF and UHF frequencies is the hanging dipole on this website.

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.

The main disadvantage with outside antennas is when you're using them plugged into handheld equipment. If you live in a metropolitan area, strong signals can overload the receiver and spoil reception on other frequencies. The most practical solution is to use a high-quality base station scanner. However you could also try adding an RF attenuator (to cut down the strength of received signals) or an RF bandpass filter (to make the scanner more selective).

Accessories

Frequency guide: These used to be available as books or CDs but have been replaced by the internet. The radiocommunications database on the Australian Communications and Media Authority site is a useful resource.

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 active popular frequencies (from your frequency guide) 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. Only advanced scanners can follow trunked transmissions.