UHF Channel 22 & 23 – A Clarification
Recently there has been some discussion on various radio groups surrounding the appropriate use of UHF CB channels 22 and 23. Some confusion surrounding the rules surrounding these channels has ensued during the course of these disucssions. This article will provide clarification surrounding the appropriate usage of these channels.
Channels 22 and 23 remain the only designated wideband channels still present under the 80 channel UHF CB narrowbanding – this is due to the fact that telemetry and telecommand data often requires a wider spectral channel to achieve the modulation required to carry data. It should be noted however that any carrier on these channels should not exceed 16kHz as was the case with the previous wideband UHF CB class licence – this is to ensure that appropriate guard bands are present to prevent bleed-over into channels 21 and 25.
The legislation surrounding the use of these channels is quite clear – Section 6(h) of the Radiocommunications (Citizens Band Radio Stations) Class Licence 2015 states “A person must not: operate a CB station to transmit speech on channels 22 (476.950 MHz) or 23 (476.975 MHz)”. No voice transmissions of any kind, are permitted on either of these channels.
In addition to this, there are a number of other restrictions which apply to these two channels. Unlike voice channels which have the usual 5W transmitter power limitation, channels 22 and 23 also have a limitation of 8.3W EIRP under the class license. This means that antenna gain must also be accounted for when using these channels – this may require artificial limiting of the output power of the transmitter or the use of a lower gain to ensure the EIRP limit is not exceeded.
Additionally, the transmitter must not operate in a duty cycle of more than 10 seconds in any 60 minute period – this means that no more than 10 seconds of transmission are permitted in any given one hour period. The transmitter must also be equipped with a time out timer which shuts down (powers off) the transmitter should it continuously transmit for more than three (3) continuous minutes.
Whilst it may be tempting to use these channels to run packet data services such as AX.25/APRS, the ACMA website regarding the usage of CB radio is clear that no packet data or other types of data services are permitted on these channels.
A few users have opined that digital voice modes (such as P25 or DMR) could be used on these channels – it is noted that the UHF CB class license only permits analog FM (F3E) or PM (G3E) emissions modes on UHF CB – this specifically precludes the use of digital voice modes on any UHF CB frequency. Additionally, digital mode capable radios must comply with AS/NZS 4365:2011 (Radiocommunications equipment used in the UHF citizen band radio service) which specifies the types of modulation (F3E/G3E) permitted by equipment operating on these frequencies. Programming a digital capable UHF radio with CB frequencies, even if that radio is type approved, is still a breach of the Radiocommunications Act, as digital modes are not permitted as per the class license.
What is it used for then?
While the restrictions on the usage of channel 22 and 23 may seem punitive and arbitrary, these channels form an important part of the secondary usage of the UHF CB service. If you’re in a metro/suburban area, it’s likely that you’ve never heard any legitimate activity on these channels.
These channels are designated for telemetry and telecommand and are especially useful in regional areas where agricultural operations are common. These channels are often used for tone control of devices such as gates, water pumps, bore/tank level meters and perimeter alarms. This allows farmers and other landholders to remotely control these devices without having to physically attend to them – massively reducing the amount of travel required around these often extensive homesteads.
The Future of UHF CB Telecommand/Telemetry
Whilst telecommand/telemetry has been an important tool in combating the tyranny of distance in large agricultural operations, the importance of this technology is slowly diminishing as the cost and complexity of higher bandwidth, feature rich devices such as 900Mhz/2.4Ghz/5Ghz Ethernet radios, satellite telemetry networks and sensor mesh networks continues to plummet. Low power sensor networks based on digital technologies such as Zigbee, LoRAWAN and even LTE NB-IoT are rapidly eroding the marketshare of traditional UHF CB telecommand devices.
As these new devices continue to replace traditional tone-based monitoring devices, the ACMA may seek to re-farm channels 22 and 23 for another purpose – however until that time comes, it is important to ensure that the rules of the class license are respected.