The CBRS Class License: Things You Know (And Some You Might Not)
Despite the Citizen Band Radio Station class license being available on the Federal Register of Legislation for anyone to view, there remains a significant amount of folklore, here-say and downright misinformation surrounding the appropriate use of CB radio frequencies in Australia.
Things You Probably Already Knew
Maximum Allowable Power
The maximum allowable output power on UHF CB is 5W. You are permitted to use high gain antennas such as yagi or stacked dipoles to increase your EIRP, however the use of an amplifier to increase output power is not permitted. It should be noted that channels 22 and 23 also impose a limit of 8.3W max EIRP, which has been covered extensively elsewhere.
On 27Mhz HF CB, the maximum allowable PEP is 4W for AM and 12W for single side-band (SSB). Again, you are permitted to use high gain antennas to increase your signal penetration, but the use of linear amplifiers (colloquially known as “kickers”) is not permitted.
On both UHF and HF CB, a number of channels are reserved for emergency calling. Transmission on these channels are only permitted for the purpose of preserving life or property.
On UHF CB, both channels 5 (downlink) and 35 (uplink) are reserved for emergency calling, while on HF CB only channel 9 is reserved.
While the extensive number of repeaters available on the UHF CB emergency channels make it tempting to use these channels for voice communications, it is vitally important that these channels remain reserved for emergency calling. Non emergency voice traffic on these channels has the potential to interrupt emergency calls and creates fatigue for volunteer emergency monitors who listen on these channels.
Remember – keep it clear so they can hear.
In 2011, the Australian Communications and Media Authority (ACMA) signaled their intention to disallow the use of 25kHz wideband UHF CB radios in favor of newer narrowband (12.5kHz) units in order to roughly double the amount of available UHF CB channels without increasing the allocated spectrum.
Due to significant push back from the transport/logistics and agricultural industries, the ACMA reversed their decision and continue to permit the use of wideband UHF CB radios. This means that continuing to use your existing wideband radio is permitted under the class license.
Radio manufacturers and retailers, however, are no longer permitted to produce or market wideband UHF CB radios – all new UHF CB radio units will now be narrowband.
Things You Might Not Know
Whilst it is common knowledge that HF CB permits both Amplitude Modulation (AM) and Single Side Band (SSB) modes, it is less commonly known that UHF CB permits both Frequency Modulated (F3E) and Phase Modulated (G3E) emission modes.
FM and PM are very similar and are mostly interoperable, there are subtle differences in the way in which the carrier is modulated to convey information. Frequency modulation, as its name implies, modulates (changes) the frequency of the carrier in order to convey information. Phase modulation changes the phase angle of the carrier rather than its frequency – this is a somewhat indirect way of generating a frequency modulated carrier and requires some extra audio equalization to produce an acceptable result.
Traditionally, phase modulation was used as a way to avoid the complexity in generating true FM carriers in mobile and handheld equipment, however the advent of circuit miniaturization, application specific integrated circuits and the ever plummeting cost of building electronics means that phase modulation is rarely, if ever used in new UHF CB transceivers.
Use of Uplink/Downlink Frequencies for Simplex
Section 8 of the class license clearly states that “A person must not, except for the purpose of transmitting to a CB repeater station, operate a CB station on a channel mentioned in item 5 or 8 in Schedule 1 within the operational range of a CB repeater station.”
This means that the usage of uplink/downlink frequencies for simplex (non-repeater) communications when in the range of a repeater is not legal. It is therefore best practice to avoid using any duplex (repeater) frequency for any simplex communications. If you must use these frequencies, it would be pertinent to both check the UHF CB repeater map or UHF CB repeater list to see how close you are to a repeater on the channel you are intending to use, as well as requesting a radio check on the channel to check for any activity such as a verbal radio check response, or a roger beep from the repeater.
Tone Access to Repeaters
In opposition to commonly held belief, there is nothing in the class license preventing repeater operators from requiring sub-audible tones such as CTCSS/DCS for access to UHF CB repeaters. The only exception to this is that no sub-audible tones are permitted on emergency calling frequencies such as UHF 5/35.
In practice, however, requiring subaudible tones for repeater access violates the community spirit of UHF CB repeaters and is rarely, if ever implemented.
Contrary to popular belief, the use of voice encryption/scrambling on HF and UHF CB is perfectly legal, with a few notable and important exceptions:
- Voice encryption must not be used on any emergency or calling channel – this includes UHF 5/35, UHF 11, HF 9, HF 11 or HF 16.
- Voice encryption must not be used via a UHF CB repeater station.
Some CBRS users have opined that the allowance of encryption may potentially imply that the use of encrypted digital modes with FM-based carriers (such as 4FSK used by DMR) are permitted. It should be noted that this is not the case – digital modes, whether encrypted or not, use a different emissions designator (FXE) which is not permitted by the class license.
Audible tones (such as DTMF and SELCALL) are permitted on CB, so long as they occur for no more than 3 seconds in any 60 second period.
Modification of Radios & Accessories
In Section 6(d) of the act it is stated: “[A person must not] make an alteration to a CB station, or to accessory apparatus used in the operation of a CB station, that is likely to cause interference to radiocommunications”.
This section calls into question the legality of many modifications which are commonly made to 27Mhz CB radio sets in particular and is a fairly complex and nuanced legal issue.
The most common type of modifications radio operators undertake are modifications to accessories – in particular microphones. Whilst some accessories such as echo mics may be irritating to other users, they are unlikely to be captured by this section of the class license as they are not likely to cause interference to radiocommunications.
A power mic is a microphone with a built in audio preamplifier. It is designed to increase the amplitude of the audio waveform entering the AF stage of the transmitter with the intention of slightly increasing the average RF output power of the transmission. Most well engineered transceivers should limit the output power in the RF stage – either through the use of a discrete limiter or as a byproduct of the design of the RF output stage. It would, however, not be unreasonable for a radio inspector to make the argument that the use of a power mic, when coupled with a poorly designed/maintained transceiver, could theoretically cause interference to radiocommunications by either exceeding the 12W allowable PEP in the class license, or by causing spurious emissions as a result of the transmitter section being overdriven.
A clarifier is designed to allow the radio operator to slightly adjust the receive frequency of a transceiver in order to account for things such as thermal drift, doppler shift, atmospheric multipathing and other natural and man-made conditions which may cause the frequency to drift between the transmitting and receiving stations. An unlocked clarifier allows the radio operator to adjust both the transmit and receive frequencies, rather than just the receive frequency – usually by about 2kHz. As the CB band is very clearly channelized under the class license, changing the transmit frequency to be outside of the channelized frequencies outlined in the band plan is a very clear breach of the class license and therefore illegal.
While it is obvious that “freeband” modifications which are designed to allow off-the-shelf 27Mhz sets to run out of band are not permitted under the act, digital PLL modifications such as the popular CB40 may also be captured by this section of the act, even when they are configured to ahere to the band plan. It is important to note that the “likelihood” of such a modification causing interference, rather than whether the modification actually causes interference is the test under this subsection. This implies that even well-engineered products produced by hobbyists which are sold as either DIY kits or which permit the modification of firmware on the device could be considered likely to cause interference.
Additionally, many of these PLL modifications are installed for the express purpose of freebanding, meaning that a even when used within the confines of the class licence, radio inspectors are likely to be suspicious of the intention of radio operators who have fitted such a modification, further weakening the argument that the modification is compliant.
Even when intended to be used in compliance with the class licence, the likelihood of such a device causing interference is predicated on a number of factors, such as the skill of the installer, the skill of the software developer building the firmware for the device, the build quality of the device and the tolerances of the components and processes used in the manufacture of the device itself. Without a rigorous commercial production/test/verification/certification process (such as those required for type approval to receive the RCM mark), it may be difficult to argue beyond reasonable doubt that the modification in question is unlikely to cause interference. An inability to make this argument would make such a device illegal under the act.