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UK CB specifications.The following specifications refer to the MPT1382 standard. This applies to equipment placed on the market after 1997. Equipment designed to the previous standard, MPT1320, may still be used and does not need to be changed in any way. This is not intended as a complete statement of the requirements, only a general plain English guide with as little technical babble as possible. Combination equipment.
Citizens Band equipment may be combined with other receiving equipment, such
as car audio systems. However, it must not be possible to transmit while any receiver
is operational.
Note:
This would make it legal to have both broadcast and CB receivers going at the same
time, as long as the broadcast receiver was shut off when the CB part transmits.
Frequencies.
Equipment may cover either the UK band (27.60125 - 27.99125MHz), the European
band (26.965 - 27.405MHz) or both.Note:
The conversion of single band CB equipment to dual band is not allowed.
Modulation.
Only Angle Modulation may be used. This includes Frequency Modulation (FM) and
Phase Modulation (PM). All other forms of modulation are prohibited.Frequency deviation.
The maximum deviation is ± 2KHz.
Note:
For old equipment, placed on the market before 1997, the maximum deviation
was 2.5KHz. Such equipment may still be used.
Carrier power.
The maximum allowed RF output power is 4 Watts. For equipment with an integral
antenna, this is the maximum ERP. Otherwise, it is the maximum transmitter
output.
Note:
ERP is the Effective Radiated Power of the whole system, including for antenna
gain. As hand-held antennas have a gain of less than unity, it may be legal for
a hand-held CB to put more than 4 Watts into the antenna, as long as the
effective radiated power is still within the permitted 4 Watts maximum.
Adjacent channel power.
The maximum allowed adjacent channel power is 20 microwatts.
Note:
This is the average power you transmit on the channel above and below the one you
are using. Increasing deviation will increase adjacent channel power, possibly
causing interference to other users.
External audio input connections.
The equipment may not have connections to allow for external audio input to the
transmitter, other than a microphone and selective calling.External connections are allowed for devices which do not modulate the transmitter, such as a speech synthesizer (talkback) to give audible channel indication. It must not be possible to transmit the audio output of such devices. Frequency tolerance.
The equipment must operate within ± 0.6 kHz of stated channel frequencies.Frequency synthesis.
Where a Phase Locked Loop (PLL) is used to generate frequencies, the transmitter
must be disabled whenever the loop is not locked.
Note:
All modern CB equipment uses PLL systems. When you change channel or switch from
receive to transmit, the PLL has to change the frequency. All systems take a finite
time to do this, and the loop is only locked once it has done this job.
Some early UK CBs did not disable the transmitter while locking the PLL, and they generate what can only be described as a humongous fart sound which could be heard on other frequencies. Clearly, this kind of equipment had to be stopped from being sold. Maximum usable sensitivity.
Where equipment may be used with an external antenna, the maximum receiver sensitivity
is 6 dBµV.Adjacent channel selectivity.
Equipment with provision for an external antenna must have a minimum of 60dB adjacent
channel attenuation.
Note:
This did not apply to equipment placed on the market before 1997. Such equipment
may still be used, but may suffer more interference from other CB users. Fitting a
crystal filter may bring old equipment up to the new standard.
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