Interference to business radio

Part of the reasoning for managing the radio spectrum is to separate users in terms of the frequency, geographical location and time of operation. This is achieved through a system of licensing. Ofcom issues licenses to individuals and creates licence exemption regulations for specific apparatus. In both instances, there are prescribed terms, provisions and limitations for lawful use.

Anyone who uses radio apparatus outside of the terms, provisions and limitations of a licence or licence exemption may be guilty of a spectrum offence.

Electromagnetic disturbances, also referred to as electromagnetic emissions, are normally considered to be unwanted emissions in the radio frequency spectrum. They can occur naturally or be generated artificially.

An electromagnetic disturbance may degrade the performance of or even stop radio communications apparatus from functioning.

Apparatus placed on the market or put into service should be designed to function compatibly within the environment in which it is intended to be used. This is called electromagnetic compatibility.

Apparatus should not emit excessive levels of electromagnetic disturbance and it should be suitably immune from external sources of electromagnetic disturbance.

If your apparatus is affected by an electromagnetic disturbance from an external source, then you need to ensure that your apparatus is suitably immune.

To protect against electromagnetic disturbances, radio receivers are reliant on adequate filtering to ensure that only the desired signal is received and unwanted transmissions or electromagnetic disturbance is rejected.

Interference may occur because of inadequate filtering or immunity from an external source of electromagnetic disturbance. In some cases, additional filters may be required to provide adequate immunity or selectivity.

The level of filtering required to reject artificial electromagnetic disturbances will often depend on the proximity of the affected receiver to the source of electromagnetic disturbance. It may not always be possible to eliminate the effect of interference by filtering alone, in which case specialist advice is recommended.

Multiple sources of electromagnetic disturbances may result in a cumulative effect. For example, the level of background levels of electromagnetic disturbance is likely to be higher in industrial areas than urban or rural areas. When planning and installing a radio system, the environment should be considered. Careful siting of the apparatus is essential to minimise the risk of interference.

In the case of artificial electromagnetic disturbances, it is important to determine if the frequency of the disturbance is within the passband of the affected receiver. If it is, physical separation may be the only option. In extreme cases, it may be necessary to relocate the affected station or apparatus to increase the physical separation from the source of electromagnetic disturbances.

Your installation should be engineered so that it complies with the terms and provisions and limitations of your licence or licence exemption.

You should take care with the type and positioning of antenna (if it is not an integral part of the apparatus). The coaxial cable and connectors should be of a suitable type for the installation and frequencies. Where an installation is co-sited with others, you can prevent problems with both the receiver performance and the transmitter spectral purity by using double-screened cable, as well as components like filters and isolators.

Interference to radio communications is considered harmful if:

• it creates danger, or risks of danger, in relation to the functioning of any service provided by means of wireless telegraphy for the purposes of navigation or otherwise for safety purposes
• it degrades, obstructs or repeatedly interrupts anything which is being broadcast or otherwise transmitted by means of wireless telegraphy and in accordance with a wireless telegraphy licence, or a grant of recognised spectrum access or otherwise lawfully.

It is unlikely that Ofcom would investigate a report of interference that is not regarded as ‘harmful’, it is not our policy and we do not have the required powers that would allow for us to do so effectively.

Congestion occurs when multiple users are operating on the same frequency or frequency band at the same time in the same area.

Where a licence is designated as ‘shared’, it will be necessary to refer to the terms, provisions and limitations of the licence. Where the problem persists contact Ofcom’s licensing team for allocation of a new frequency.

To minimise interference from other users on a shared two-way radio system, many systems employ squelch coding such as Continuous Tone-Coded Squelch System (CTCSS) or Digital-Coded Squelch (DCS). It is important to check that this is functioning and that the correct code is used.

In the case of interference experienced to licence-exempt apparatus, you can try switching channels to avoid congestion.

If your apparatus uses an antenna, you should situate the antenna away from potential sources of interference.

The FCS is a not-for-profit industry association for organisations which deliver voice and data communications solutions for business and public sector customers in the UK.

You can find guidance on reducing interference in their Code of Practice for Business Radio Site Engineering.

Where a radio station or apparatus is affected by interference and assistance is required to improve the immunity or selectivity, you should contact a reputable contractor.

Ofcom will offer you advice and assistance, either on the phone or by email. We may agree to investigate interference to business radio where we are satisfied that the interference is ‘harmful’, outside your control and all reasonable steps have been taken to minimise the effect. In addition, we may send out a spectrum engineering officer to investigate the interference. However, you may be liable for the cost of the investigation if Ofcom considers that the source is within your control.

The regulatory regime does not necessarily guarantee that interference will not arise or that enforcement action will be taken.

Before reporting interference to Ofcom, and to minimise the risk of incurring costs subject to our terms and conditions of undertaking an investigation, you should:

• keep a log of all incidents including the time date and station/apparatus affected;
• establish that the source of harmful interference is not within your control;
• ensure the affected station/apparatus is functioning correctly (e.g. installed, maintained and engineered); and
• all reasonable steps to minimise the interference have been taken.

Ofcom will not normally investigate problems caused by congestion. We may be able to help in exceptional circumstances, where the problem is widespread, affecting many individual users.

Ofcom will exercise discretion in deciding whether incidents or complaints should be investigated.

Ask Ofcom for advice and assistance or report harmful interference.

Ofcom
Spectrum Management Centre
Baldock Radio Station
Royston
Baldock
SG7 6SH

Tel: 020 7981 3131