Frequencies for wireless cameras, video links and microphones

How the search service works

Using the application

In the application, the microphone's place of use is selected by clicking on the map or by entering the address of the place of use in the field provided, for example, “Itämerenkatu 3, Helsinki”.

The user can also limit the frequency range to be searched, which is 470–694 MHz by default, or enter only a single frequency to be searched. The default value of 200 kHz for the channel bandwidth used by the microphone can also be changed.

After the input values have been entered, the search is started by clicking the “Search” button. The search returns the usable microphone frequencies found within the specified frequency range or only the single frequency entered by the user, provided that it is available at the selected location. If no usable frequencies matching the search criteria are found, the application displays a message to this effect.

How the application works

The usable frequencies returned by the application are frequencies that do not interfere with terrestrial television reception and are not themselves subject to interference from television transmitters currently in use. For the purposes of assessing these conditions, a minimum field strength of 45 dBµV/m caused by a television transmitter, for 50% of locations and 50% of the time, is used. The field strength is calculated in accordance with ITU-R Recommendation P.1546.

The calculation uses the maximum value of the television transmitter's effective antenna height [1]. The transmitting antenna is assumed to be omnidirectional, and the effect of bodies of water on radio-wave propagation is not taken into account. With these simplifications, the coverage area of a television transmitter forms a circle centred on the transmitting antenna. Within the circle, the field strength caused by the television transmitter exceeds 45 dBµV/m for 50% of locations and 50% of the time. Outside the circle, a radio microphone is considered neither to interfere with reception from the television transmitter concerned nor to be subject to interference from that transmitter.

In addition to television transmitters currently in use [2], the application also takes into account the regional reservations of television frequencies allocated to Finland under international agreements. At a general level, the boundaries of these geographical areas are based on Finland's regional division. There are 39 such areas at UHF frequencies, while Finland has a total of 19 regions.

As a rule, international agreements reserve more frequencies for each geographical area than are actually used for television broadcasting in that area. The application removes a television frequency reserved for an area from the usable microphone frequencies only if that frequency has already been taken into television use in the area. Otherwise, the frequency is shown in red in the list of usable microphone frequencies. This is intended to remind the user that the frequency may be taken into television use in the future.

The application takes reporter links into account

In addition to television frequencies, the application takes into account the frequencies in the 470–478 MHz and 486–494 MHz bands that are reserved nationwide for reporter links used by broadcasting companies.

Because these are individual frequencies, the bands have not been excluded in their entirety from the frequencies available for microphone use. Instead, the application excludes the channel bandwidth used by reporter links (200 kHz) around each individual frequency and additionally leaves a 100 kHz guard band relative to the microphone’s own channel bandwidth, which is 200 kHz by default.

Similarly, 100 kHz guard bands are provided next to adjacent television transmissions, which have a channel bandwidth of 8 MHz. Guard bands are also provided at the edges of the 470–694 MHz frequency band used by radio microphones in order to separate radio microphone use from other radio communications.

The application does not take other radio microphones into account

The application is intended to find radio microphone frequencies that can be taken into use immediately and that, on the basis of currently available information, can continue to be used for as long as possible.

The application does not take into account radio microphones that are already in use, because Traficom does not register them. Nor does the application take into account any intermodulation interference that radio microphones may cause to one another.

The search results returned by the application are restricted only on the basis of existing or planned television use and the frequencies reserved for reporter links used by broadcasting companies.

The frequencies suggested by the application are not the only options

Users should note that the frequencies found by the application are not the only frequencies that may be used for radio microphones. Other frequencies within the 470–694 MHz band may also be used, provided that their use does not cause interference with terrestrial television reception or with reporter links used by broadcasting companies. Such interference should not occur on the frequencies suggested by the application.

[1] In practice, the effective antenna height varies in different directions of radiation according to the elevation of the surrounding terrain.
[2] Television transmitters considered to be in use include all television transmitters listed in valid radio licences granted by Traficom.