The search tool is a map-based service. The application shows frequencies available for microphones in a selected location. Such frequencies may be individual microphones' centre frequencies released from television operations or the lowest and highest centre frequencies of an available frequency band in the TV-UHF band. Make use of the service to search for frequencies available for wireless microphones within the frequency range 470–694 MHz of the terrestrial digital television.
Operating principle of the search tool
Use of the application
The location for the use of the microphone is selected in the application by clicking the map or by entering the address where the microphone is used in the field reserved for it, e.g. "Itämerenkatu 3, Helsinki".
The user can also limit the frequency band that the application searches for (the default frequency band is 470–694 MHz) or enter only one dot frequency subject to the search. In this case, the search, which is started by clicking the "Search" button, returns the operable microphone frequencies found within the entered frequency range or only the dot frequency entered by the user, as long as it can be used in the selected location. If operable frequencies matching the search conditions cannot be found, the user is notified of this in words.
Operating principles of the application
The operable frequencies that the application returns are such frequencies that do not cause interferences to normal TV reception of the terrestrial network and that are not interfered by TV transmitters in use. The criterion used for the above‐mentioned is the minimum field strength 45 dBuV/m caused by a TV transmitter (50% of the time), calculated in accordance with ITU‐R regulation P.1546. In the calculation, the maximum value [1] of the TV transmitter's effective antenna height is used for the TV transmitter, its transmitter antenna is assumed to be omnidirectional, and the impact of waterways is not taken into account in the propagation of radio waves. With the above‐mentioned simplifications, the area affected by TV transmitters is a circle. The transmitter (‐ antenna) itself is located in the centre of the circle. The field strength caused by the TV transmitter is higher than 45 dBuV/m (50% of the time) inside the circle. Outside the circle, the radio microphone is not considered to cause interferences to the reception of the TV transmitter in question and to be interfered by the TV transmitter.
In addition to the TV transmitters [2] in use, the application also takes into account the regional reservations of TV frequencies entered for Finland in international agreements. The boundaries for these geographical areas have been formed, at a rough level, on the basis of the provincial division so that the total number of the areas in UHF frequencies (470–694 MHz) is 39 when the total number of the provinces is 19. TV viewers in each area are mainly served by the main transmitter located in the middle of the area. On the average, 6 UHF frequencies have been allocated for each area. The majority of these frequency reservations are already in use, i.e. the relevant frequency has a TV transmitter or TV transmitter network serving the area. The application excludes from operable microphone frequencies the TV frequencies that have been reserved for each area only if the frequency is already in TV use in the area. Otherwise, the frequency is included in the list of operable microphone frequencies in red. The purpose of this is to remind the user that the frequency may be used for TV broadcasting in the future.
The application takes into account reporter connections
In addition to TV frequencies, the application also takes into account the frequencies that are reserved in the bands 470–478 MHz and 486–494 MHz for nationwide reporter communications of broadcasting companies. Since these are individual dot frequencies, it has been deemed appropriate not to totally exclude these bands from the available microphone frequencies. The application removes the band width (200 kHz) used by reporter communications around each dot frequency and leaves a guard band (100 kHz) that is suitable for them with regard to the microphone's own band width (200 kHz). Similarly, guard bands (100 kHz) are also left in TV emissions. The bandwidths of the emissions are 8 MHz in the UHF frequency range. In addition, guard bands are left on the edges of the frequency bands used by radio microphones in order to distinguish them from other radio communications.
Important information for the users of the application
The application is intended for the search of such radio microphone frequencies that can be brought into use immediately and the use of which can be continued, according to the current information, as long as possible.
However, the application does not take into account frequencies for the microphones that are already in microphone use because they are not registered by Traficom. Also, the application does not take into account inter‐modulation interferences which microphones may possibly cause to each other. The application limits the search results it returns only on the basis of TV use that has already been implemented or that is still being planned, as well as on the basis of the frequencies reserved for reporter connections of broadcasting companies.
The user should take into account that the frequencies found by the application are not the only frequencies that can be used for the radio microphone. It is possible to use also other frequencies allocated to microphones, as long as it does not cause interferences to the TV reception of terrestrial networks or reporter connections of broadcasting companies. Interferences like these should not occur in the frequencies that the application suggests.
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[1] In reality, the effective antenna height varies to different radiation directions as the function of the height of the surrounding ground level.
[2] TV transmitters in use include all TV transmitters that have been recorded into a valid radio license granted by Traficom.