Selcall

A 5-tone sequence ( also called selective ) is used for selective addressing of individual wireless devices ( Private Call ) or a whole group (group ), especially in analog BOS radio. But in other radio services will use this technique.

Requirements

In order to perform the alarm, requires the radio, according to its desired function as a transmitter or receiver, the following modules:

  • Pointcast donor
  • Multicast transmitter
  • Pointcast evaluator
  • Multi-party evaluator

The triggering of the alarm is by the device itself, or another accessory.

Function and application

If a stored reputation, ie stored in the device 5-tone sequence received, the possibilities of the reaction are varied:

  • Collective: it opens only the speaker
  • Group call: as collective, in addition unique sounds a ringing tone
  • Selective call: as group call, the ringing tone is repeated several times, call lamp

In bad radio the Technical Directive BOS prescribes precise reactions of the receiver; so in addition to an acoustic and a visual and tactile signaling is prescribed by a vibrating alert.

In more complex wireless networks, the number of the caller can also be transferred to another 5-tone sequence. It is then shown on the display of the called party. This is not supported by all devices.

Modern devices can transmit with the 5-tone sequence stored in the device status as texts. Similar to the FMS of the BOS, but the text can be freely selected.

Other applications for 5-tone sequence:

  • Simple remote control, such as pump on / off, controlled by the elevated water tank
  • Relay opening, and thus use only by Authorized
  • Speech item request from the control center. Speakers and Button are otherwise locked
  • STUN / UNSTUN to disable stolen radios
  • Emergency call, such as taxi radio transmits its identifier and 30 sec language the passenger compartment
  • Silent query: control center may ask device to send

Coding

The coding of 5-tone sequences based on the national standards. Modern devices (which are to be successful around the world ) can choose between ten different standards and another user -defined standard switch. In Germany it is the ZVEI standard. In other countries, CCIR, EEA, EIA, Natel used. The different frequencies of the individual tones ZVEI are:

A typical sequence consists of five digits, five different tones together, all of which have a defined duration of 70 ms. To increase the security alarm, is (for example, 88) sent not twice the 2000 - Hz tone in the repetition of a digit. Instead, the second tone of the original is (2000 Hz ) is replaced by the Alternativton (R, 2600 Hz) to ensure the distinctness of successive tones.

BOS application

The 5 -tone call is normally used in analog BOS radio to alert emergency personnel. Another, also common expression for the 5-tone sequence is the term loop. 5-tone sequences can personal, location- based, vehicle- bound or oriented will be awarded to a desired Ausrückstärke. If a pager receives its assigned sequence, the alarm is triggered. Also sirens can be triggered by 5-tone sequences, but there is still a transmitted after the 5-tone signal dual ( superposition of two tones each having a different frequency, but the same volume level ) is necessary. Under current legislation, the tone sequence to be sent twice. To guarantee a higher alerting security, twice two tone sequences can be sent. In BOS radio additionally certain times for the sustain and tolerances for both audio frequency and duration must be adhered to, which are recorded in the TR -BOS.

In an analog radio network alerting as well as the announcement is usually on the same channel at the 4- meter band is done. In digital alarm response of the radio message receiver and the transmission of data bits in the 2- m band is done. The digital equivalent of the 5-tone sequence is the Radio Identification Code ( RIC short ).

The disadvantage of the analogue alarm signal falls on the critical viewing of the alarm duration. A single alarm will take at least 2.5 seconds to be connected in a subsequent announcement, according to the guidelines at least five second pause and the duration of the actual spoken message. Should it be necessary to alert several loops, the total duration of alarms increased significantly.

Another disadvantage is the security against eavesdropping. The analog BOS BOS radio network, in which this type of alarm is applied is encoded in the rarest of cases, and thus it is not a problem, listen to the radio network. Willful false alarms can also be generated by a wireless device.

The dual tones for siren control consist of the following frequency pairs:

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