5TVO stands for 5 tone and is a combination of 5 tones sent after one and other and sound's like this.
This is known as ZVEI or Selcall. Selcall is an abbreviation for Selective Calling. Your radio will have a microprocessor in it or Integrated Circuit that will generate audio tones at within a certain time period, normally being around 30 to 40ms. The receiving radio would also be equipped with similar equipment that decodes the tones. Both the transmitter and receiver radio will have a number programmed into it so it triggers an alert to the operator when a certain number is received. By using this method, one can 'selectively call' a friend without saying a word.
With the now coming availability of Condor 16 and Condor 3000 radio's for Radio Amateur use, there is a demand for division on this use in the Dutch Radio Amateur community.
The advantage for use of such a system can be comprehensive. You can always' be reachable with a transceiver in code lock. If someone gives your number the transceiver will let you know and give acknowledgment on the same frequency or on an other. Besides the use of a transceiver there is also the use of a bieber for this purpose.