Burst signal
In communications engineering , especially in television technology , and electrical measurement technology, a burst signal is a limited number of oscillations of a fixed frequency ; so it has a certain, fixed duration. In contrast to a continuous sinusoidal signal, which has only one frequency component , the bandwidth of a burst signal is greater, the shorter the burst is. Burst signals are used for test purposes or for the time-limited transmission of the information on the phase position and the frequency of an oscillation .
Burst is derived from this and is also used in data transmission protocols in which a short data packet is sent at fixed regular intervals. Such a packet, possibly already modulated onto a carrier, is called a burst , depending on the protocol nomenclature . Digital Enhanced Cordless Telecommunications (DECT) is an example . Due to the modulation, the above information on the spectrum no longer applies without restriction.
Applications
PAL burst
In the field of analog television technology such as PAL , a burst signal is used to transmit the correct phase position and frequency of the color carrier from the transmitter to the television receiver. The television needs an uninterrupted version of exactly this oscillation in order to be able to display a color picture; with the help of this information he can generate it himself so that the correct demodulation of the color information can take place. The adjacent figure shows an oscillogram of the so-called color burst of a PAL signal, which is transmitted immediately after the line synchronization pulse (the signal edge to the left of the oscillation packet). In this case, this burst of approx. 2.3 µs represents the transmitter's color subcarrier with a frequency of 4.43361875 MHz. The entire oscillogram shows about 8% of a complete video line with 5 µs; the visible part of the video line begins to the right of the part shown; the height of the baseline on which the vibration packet sits corresponds to the black level of the video image.
Multiburst
In measurement technology , burst signals are generated with special test generators. A sequence of burst signals of different frequencies is known as a multi-burst signal and enables the frequency response or bandwidth of a transmission channel to be easily estimated . The transmitted signal is viewed with an oscilloscope .
A multi-burst signal is also part of many television test patterns . In the middle of the figure, to the left of the orange rectangle, vertical lines that become narrower from left to right can be seen. A video frequency corresponds to each line spacing; the lines usually represent frequency packages of 1, 2 and 3 MHz, the orange field corresponds to the color carrier frequency of approx. 4.43 MHz. A weakening of the respective frequency is noticeable through the low contrast of the lines. A similar system for determining bandwidth in television and video technology is the frequency broom .
Measurements on loudspeakers
Burst signals can also be used for measurements on loudspeakers . This technique has the advantage that reflections on walls only hit the measurement microphone after the burst and, in contrast to measurements with continuous sinusoidal signals, no anechoic space is required.
literature
- Keith Jack: Video Demystified, A Handbook for the Digital Engineer . 3. Edition. LLH Technology Publishing, 2001, ISBN 1-878707-56-6 .
- LF multiburst generator . In: Funkschau special issue . No. 34 , 1982, ISSN 0172-2778 , pp. 13-15 .