Available online
Description
The programme demonstrates how phase errors are minimised in the PAL system. The operation of a PAL decoder is demonstrated by displaying relevant photographs.
The programme demonstrates how phase errors are minimised in the PAL system. The operation of a PAL decoder is demonstrated by displaying relevant photographs.
| Module code and title: | T321, Telecommunication systems |
|---|---|
| Item code: | T321; 16 |
| First transmission date: | 02-10-1976 |
| Published: | 1976 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:22:25 |
| + Show more... | |
| Producer: | David Saunders |
| Contributors: | David Crecraft; Gaby Smol |
| Publisher: | BBC Open University |
| Keyword(s): | Colour decoder; PAL (Phase Alternation by Line); PAL colour television system; Saturation errors; Waveforms |
| Footage description: | Smol, using an oscilloscope display of the r.f. spectrum of a t.v. signal, introduces the programme. He points out the various components of the signal. Smol uses an animated phasor diagram to explain the principles of the PAL system. He goes on, using this diagram, to explain how PAL deals with phase distortion. Smol demonstrates the way in which phase distortion affects both the NTSC and PAL systems. (PAL changes hue errors to saturation errors which are much less noticeable.) Smol, with a block diagram of a colour receiver, explains in detail how the PAL colour decoder operates. David Crecraft uses an oscilloscope to display signals used when decoding PAL colour. He points out the various components of the trace. Crecraft next shows and discusses photographs of expanded traces from the oscilloscope. He begins with two photos of the trace of an incoming chrominance signal. Crecraft next looks at and discusses photograph of traces for the adder and subtractor. Smol, with a T.V. receiver block diagram, explains how these signals are demodulated. Crecraft displays the signal waveforms in receivers for a burst gate input pulse and then the output signal from a burst gate. Crecraft goes on to show photographs of waveforms for two lines in the receiver and transmitter of the reference oscillators. He points out that they are 90 degrees out of phase in both cases. Crecraft uses an oscilloscope and photographs to display three waveforms at once for the receiver reference oscillator, the U reference (modulator input) and the V reference (demodulator input). Smol sums up. |
| Master spool number: | 6HT/72173 |
| Production number: | 00525_5235 |
| Videofinder number: | 1357 |
| Available to public: | no |
