Why Is My Old European TV Sound Buzzing? 5.5 MHz #Filte #sound #pal

An old European television could show a perfectly good picture in Britain but have missing, distorted or buzzing sound because it used a different analogue TV sound standard. In this video, I show a 5.5 MHz ceramic sound filter and explain how we used to convert suitable European televisions for British reception. On many sets, this involved replacing the sound filters with 6 MHz versions and adjusting the sound circuit’s ferrite cores to get the clearest sound. Depending on the television, other changes were needed, and sometimes a slight background buzz remained. Although both sets could use PAL colour, that did not mean their aerial sound systems were compatible. The same problem could affect imported video recorders receiving British terrestrial television or feeding a television through their aerial output. The technical explanation: Your photograph shows a three-legged component marked SFE 5.5 MC, consistent with a 5.5 MHz ceramic sound IF filter. “MC” is the older notation for megacycles per second—the same unit now written as MHz. The crucial distinction is that PAL describes the colour encoding; B/G and I describe the associated transmission standards. Much of continental Europe used PAL B/G, whereas British 625-line analogue television used PAL I. Analogue system Sound carrier above picture carrier B/G, used across much of continental Europe 5.5 MHz I, used in Britain Approximately 6 MHz D/K, used in some other countries 6.5 MHz M, associated with American NTSC broadcasts These figures are the spacing between the picture and sound carriers, rather than the frequency of the television channel itself. In an intercarrier receiver, the picture and sound carriers produce a difference signal. For British reception, that difference is approximately 6 MHz. The sound filter selects this signal, and the FM sound detector extracts the audio. A circuit designed around 5.5 MHz cannot correctly process a 6 MHz signal without suitable changes. The ferrite adjusters you remember were probably the tuned sound IF or discriminator coils. Their exact purpose depended on the chassis. Adjusting them brought the tuned circuits into alignment with the new sound frequency; on some sets, capacitors, sound traps or the main IF filtering also needed attention. Why did countries choose different frequencies? They adopted different television transmission standards, with different picture bandwidths and channel arrangements, before colour television became established. B/G provided approximately 5 MHz of picture bandwidth; British System I provided approximately 5.5 MHz, with the sound carrier correspondingly farther away. Both could later carry PAL colour while retaining their existing transmission arrangements. Even though System G and System I both used 8 MHz channels, their internal allocation differed. Why could some buzz remain after conversion? Replacing the ceramic filter did not necessarily correct the response of the whole receiver. If the remaining circuitry weakened the sound carrier or allowed picture-related interference into the sound detector, some buzz could persist. This is known as intercarrier buzz. It can change with picture content, particularly strong contrast, lettering or patterns. BBC research documented both picture-generated interference and receiver overloading as causes. A properly converted set could give clean sound; residual buzz was not inevitable, and buzzing alone does not prove a standards mismatch. How this applied to video recorders: A video recorder had two relevant sections: its tuner, receiving programmes through the aerial, and its RF modulator, producing an aerial signal for the television. Both needed the appropriate standard. The VHS tape itself did not store the broadcast’s 5.5 or 6 MHz sound carrier. The recorder extracted the audio before recording it. Consequently, a compatible PAL recording could play correctly through separate audio/video connections, such as SCART, while giving sound trouble through an incompatible RF output. The equipment you remember was generally called multisystem or multistandard. Support for different sound standards, VHF/UHF channels and PAL/SECAM/NTSC playback varied by model; these were separate capabilities, as was its mains-voltage rating. 4.5 MHzPlease Like and Subscribe ‪@chrisconquerDIY‬