27-08-2020, 08:16 AM
A note on using VHS machines to record 405.
A basic VHS machine knows nothing of the video signal at line rate. The luminance is simply modulated on to a carrier (FM) and laid down on slanting tracks. One track for each field. There's a disturbance between fields as one track ends and new one starts. This can often be seen at the bottom of the screen. The only circuit that knows about line rate is the dropout compensator. This stores a line of video in a delay line which repalces the current line if the signal from the tape is poor. The DOC will make a mess of 405 reply if the tape has many dropouts. Fortunately VHS tapes are usually pretty good.
Many later VHS machines have more complex signal processing which may mangle a 405 signal. The only way to find out is to try it.
Why did people record 405 on VHS machines? After 405 shutdown in 1985 the only people who had 405 signals available were a very few who had acquired ex-BBC or ITV converters. Alternatively you could point a 405 camera at a 625 monitor. EIther way, there was no convenient source of 405 signals for vintage sets. Hence the circulation of 405 line VHS tapes. With the availability of compact standards converters the need for recording 405 went away. I have written about all this in several artcicles which are on my website.
With the excellent Aurora and Hedghog converters readily available, providing 405 line signals for your vintage TVs is very easy.
A basic VHS machine knows nothing of the video signal at line rate. The luminance is simply modulated on to a carrier (FM) and laid down on slanting tracks. One track for each field. There's a disturbance between fields as one track ends and new one starts. This can often be seen at the bottom of the screen. The only circuit that knows about line rate is the dropout compensator. This stores a line of video in a delay line which repalces the current line if the signal from the tape is poor. The DOC will make a mess of 405 reply if the tape has many dropouts. Fortunately VHS tapes are usually pretty good.
Many later VHS machines have more complex signal processing which may mangle a 405 signal. The only way to find out is to try it.
Why did people record 405 on VHS machines? After 405 shutdown in 1985 the only people who had 405 signals available were a very few who had acquired ex-BBC or ITV converters. Alternatively you could point a 405 camera at a 625 monitor. EIther way, there was no convenient source of 405 signals for vintage sets. Hence the circulation of 405 line VHS tapes. With the availability of compact standards converters the need for recording 405 went away. I have written about all this in several artcicles which are on my website.
With the excellent Aurora and Hedghog converters readily available, providing 405 line signals for your vintage TVs is very easy.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
