Advantages of 405 lines?

[Andy Green]

Originally Posted by Hybrid tellies

Another advantage of 405 was its narrower bandwidth. This meant that as the BBC continued with 405 after WW2 they expanded their network during the 1950's just using the 5 band 1 channels. If they had restarted using 625 (if this was possible) they would have required the extra channels in band 3 as you can only fit 3 625 line channels in band1. Of course this would have meant the new ITV service would have had to start on the uhf bands which would have been a daunting challenge back in the mid 1950's.
So that means that most of our European neighbours, who did start on 625, only had one national tv station using both vhf bands, it was not until the mid 1960's that they were able to open a second network on the uhf bands, whilst here in the UK, thanks to 405, we were well ahead with our two national networks up and running by the early 1960's using the vhf bands!

Well, here in Ireland, they originally used mainly band III, with a couple of high power band I Tx's(they had some low power band I relays) for 625 lines. They also duplicated the service on the same bands in the North and East of the country on 405 lines. This was phased out to facilitate the second RTE TV channel, which also used band III in most areas.
By the 70's they also switched on a coupleof high powered UHF transmitters, but even today, two system I (wider than continental systems) 625 line services exist predominantly on band III (band 1 is no longer used).
So with careful planning, I expect they could have had BBc and ITV on 625 lines, it may have stretched the TV tuner technology in 1955, but by 1960 I'd say it could have been done.

[murphyv310]

Hi.
On the aspect of recording onto video using 405 the overall results are much superior with the VCR not requiring the chroma circuitary required for 625 PAL.
The two photos were recordede today using a sony C7 beta machine and you can see the ghost effect caused by the Drop out compensator and also the excellent definition, on test card F there is noticeable Chroma Crawl from my NTSC 405 line source, I would think owing to the good bandwidth from a VCR on 405 that no chroma processing would be required hence machines would have been simpler and cheaper. I will check though to see if it does work on the Decca 405 colour project set the next time I dig it out of the loft (Phew) .
Regards.
Trevor