UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 13th May 2018, 7:19 pm   #1
radio10
Retired Dormant Member
 
Join Date: Sep 2014
Location: Trincity, Trinidad and Tobago, West Indes
Posts: 3
Default TV system differences?

How did the vintage 405 Marconi system differ from the later analogue 625 PAL and today's digital system in general?
radio10 is offline  
Old 13th May 2018, 9:54 pm   #2
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
Default Re: TV system differences?

Have a read of this Wikipedia article, answers some of your questions.

https://en.m.wikipedia.org/wiki/Broa...vision_systems
__________________
Frank
Nuvistor is online now  
Old 13th May 2018, 10:00 pm   #3
Cobaltblue
Moderator
 
Cobaltblue's Avatar
 
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,823
Default Re: TV system differences?

Hi well that's a pretty big question with so many elements.

You could do worse than starting here.

https://en.wikipedia.org/wiki/405-li...evision_system

Also PAL refers to the method of encoding colour information, there are other standards for this such as NTSC.

There are also other line standards.

See here:

https://en.wikipedia.org/wiki/Broadc...vision_systems

Crossed with Frank

Cheers

Mike T
__________________
Invisible airwaves crackle with life or at least they used to
Mike T BVWS member.
www.cossor.co.uk

Last edited by Cobaltblue; 13th May 2018 at 10:01 pm. Reason: Crossed.
Cobaltblue is online now  
Old 13th May 2018, 10:06 pm   #4
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: TV system differences?

If you check the specs on the video signal itself, the main difference is the line rate which in the 625 system requires a 15.625 kHz line (horizontal) oscillator and in the 405 requires a 10.125kHz oscillator. The horizontal flyback time I think is a littlle longer in the 405 system too. The field rate is the same in both cases at 50Hz, so the vertical oscillator in the TV is the same, but there are some differences with equalizing pulses in the vertical sync block of the video signal with 625 system to improve the interlace.

Because of that different timing though, and the the way the line scanning current builds up with time, converting a set or making a set with dual horizontal scanning frequencies is not as simple as just altering the line oscillator frequency, the width & linearity have to be corrected as well.

On the other hand American 525 line , 60Hz field rate monochrome TV sets are easy to convert to 625 line/50 Hz sets as often the H osc will just pull into range and the vertical oscillator timing capacitor is easily reduced in value. (These are also FM sound sets with the same modulation system and 4.5MHz sound easily reset to anywhere between 5 & 6 MHz)

Also in the 405 system, the modulation of the transmitted video carriers was such that the sync reduced the carrier level. Opposite to the system later used in 625 line sets and in America. Also in the era of the 405 line system, the video carrier 45 MHz was transmitted 3.5 MHz above the sound carrier on 41.5Mhz, later the video carrier was transmitted on higher range VHF frequencies and 5, 5.5 or 6 MHz below the sound carrier depending on the country. And of course in the 625 system , by then, the sound was FM not AM too.

It is possible to make a vintage 405 line TV run on the modern 625 system (now obsolete) the steps that are required:

1) modifiy the line osc an line deflection circuit for 625 operation (Surprisingly this is relatively easy with sets with self oscillating line output stages, by increasing the core gap in the Lopty) In other sets the H oscillator is changed and the width & linearity compensated for with various methods.

2) Reverse the video detector diode

3) replace the audio detector with a discriminator or Ratio detector

4) Re-tune the RF circuits for a wider gap, say 46MHz video and 40.5MHz sound, if the sound-vision difference was say 5.5 MHz, I think its 6MHz UK , its 5.5 in NZ & AU.

5) add a VHF turret tuner to the front end (connect it to the antenna input) to down-convert the higher VHF channel frequencies (This also flips the vision carrier above the sound carrier)

I did this with a vintage 405 line set in NZ and it worked very well on the 625 line system there.

And thats just for monochrome TV.

As for digital TV, that's a whole other story.
Argus25 is offline  
Old 13th May 2018, 10:10 pm   #5
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: TV system differences?

Digital systems are completely different. The details vary, but generally speaking a number of different bitstreams are multiplexed together and transmitted on a single frequency. The digital TV or digibox decodes the multiplex to extract the desired signal, and then processes the bitstream to produce video and audio according to the standard in use. Digital TVs and digiboxes are essentially computers.
paulsherwin is online now  
Old 13th May 2018, 11:14 pm   #6
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: TV system differences?

.. sorry should have said the vertical timing capacitor is easily increased, in value to get a 60 Hz field rate set to run at 50Hz, but many cases it comes in on the vertical hold control anyway when a USA made set is used in the UK or AU. Also an interesting bit of information, the American line rate was initially 15.750 KHz, but when color (NTSC) came it was slightly reduced to 15.734 kHz, and the vertical rate increased a fraction above 60Hz I think, but existing monochrome sets in the USA locked to these small changes ok.
Argus25 is offline  
Old 13th May 2018, 11:17 pm   #7
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
Default Re: TV system differences?

29.97 Hz vertical rate, NTSC 525 line system.
__________________
Frank
Nuvistor is online now  
Old 14th May 2018, 12:48 am   #8
Graham G3ZVT
Dekatron
 
Graham G3ZVT's Avatar
 
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,676
Default Re: TV system differences?

Another thing about 405 vs 625 in the United Kingdom, is all the 405 transmitters operated at VHF and all the 625 transmitters were on UHF, so when the 405 line system was eventually switched off in 1985, the VHF allocations were not re-engineered for 625 as you might have expected, VHF was abandoned as far as TV was concerned.

Unlike NTSC in the USA , PAL does not define the 625 line monochrome signal. As transmitted in the UK, it should be referred to by its CCIR designation letter I. 405 lines was system A (naturally).

Colour was never transmitted on 405/VHF apart from a few BBC engineering tests, not intended for public consumption, and I think they were NTSC rather than PAL
__________________
--
Graham.
G3ZVT
Graham G3ZVT is online now  
Old 14th May 2018, 2:49 am   #9
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: TV system differences?

Quote:
Originally Posted by rambo1152 View Post
Another thing about 405 vs 625 in the United Kingdom, is all the 405 transmitters operated at VHF and all the 625 transmitters were on UHF, so when the 405 line system was eventually switched off in 1985, the VHF allocations were not re-engineered for 625 as you might have expected, VHF was abandoned as far as TV was concerned.
I didn't know that. So UK made 625 line TV's would not have had VHF tuners in them. All the early NZ ones did and UHF came later. Surprisingly NZ was still running VHF & UHF TV analog when I was last there some months ago. Analog TV transmissions have been gone in AU for some time.
Argus25 is offline  
Old 14th May 2018, 2:51 am   #10
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: TV system differences?

Quote:
Originally Posted by Nuvistor View Post
29.97 Hz vertical rate, NTSC 525 line system.
Making the vertical osc frequency or field rate just under 60Hz, rather than just above as I suggested in post #6.
Argus25 is offline  
Old 14th May 2018, 3:42 am   #11
winston_1
Hexode
 
Join Date: Oct 2012
Location: London, UK.
Posts: 497
Default Re: TV system differences?

Quote:
Originally Posted by Argus25 View Post
I didn't know that. So UK made 625 line TV's would not have had VHF tuners in them.
Sadly that was usually the case. Problem was some areas had cabled systems with 625 at VHF (Stevenage was one), and blocks of flats were often like this as well. I had an argument with Philips over this when I wanted a set for such a situation. Didn't help though and I had to source a set from a continental manufacturer. Towards the end of the analogue era manufacturers, including Philips, started fitting all band tuners and still do to this day (except Panasonic).
winston_1 is offline  
Old 14th May 2018, 6:13 am   #12
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: TV system differences?

The original post didn't ask about converting a set, or say in which direction.

The 405 line TV system was a monochrome system introduced in the UK in 1936. 50 fields per second with a half line offset creating 25 frames per second as the fields interlace together. This was an anti-flicker measure. Of the 405 lines, 377 are in the visible picture, the remainder are blanked in the retrace periods. The line frequency is 10.125 kHz.

405 signals were transmitted with positive modulation (white gives max transmitter output, sync gives mimimum) AM. All UK 405 transmitters were on VHF channels. Accompanying sound was transmitted as AM, offset 3.5 MHz above the vision carrier.

625 line PAL is not so easy, it covers a group of standards. Different countries chose different bandwidths and sound offsets, and radio frequency bands. All were colour. Sound standards varied. The standards were indicated by a suffix letter like PAL-I.

The 625 monochrome system introduced in the UK used negative modulation (peak transmitter power on the sync pulse) AM, and the sound was FM. These signals were only broadcast on the new UHF channels in the UK. The 50 fields/25 frames only remained. Line frequency became 15.625kHz

PAL colour signals were designed to be compatible with the monochrome ones, so monochrome TVs would give a monochrome rendition. PAL was derived from the earlier American NTSC system with several improvements, some of them quite complex. To understand PAL, it's easiest to study NTSC first so you can see why some things were done.

If you just want to understand the two systems, there is plenty of reading and wikipedia is a reasonable starting point. If you are aiming to convert signals, or convert a set, you have to decide on which 625 PAL standard.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 14th May 2018, 7:51 am   #13
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
Default Re: TV system differences?

Given that the OP lives in Trinidad and Tobago, I wonder if he is enquiring about the legacy systems used there rather than in the UK?
__________________
Graham. Forum Moderator

Reach for your meter before you reach for your soldering iron.
Station X is offline  
Old 14th May 2018, 8:18 am   #14
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: TV system differences?

It may be PAL-M

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 14th May 2018, 9:04 am   #15
Radio1950
Hexode
 
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
Default Re: TV system differences?

Quote:
Originally Posted by radio10 View Post
How did the vintage 405 Marconi system differ from the later analogue 625 PAL and today's digital system in general?
The main difference is that 625 line TV, and digital, is that they were "watchable".

The UK 405 programs I saw were absolutely dreadful.
Radio1950 is offline  
Old 14th May 2018, 9:35 am   #16
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: TV system differences?

Do you mean that UK 405 productions looked bad on the Australian system? That's because they would have been 16mm telerecordings. The 405 system gave very good results on the 405 TVs of the day. It was abandoned for reasons of standardisation within Europe, not because it performed poorly.
paulsherwin is online now  
Old 14th May 2018, 9:43 am   #17
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: TV system differences?

405 line compared to 626 = not good, hence body filler attempts like spot wobble.

Not to mention the budgie killer line whistle

Lawrence.
ms660 is offline  
Old 14th May 2018, 10:09 am   #18
kan_turk
Hexode
 
kan_turk's Avatar
 
Join Date: Mar 2014
Location: Dublin, Ireland
Posts: 396
Default Re: TV system differences?

Quote:
Originally Posted by winston_1 View Post
Sadly that was usually the case. Problem was some areas had cabled systems with 625 at VHF (Stevenage was one), and blocks of flats were often like this as well. I had an argument with Philips over this when I wanted a set for such a situation. Didn't help though and I had to source a set from a continental manufacturer. Towards the end of the analogue era manufacturers, including Philips, started fitting all band tuners and still do to this day (except Panasonic).
Very interesting, and very strange given that Philips were marketing standard all-band and VHF/UHF equipped sets in Ireland from the 60s onwards - what era are we talking about?

Rgds
John
kan_turk is offline  
Old 14th May 2018, 10:31 am   #19
peter_scott
Dekatron
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
Default Re: TV system differences?

Another minor difference between 405 and 625 is that transmissions of the former were very largely vertically polarised whereas the latter were very largely horizontal. I say very largely because some of the smaller local stations broke the general rule.

Peter
peter_scott is offline  
Old 14th May 2018, 12:11 pm   #20
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: TV system differences?

UK dual standard TV sets had both VHF and UHF tuners in them, along with the need for two antennae (usually opposite polarisations) and downleads.

There was no point in a VHF tuner in a 625 line single standard set. There were no suitable transmissions.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:38 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.