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4th Mar 2009, 4:51 pm | #1 |
Dekatron
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Subjective difference between 405 & 819
Hello.
I have been running all the sets this afternoon in lieu of the state visit from Geordieland of "Fernseh" to Scotland. One thing though is I have noticed how little difference is seen between the 405 line sets and the 819 line Philips (the set on the floor). The Philips is a 21 inch as is the Murphy V320A above it. No doubt the roll of of bandwidth on 819 lines makes the picture a little flat, whereas 405 can easily sustain its 3mhz bandwidth. Cheers Trevor
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4th Mar 2009, 4:53 pm | #2 |
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Re: Subjective difference between 405 & 819
another couple
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4th Mar 2009, 7:24 pm | #3 |
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Re: Subjective difference between 405 & 819
Trevor, are you up-converting to 819 from a 625 source?
If so, wouldn't this limit the 819 bandwidth performance slightly anyway?.. ie. you'd get no more definition than that possible from 625. Steve
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5th Mar 2009, 11:47 am | #4 |
Tetrode
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Re: Subjective difference between 405 & 819
Fascinating! In fact the black and white episodes of Steptoe & Son were shot on 405 I think. 9mhz of video bandwidth going through valve IF strips doesn’t do the video a great deal of good. The 405 pics are proof the system wasn’t that bad. Makes you wonder if we could have stuck with it but added an extra signal below the vision carrier to add some extra definition, at bit like PAL Plus.
Cheers Tim
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405 line TV, 1936- 1985 2007.........to the present day |
5th Mar 2009, 11:58 am | #5 |
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Re: Subjective difference between 405 & 819
I'll bang my own drum here and suggest looking at my article 405-MAC: A New Approach to Compatible HD-TV published in Television in 1988. You can read it online at my website. Go to publications and scroll down to almost the bottom of the page.
819 was a bit ahead of its time with a lot of kit struggling to do justice to the bandwidth. But then looking even further back 405 was ahead of its time too, it's just that technology caught up well before the system went obsolete. A minor pleasure of 819 was that the line whistle was inaudible to most humans. |
8th Mar 2009, 2:23 pm | #6 |
Tetrode
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Re: Subjective difference between 405 & 819
Yes I remember reading this article during my apprenticship and getting very excited, then I noticed it was the April issue!
My thoughts for "helping" the vertical definition was along the lines (no pun intended) of the Extended PAL system the Beeb came up with. Extending the whole channel bandwidth to the same as PAL I of 8mhz, so there is room for an extra 3Mhz subcarrier below the main vision carrier. Channels would overlap like the French 819 system, but on UHF EBU channel designations could stil be used.The studio camera scans 810 lines with 2 tubes (2 luminance tubes for colour), the second tube 1 line shifted so scans in between the 1st, and half a picture element horizontaly. All you're doing then is spliting a 810 line in 2 and transmitting both over seperate 3mhz subcarriers keeping gain, S/N ratio etc better than 819 or even 625. Result: upgrading from the world's lowest definition system to one of the highest but crucialy, enabling exisiting 405 line receivers to still work with the signal. A colour subacrrier could be added to the lower of the tow luminance signals so as not to reduce the definition of the "main" 405 signal. Cheers Tim
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15th Mar 2009, 7:21 am | #7 |
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Re: Subjective difference between 405 & 819
Re the French 819 line system E, did the receivers typically have black level AGC, or was there a tendency to use mean level AGC for simplicity, as seems to have been the case with British 405-line receivers? One might expect that with the advent of dual-standard 625/819 line receivers in France, black level AGC was used, in order to get the most out of the new 625 line system, but I wonder. On the other hand, it does seem likely that 819 line video bandwidth would have suffered in the dual-standard receivers. How were the IFs arranged? Perhaps the same vision IF for 625 and 819, with different sound IFs? And maybe with the 625 line sound IF trap permanently in place, thus limiting the video bandwidth to the same value for both standards?
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15th Mar 2009, 7:17 pm | #8 |
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Re: Subjective difference between 405 & 819
Hi
I'm not sure how the manufacturers would do the IF strip in the dual standard sets. For the 11mhz required on 819 to get reasonable gain at least one if not two more stages than on 405 line sets would be needed as the stages would be widely staggered. Its possible that on D/S sets that the band width is the same on both standards, so the picture will be better on 625 for the given bandwidth. I now have a dual standard 625/819 set which I will need to fix but I will post the results here sometime in the future. Cheers Trevor
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15th Mar 2009, 7:28 pm | #9 |
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Re: Subjective difference between 405 & 819
Hi.
To reply to Steve (Panrock) I up convert using the multistandard Aurora, but I have programmed my RT Russell Test card generator with high quality stills and to be honest although 819 is sharper than 405 at a normal veiwing distance its hard to tell between 405 & 819, strangely this set runs well on 625 and the picture quality is qute amazing! It beats both 405 & 819, must be again available bandwidth. Cheers Trevor
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2nd May 2009, 7:13 am | #10 |
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Re: Subjective difference between 405 & 819
Re the IF bandwidths of French 625/819-line dual standard colour receivers, I have found some interesting comments in Volume 2 of Carnt & Townsend (*), in the chapter on SECAM equipment. To quote: “Cheaper receivers use the same narrow-band I.F. for both standards, but the better models use a 9 MHz I.F. with a narrow-band filter after the U.H.F. tuner.”
The French normal intermediate frequencies are kindly given by jhalphen in the thread: https://www.vintage-radio.net/forum/...ad.php?t=20215, as: 819: 28.05 MHz vision and 39.2 MHz sound; 625: 32.7 MHz vision and 39.2 MHz sound; So the sound IF was common to both systems. Presumably the wideband IF strip was designed to be -6dB at both 28.05 MHz and around 37 MHz, with a deep null at 39.2 MHz. And the narrow filter for 625 lines would be -6 dB at 32.7 MHz, which combined with the wideband characteristics, would give a video bandwidth of around 4.5 MHz. Actually those numbers are a bit puzzling. One might have expected a video bandwidth of around 5.5 MHz or so on 625 lines, putting the upper -6 dB point at about 38.2 MHz, and which in turn would have allowed a 10 MHz bandwidth on 819 lines. And for narrow band only receivers, on 819 lines surely it would still be necessary to have the vision carrier (28.05 MHz) at the lower -6 dB point on the curve, in which case a wide band IF would seem to be unavoidable? What C&T have suggested in respect of narrow band only receivers would seem to work more easily had the vision IF been common to both systems, although then the sound IF would have to have been switchable to two frequencies 4.65 MHz apart. Cheers, (*) See page 231 Carnt & Townsend Colour Television; Volume 2: PAL, SECAM and Other Systems Iliffe, 1969 SBN 592 05946 4 |
2nd May 2009, 8:52 am | #11 |
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Re: Subjective difference between 405 & 819
The actual visual difference between 819 and 405 is quite small and I doubt if the average viewer would notice which system they were viewing. The sets of the 50's and 60's used the standard Mullard/Philips MW43-64/AW47-91 type of 17/19" tube and I doubt if they were capable of focusing down to such a fine spot detail as 819 would require. All my customers preferred the quality of the 405 line picture compared with the 625 line one through the early years of dual standard operation even with good sets and aerials.
The 405 line system, on a good receiver, does produce pictures of staggering quality all these years after its conception, both bright and crisp. The quality obtainable still amazes me even today after 40 years in the trade. There is no doubt a technical improvement on paper with the 819 line system but I doubt if this was realized at the end of the average customers aerial. Both pioneering systems that still hold their own today. Regards, John. |