HD NBTV?

[Viewmaster]

With discussions on more lines and more FPS will LEDs be able to deliver sufficient light output?
Albert.

[Steve Anderson]

With discussions on more lines and more FPS will LEDs be able to deliver sufficient light output? Albert.

I can only refer you to Steve O's (Panrock) observations...and frankly, no, i doubt it light output will be a problem. We need some serious power, at this stage Steve is only at a few Watts, yet he says it's far too bright for 32 lines. We'll see the outcome of his results over the next year at 80-lines....and he's doing this in colour....

Steve A.

[Panrock]

Well... now I've got over the shock, I no longer think it's far too bright actually. I simply have got used to expecting a good visible picture in a day-lit room. I guess it is too bright though for viewing in a dim-lit room.

Such are the mounting demands of luxeons, when you are using several (I'm using twelve) it's very hard to concentrate all the light efficiently into a small aperture. However even so, you can get it pretty bright.

For example, it's far brighter than my previous mosaic of 120 superbright LEDs was, even though that was optically quite efficient, with the LEDs mounted on a converging surface and with the mixing screen arranged at a distance to just subtend the LEDs' dispersion angles.

As stated, at this convention I shall again be demonstrating good 'ol 30-line square hole colour. Thanks to Steve A's efforts (and others) the system basically is now over-engineeered for 30-lines and is loafing along. But I do like the bright sharp picture, now more linear to the edges than ever. You can now place the camera anywhere under a whole range of illumination levels and immediately get a good, convincing picture. It's like using a low power eyepiece in a telescope. You can often see more than using a high power and the viewing is much more pleasant.

80 lines will be like switching to a high power. Dimmer for a start...I anticipate that with 80-lines, the image will revert roughly to the brightness level I demonstrated last year with 30-lines with LEDs. Namely, it'll be sufficient, but need to be viewed in subdued light. But I won't be switching to 80-lines until I have discs of critically good quality. Using the 'pin' method to make the discs (as recommended in that Don Lee televisor) just won't do!

Steve O

[Viewmaster]

As I see it going from 32 to 64 lines will result in a light reduction of 1/4,
....two stops, as the 64 holes are 1/2 the dia of the 32 holes assuming disc dia is the same. Going to 80 lines is a reduction of about 1/8th in light output.
Other than Luxeons we need a steady unmodulated very very high power light source which is then area modulated as in the old sound on film variable area recorders.
This gives a picture like enclosed. (This pic was taken from book by Larner showing Bain's early experiments in static picture transmission).
Albert.

[Stephen]

This gives a picture like enclosed. (This pic was taken from book by Larner showing Bain's early experiments in static picture transmission).

This is very interesting, Albert. As best as I can count, it appears to be about 96 lines horizontal scan. There seems to be about a 3:4 aspect ratio, so that would mean about 72 lines scanned in in the vertical direction. In other words, a 72 line 4:3 aspect ratio picture would probably be about equivalent in resolution.

[Panrock]

As I see it going from 32 to 64 lines will result in a light reduction of 1/4,
....two stops, as the 64 holes are 1/2 the dia of the 32 holes assuming disc dia is the same. Going to 80 lines is a reduction of about 1/8th in light output.

Not so. For a given disc and picture shape, doubling the number of holes will mean twice as many holes squeezed into an aperture half as wide. Meaning the holes won't be half the diameter, but a quarter - and one sixteenth of the area ! Thus you lose four stops of light, not two.

So, whereas my 30 line holes are 1.4mm across, my 80 line holes are just 0.27mm. This has been a bitter price to pay for my greed for more lines!!

Steve

[Viewmaster]

As I see it going from 32 to 64 lines will result in a light reduction of 1/4,
....two stops, as the 64 holes are 1/2 the dia of the 32 holes assuming disc dia is the same. Going to 80 lines is a reduction of about 1/8th in light output.

Not so. For a given disc and picture shape, doubling the number of holes will mean twice as many holes squeezed into an aperture half as wide. Meaning the holes won't be half the diameter, but a quarter - and one sixteenth of the area ! Thus you lose four stops of light, not two.
Steve

Far be it for me to disagree with one of the NBTV masters ...but I will anyway

But I am puzzled...If I doubled the number of lines on my simple black and white 32 line NBTV to 64 holes, keeping the same picture size, I would simply half the diameter of the holes in order to squeeze double the number into the same picturewidth.
Hence the 2 stops light reduction I mentioned.

Maybe we talk at cross purposes. You with colour and stereo in mind and me with just simple black and white NBTV.
Is that the explanation I wonder or am I just thick?
Albert.

[Panrock]

But I am puzzled...

I was too. I planned my 80-line systen originally on the same assumptions you're making. I got my fingers burnt.

If I doubled the number of lines on my simple black and white 32 line NBTV to 64 holes, keeping the same picture size, I would simply half the diameter of the holes in order to squeeze double the number into the same picturewidth.

But sadly you wouldn't have room on the disc for the same picture size! Remember, you've got 64 segments to fit in around the circumference now, not 32. And within each of those ½-width segments you have to fit in twice as many picture elements as before.

I'm assuming the picture shape remains the same in both cases.

Maybe we talk at cross purposes. You with colour and stereo in mind and me with just simple black and white NBTV.
Is that the explanation I wonder or am I just thick?
Albert.

Nothing to do with colour or stereo. And by the way, it's me that has bagged the title of local thicko here, as should have been made evident by many of my past posts... That's the glory of this friendly club - I can go to the specialists who really know their oats whenever I need help.

Steve O

[Viewmaster]

om on the disc for the same picture size! Remember, you've got 64 segments to fit in around the circumference now, not 32. And within each of those ½-width segments you have to fit in twice as many picture elements as before.

I'm assuming the picture shape remains the same in both cases.

Maybe we talk at cross purposes. You with colour and stereo in mind and me with just simple black and white NBTV.
Is that the explanation I wonder or am I just thick?
Albert.

Nothing to do with colour or stereo. And by the way, it's me that has bagged the title of local thicko here, as should have been made evident by many of my past posts... That's the glory of this friendly club - I can go to the specialists who really know their oats whenever I need help.

Steve O

Ah, my penny's dropped. I overlooked the circumference.
Talking of bagging...

I am reminded of Dad's Army where Capt Mannering and Wilson are discussing the coming dance etc. Wilson claims something as he bagged it first. Mannering then talks of forming a new dance committee. ...."And I bags Chairman he claims quickly!"
I'm sure you have seen that episode.
Albert.

[Klaas Robers]

Now I see the reason why Vic Brown made a two spiral disc for his 60 line colour monitor. The disc has a double spiral of 2 x 30 holes. It runs at twice the speed (25 rps) A second disc at 12,5 rps obscures one of the spirals but the result is a 60 lines picture at the 30 line picture size.

I expect that he is bringing it to the Convention. I am curiuos to see it.

[Stephen]

There is an interesting listing of European television stations as of 1932 at http://www.earlytelevision.org/european ... _1932.html . Notice Rome has a 60 line, 20 fps system with what we would regard as a 3:4 portrait aspect ratio, even though it uses horizontal scan, and therefore renders a 2700 (45×60) element picture. The broadcast wavelength is 80 metres (3.75 mHz).

Doberitz has a nice 48 line, 25 fps system with a 4:3 landscape aspect ratio and horizontal scanning that renders a stated 3060 (48 × 64) element picture. The broadcast wavelength is 142.8 metres (2.1 mHz). This happens to be within the old 2-3 mHz American experimental television broadcasting band.

[DrZarkov]

The Doberitz-standard seems very nice to me. Remember this thread: http://www.taswegian.com/NBTV/forum/viewtopic.php?t=240 The second picture is 48 lines resolution. It is already a big improvement to 30 lines.

[Stephen]

The Doberitz-standard seems very nice to me. Remember this thread: http://www.taswegian.com/NBTV/forum/viewtopic.php?t=240 The second picture is 48 lines resolution. It is already a big improvement to 30 lines.

Yes, and 48 lines would still provide a relatively bright picture with a reasonable bandwith (38.4 kHz with a Kell factor of 1.0, 26.7 kHz with a Kell factor of 0.7). The frame rate would be high enough to minimise flicker as well as display very smooth motion. Plus, it is truly a historical standard!

[Steve Anderson]

Chaps,

I'm still undecided on what format I am going to go for, but it will be 4:3. The problem is storage, or more correctly, access to it.

48 lines...neatly fits into the bandwidth of 48kHz wave files and even an audio CD. But although Volkers pictures show what an improvement it is, just a 50% increase doesn't quite satisfy me.

60 lines...now we're getting serious, but unless using 96kHz sampling on a sound card most simple storage methods are non-starters. The built-in one on my PC 'works', but the timebase is not as stable as I would like at 96kHz. At 48kHz sampling it's very stable and only 0.003% fast.

80 & 90 lines...simply more of the above.

Over the past few days I've looked at USB flash-drives, CF cards (again), EEPROMs....all are in one way or another are a headache to interface with in what should be a simple system. Colour only compounds this problem, so does sound too.

I've looked at PCI data aquasition cards, but driving these means getting involved in some heavy software which is not my thing.

If it were not for the storage issue I would go the way of 4:3, 80 lines, left-right/top-to-bottom scanning with perhaps an increased frame rate.

I have to take my hat off to Steve O who presumably had to build both camera and monitor at the same time and de-bug them simultainiously.

....more on this I'm sure...

Steve A.

P.S. If we had DVRs here (similar to SkyBoxes), that might be a possibilty, akin the the VCR item I did a few years ago, although the compression used might be a problem.

[Panrock]

....more on this I'm sure...

Yes you can't keep me off the subject. However I'm very happily wedded to my 'new improved' 30-line colour at present. Just had it running this morning for a quick five-minute session.

With the square holes at both camera and monitor, line structure is not an issue and even the picture definition seems satisfying in a chunky sort of way. It'll be interesting to see it compared with Vic's 60-line generator-fed picture.

One bonus of Steve A's DC-fed circuitry is that the picture brightness is now 'self-adjusting'. Televising in dim ambient light results in a good picture of restful brightness from the monitor. Televising in daylight results in a picture of equal quality but now daylight-bright from the monitor. No need to adjust the camera lens stop setting... It automatically syncs itself up (including frame phasing too). Simplicity itself to operate.

Steve O