modulators and other standards and converters in general discussed

[oldeurope]

Good morning,

this is continued from the thrad:
https://www.vintage-radio.net/forum/...ead.php?t=6746

My Sony dual standard 819/625 is not modified. I'll take a photo of it for
you. It is in my store room. (Hope the tube is not imploded.)

In 819 there are two RF standards. Standard E 10MHz bandwidth and
standard F 5MHz bandwidth.
Please note the bandwidth is limited by the sound and color carrier.

Look at the americans. They have the same line frequency like we have
in Europe. (16KHz)
So the same bandwidth gives the same horizontal resolution.
They can only use 2,5MHz practically and this is why pictures from
statesite look so poor. It is not the account of lines that causes this.

I think in 819 it is not possible to record something with full resolution.
Remember how great a 405 vhs recording looks and at 625 it is acceptable
and I guess in 819 it will be very bad.

Conclusion, the lower the line frequency the higher is the horizontal resolution.
I think 625 is the best compromise and it don't makes sense to me to transmitt
the new HDTV. You'll better use a line doubler to get from 625 to VGA standard
at the receiver side. This solves the problems in a better way.
The 16:9 increases the vertical resolution, so you need a higher horizontal resolution
too.
In 625 16:9 you need ca 10MHz what do you want in HDTV? 30MHz?
They will reduce the data rate so much to make this possible.
I don't like it.

Kind regards
Darius

[channel405]

Hi Darius,

Yes a photo would be good thanks.

I understand what you say about resolution verses line frequency. Excuse my dimwittedness though, but if you had a line doubler in a receiver, to save transmitting the extra resolution and thus saving bandwith, how would you transmit the extra detail to fill up those lines if you get my drift? Would you simply repeat the previous line? There are systems that do scaling like that now, TV cards in PCs for example and huge display etc but the pics don't have anymore detail, just less line structure. Or am I missing something?!

And 16x9 increases horizontal res I thought due to an increase in pixels on each line? There is no doubt about the compression issue though, but that is one of the major drawbacks of the digital world I suppose. Bring back HDMAC is say!!

Tim

[oldeurope]

Originally Posted by channel405

Hi Darius,

Yes a photo would be good thanks.

I understand what you say about resolution verses line frequency. Excuse my dimwittedness though, but if you had a line doubler in a receiver, to save transmitting the extra resolution and thus saving bandwith, how would you transmit the extra detail to fill up those lines if you get my drift? Would you simply repeat the previous line? There are systems that do scaling like that now, TV cards in PCs for example and huge display etc but the pics don't have anymore detail, just less line structure. Or am I missing something?!

And 16x9 increases horizontal res I thought due to an increase in pixels on each line? There is no doubt about the compression issue though, but that is one of the major drawbacks of the digital world I suppose. Bring back HDMAC is say!!

Tim

Good evening Tim,
all a question of good interpolation.
Not that doubling 625 gives progressive scan.
Because of limited bitstream it is not possible to transmitt moving
images in the 625 line standard with full details. So how do you want to
do this in HDTV?
You need 1111 pixels in a 16:9 picture.
In a 4:3 you need 833 pixels.
Attached some pics of the Sony 625/819 set.
The tube is ok.

Kind regards
Darius

[David_Robinson]

Originally Posted by channel405

There are systems that do scaling like that now, TV cards in PCs for example and huge display etc but the pics don't have anymore detail, just less line structure. Or am I missing something?!

It was established by subjective tests a long time ago, that the line structure reduces the apparent vertical resolution. If the image is interlaced, the apparent resolution is even lower. A scaler converting to a higher line standard and/or progressive scan will therefore give subjectively more resolution in the vertical direction, at least in theory.

This is why the 625 standard was designed with more lines but lower horizontal resolution. Subjectively, on a conventional analogue display, the H and V resolutions were designed to match. There are 576 active picture lines - to match this number of lines (per picture height) horizontally, you would need a bandwidth of 7.3MHz (4:3 picture) or 9.8MHz (16:9 picture) rather than the actual standard of 5.5MHz.

This issue was not understood when the 405 system was designed, so it was given too few lines and too much horizontal resolution, for the bandwidth available. If you take the ratio of H to V resolution used on 625, and apply it to 405, you would only need 2.3MHz of video rather than 3MHz.

[ppppenguin]

David Robinson is indirectly referring to the infamous Kell factor. Somewhere I have the original paper written by Kell et al in 1934(?) in which he introduces this subject. The Kell factor is the ratio between the subjective vertical resolution and the actual number of lines. It can only be determined by subjective tests. It is commonly assumed as about 0.9 for progressive scan and 0.7 for 2:1 interlace. I strongly suspect that it also depends on the type of display and camera. The original work assumed scanning with gaussian spots. This is true (or nearly so) with CRTs and camera tubes. It's certainly not true with LCDs etc. LCDs have near uniform brightness distribution across each pixel with a small gap between pixels.

As David correctly states, the 405 standard has excess horizontal resolution. If I've got the dates right, Kell's work was known to the M-EMI team when they set the System A parameters. It is possible that they believed that improved technology would justify the excess bandwidth.

Line doublers are a bit like spot wobble. You don't get any more real resolution but you can improve things subjectively. You can also muck things up since de-interlacing and line doubling can introduce all sorts of artefacts. Just look at some LCD TVs as objects start to move! You really need to do a direct comparison with a CRT display as video compression systems can also give motion artefacts.

[channel405]

Thanks for the photos Darius, I notice your 819 Sony has the video input box on the side if I am right? Have you ever used it on 819 lines?

What David was reffering to is quite interesting actually, I recall that spot wobbles devices were never popular amongst veiwers as the line structure seen from the a reasonable distance form the screen gave the picture a sharper edge, especialy if the focus was good.

A well set up 405 line TV/monitor showing a picture from a good source can be pin sharp. 405 line telecine machine gave particularly good pictures. I have often thought that watching 405 instead of 625 you are not really missing anything (other that colour of course) if set up properly with good interlace.

It could be aurgued that if we stuck with 405 and used modern techniques such as receiver line doubling/interpolation with modern displays were beam spots do not distort at high brighness, it would have been more than adequate. In fact 3Mhz video compressed into a MPEG2 data stream would mean more channels of rubbish! But then atleast we would have 405 line 4:2:0 component colour rather than subcarrier based PAL that reduces the 625 line resolution even further. Oh, and stereo sound!

[ppppenguin]

Originally Posted by channel405

It could be aurgued that if we stuck with 405 and used modern techniques such as receiver line doubling/interpolation with modern displays were beam spots do not distort at high brighness, it would have been more than adequate. In fact 3Mhz video compressed into a MPEG2 data stream would mean more channels of rubbish! But then atleast we would have 405 line 4:2:0 component colour rather than subcarrier based PAL that reduces the 625 line resolution even further. Oh, and stereo sound!

My April Fool article in the April 1988 issue of "Television" 405-MAC: A new approach to compatible HDTV made very similar assumptions. It predated MPEG so I utilised MAC, a technology that is now totally obsolete.

I sometimes wonder if the apparent sharpness of some very good 405 line pictures was actually an illusion. If you can see a well focussed line structure I suspect that the picture may appear sharper than it really is. Until you try to look at fine vertical detail which isn't there or is badly aliased.

[oldeurope]

Originally Posted by channel405

Thanks for the photos Darius, I notice your 819 Sony has the video input box on the side if I am right? Have you ever used it on 819 lines?

What David was reffering to is quite interesting actually, I recall that spot wobbles devices were never popular amongst veiwers as the line structure seen from the a reasonable distance form the screen gave the picture a sharper edge, especialy if the focus was good.

A well set up 405 line TV/monitor showing a picture from a good source can be pin sharp. 405 line telecine machine gave particularly good pictures. I have often thought that watching 405 instead of 625 you are not really missing anything (other that colour of course) if set up properly with good interlace.

It could be aurgued that if we stuck with 405 and used modern techniques such as receiver line doubling/interpolation with modern displays were beam spots do not distort at high brighness, it would have been more than adequate. In fact 3Mhz video compressed into a MPEG2 data stream would mean more channels of rubbish! But then atleast we would have 405 line 4:2:0 component colour rather than subcarrier based PAL that reduces the 625 line resolution even further. Oh, and stereo sound!

Good evening,
where is your stereo sound carrier? In germany one sond chanel (mono)
is at 5,5MHz and the other (new added stereo at 5,75MHz).
The second carrier makes it difficult to tune none Intercarrier sets.
How do you call them? Parallelsound?
This is why I prefer a mono modulator.

No I have only seen the 819 raster or better a white screen.
The lines are not visible in 819 on this small screen.

If the electron beam is bigger than a line, you get a much better
resolution in an interlaced picture than in a progressive scan picture.
This is an importand fact!
Please note, in the early days the screen was small and the plate voltage
was low. Under these conditiones interlace brings a much better resolution.
At this point of view the Kell factor makes no sense, it is wrong here.

So on the little Sony a 819/25i picture will have more resolution than
a progressive scan picture.

Kind regards
Darius

[Nickthedentist]

Originally Posted by Darius

Good evening,
where is your stereo sound carrier? In germany one sond chanel (mono)
is at 5,5MHz and the other (new added stereo at 5,75MHz).
The second carrier makes it difficult to tune none Intercarrier sets.
How do you call them? Parallelsound?

Is this the "Zweiton" system that I've sometimes seen referred to in european TV manuals? We don't have an equivalent here so there's no word for it that I'm aware of.

In the UK, we use 6.0MHz for mono sound, but with conventional terrestrial analogue TV sets which have stereo sound, the NICAM (digital) sound system is used instead (and has been for the last 15 years or more, I think), which has a 6.552MHz carrier.

Nick

[oldeurope]

Originally Posted by Nickthedentist

Is this the "Zweiton" system that I've sometimes seen referred to in european TV manuals? We don't have an equivalent here so there's no word for it that I'm aware of.

In the UK, we use 6.0MHz for mono sound, but with conventional terrestrial analogue TV sets which have stereo sound, the NICAM (digital) sound system is used instead (and has been for the last 15 years or more, I think), which has a 6.552MHz carrier.

Nick

Ah, thanks for the info Nick.

But the parallelsound has nothing to do with stereo.
The PYE LV20 has not intercarrier sound, it has (how do you call this)
sound. The modern sets have (Quasiparallelton) how do you call this?

In GB you have more space between color and sound.
It is toled that the PAL color in GB has the best quality.

Kind regards
Darius

[ppppenguin]

Intercarrier sound only works with negative vision modulation and FM sound. With positive vision modulation the sync tips are at zero carrier amplitude so the intercarrier would disappear at these times. With AM sound you would not be able to limit the intercarrier to remove vision information. The buzz would be horrible!

System A has positive vision modulation and AM sound. This is why all 405 line TVs had separate sound IF. I think the best English term for the opposite of intercarrier sound is separate sound. I'm not sure how to translate Quasiparallelton.

The main benefit of intercarrier sound is immunity to local oscillator drift. This was a big problem with early UHF tuners and could completely detune the sound while the vision was perfectly OK. Now all sets have AFC or synthesised tuning there is little benefit from intercarrier sound. Perhaps some small saving by not having a separate sound IF amplifier.

Britain (and Eire and South Africa) use System I with 6MHz sound/vision spacing. This give a small theoretical improvement in picture quality. Perhaps the greatest benefit was before SAW IF filters. It was easier to design the IF filters to give a flat vision response with 6MHz sound spacing.

[channel405]

I remember reading that article Jeff, as a young (and impressionable!) apprentice engineer back in 1988 whilst battling with a Thorn 3000 PSU fault! I did my training was in a workshop for the local education dept where we looked after the counties schools receivers. Remember them with their big isolating transformers and BNC video inputs for reel to reel VTRs? Most were dual standard 1400 chassis 24" monsters but some were colour sets, mostly early Thorn 3000 single standard chassis, but thats another story.

I remember thinking, I am a fan of 405, but why 405 MAC? This may have been a joke, but actualy when you think about it, its not such a loony idea! At least you wouldn't be swamping what little high frequency end of the 405 video signal with a colour subcarrier as you have now pointed out.

Darius, are you saying that 819/25i is higher resolution on a smaller screen than 720/25p? I had never thought about like this, but then again I suppose all 720/25p displays will be plasma/LCD which are native progressive and was developed with this in mind.

[ppppenguin]

Originally Posted by channel405

I remember reading that article Jeff, as a young (and impressionable!) apprentice engineer back in 1988 whilst battling with a Thorn 3000 PSU fault! I did my training was in a workshop for the local education dept where we looked after the counties schools receivers. Remember them with their big isolating transformers and BNC video inputs for reel to reel VTRs? Most were dual standard 1400 chassis 24" monsters but some were colour sets, mostly early Thorn 3000 single standard chassis, but thats another story.

I remember thinking, I am a fan of 405, but why 405 MAC? This may have been a joke, but actualy when you think about it, its not such a loony idea! At least you wouldn't be swamping what little high frequency end of the 405 video signal with a colour subcarrier as you have now pointed out.

Glad you enjoyed the article. I was at Royal Television Society Lecture not long after I wrote it and I heard 2 engineers (who should have known better) discussing my article as if it was for real

The schools sets I remember were the mighty 25" Deccas as supplied to the Inner London Education Authority. Most had a video input panel (UHF, not BNC) on the side and were used with Sony CV2100ACE VTRs.

Originally Posted by channel405

Darius, are you saying that 819/25i is higher resolution on a smaller screen than 720/25p? I had never thought about like this, but then again I suppose all 720/25p displays will be plasma/LCD which are native progressive and was developed with this in mind.

I disagree with Darius's assertion that 819/25i will look better than 720/50p. I hope you meant 720/50p and not 720/25p. 720/25p will have problems with motion - it will look rather like film! There is considerable debate in the industry as to whether 720p is truly HD. Doesn't seem much more than 625. To make a sensible comparison it's 576 lines versus 720. The general consensus is that for the same number of lines, progressive looks better than interlaced. A few people dissent from this view.

The "gold standard" is 1080/50p (or 60p). Unfortunately this is still largely under development except for some film transfer work. In the studio it requires dual HD-SDI interconnects with a total data rate of almost 3Gbits/sec. HD as practised now is either 1080i or 720p, with almost any field rate you want. There is also 1080p with 24,25 or 30 frames per second. The interlaced standards are probably better for sport and other fast moving material. The progressive standards completely eliminate interlace artefacts and are probably better for drama. The problem will be solved when 1080/50p is available.

[Nickthedentist]

Originally Posted by ppppenguin

Glad you enjoyed the article. I was at Royal Television Society Lecture not long after I wrote it and I heard 2 engineers (who should have known better) discussing my article as if it was for real

Fooled me too! Presumably the "universal replacement transistor" one more recently was a spoof too?

[ppppenguin]

Originally Posted by Nickthedentist

Fooled me too! Presumably the "universal replacement transistor" one more recently was a spoof too?

Don't know that one and we're getting OT.

Back to interlace etc. The whole debate over the best standards for HD is a very complex one. Interlace was the original compression system and was a great invention in the 1930s. Unfortunately it is now a problem. Because interlace gives ambiguity between vertical and temporal information it is very difficult to accurately de-interlace all pictures. Accurate de-interlace is vital for the highest quality standards conversion, video effects etc. It is also essential in every LCD TV where cost conflicts with quality. The computer world has always wanted progressive scan. The future is undoubtedly progressive but interlace will take a long time to die.

I remember working with different standards in 1985. I was then working at Thorn-EMI research labs. We could display 625/50i, 1250/50i, 625/50p and 625/100i. 625/50p was lovely. No interlace artefacts at all. 625/100i was also good. No large area flicker (not a problem with LCD but we didn't ahve those then) and the interlace effects were at 50Hz which made them much less nasty. 1250/50i still had 25Hz interlace artefacts which I thought were horrible. All of these were up-converted from 625/50i, so we were looking mainly at displays rather than whole systems. I left before the end of the project and Thorn-EMI then sold Ferguson (to Thomson) so isssume the research work was aborted.

[channel405]

You are probably right Jeff aboyt the UHF rather than BNC connectors on the old school sets. Sadly I saw those of these scrapped even though they worked. We had Sony and Akai VTRs including a few colour ones, of I think the EEIJ (or something) format.

When refferring to 720/25p I had the JVC HDV1 format in mind as that will do 1280 pixels x 720 lines (Sony do 1080i only, known as HDV2 format) at 720p/24, 720p/25, 720p/30, 576p/50, 576p/25, 576i/50. But then again this is a highly compressed format of 25Mbs. Whereas HDCAM (1080) and DVCPRO HD (720 vari frame) have no compression at 100Mbs. So the artifacts will be quite apparrent, but more so on 1080i as there is more to compress. I understand most European broadcasters will go for 720p where as most US are going 1080i. All recent displays should handle both.

This brings us neatly back to 819 lines. Interlace on a larger screen really means that at any one time you only have half the number of line on the screen, and thats where the persistance of vision is supposed to come in isn't it? Progressive on 405 would have eliminated the visible line structure. It is no doubt true that it is an "illusion" of a sharper picture with some line structure. Perhaps thats why many preffered sticking to 405 when 625 first appeared, that coupled with the poor quality of the first receivers and "odd" programming on BBC2!

[David_Robinson]

Originally Posted by Darius

The modern sets have (Quasiparallelton) how do you call this?

We call it... Quasi Parallel Sound! This of course is where there are 2 separate IF strips, one with the frequency response optimised for vision (vestigial sideband, plenty of sound rejection) and one optimised for intercarrier sound (a narrow peak at the vision carrier and another narrow peak for the sound carrier(s)).

[oldeurope]

Originally Posted by David_Robinson

We call it... Quasi Parallel Sound! This of course is where there are 2 separate IF strips, one with the frequency response optimised for vision (vestigial sideband, plenty of sound rejection) and one optimised for intercarrier sound (a narrow peak at the vision carrier and another narrow peak for the sound carrier(s)).

...and the sound DF is mixed by a multipler from the limited vision carrier.

OK, thanks David.

Kind regards
Darius

[oldeurope]

Good evening,
talking about the low cost aurora again.
On the aurora website I have seen the modulator covers systems M and A.
What about the french channels?

When I made my converter, I had some trouble with RF noise from the
clock divieder in the RF output. At the end I solved these problems.

But in an digital converter there is much more noise, because it is
digital.

It is easy to screen something in a way that there is a clean signal
window. But over the whole VHF region it will be difficult

When I made my converter and modulator perfect, I had still
some noise. It came from my digital set top box via the video cable (!)
This is the reason why the modulators in these boxes not cover VHF.

The non superhet sets, LV20 TS1105 catches off channel noise because
the selectivity is not as good as in a superhet. For example if you have some
off channel noise, the pic is ok on the TV22 and the FV1 but there is a
little moire on the LV20 and TS1105.

I tested the axing modulator, it uses the motorola multistandard IC
David Robinson used in his modulator.
I tested two of them with different layouts and IC versiones.
It goes from ch 5 to UHF (CCIR). It definatly generates noise at the
low VHF frequencys. It is just not visible at ch5.
From ch7 to UHF it is perfect.
Now I know why it does not cover ch2-4.
Sorry but I don't believe that PLL multistandard modulators are really clean
at the low VHF frequencys until I have seen the output on the analyzer
and a pic on a TV set. Maybe it is because I am much more pretentious
than a non technical person. (I am a ham, DD3ET)

Kind regards
Darius

What do you think?
know why they don't go to the lower VHF channels.

[tubesrule]

Hello all,
Just to give a quick update on the converter, it is presently being redesigned to accomodate much of the feedback that I have received over the past few months. These changes may have an impact on the price rasing it to around $250 USD. The two major changes have been the addition of a bypass feature allowing the unit to act as just an RF modulator, disabling the converter, and the addition of a second modulator chip to handle more RF systems. With only one RF modulator, I was able to handle most RF systems including A, L and M, but not E, and this has been one the most requested systems.
While providing a variable side and out-of band filter to match the programmable RF modulator is posible, no effort is being spent on this as the unit is intended to only be connected directly to a television, and should never be broadcast without proper filtering. A filter of this type would substatially increase the cost of the modulator while providing no real benefit in the intended application.
Also, the main chip used in the design is brand new, and while it has been promised to be shipping for over 9 months now, it still is not available in anything other than engineering samples. While I could use a different part without loosing functionality, this one is fairly key to keeping the cost down. One final note is that it may be benficial to ship the unit without a power supply to save cost in shipping. The unit will require approximately 6-9VDC at 250ma, and without including this with the unit, the shipping weight will be just a few ounces making it very cheap to ship.
On the subject of noise, digital systems rarely generate noise that can not be readily addressed. Noise generated in digital IC's is almost alway caused by the inductance of the connections from the die to the circuit. This includes the lead frame of the device, the connection type to the circuit, and the impedance of the circuit. Proper bypassing, power plane design, and connections on the power and grounds can remove or reduce all but the lead frame inductance which are extremely low on small surface mount packages. This is why using smaller size packages is not just a matter of reducing the overall size of the product, but also in reducing lead and inter-connect inductances.
Some of the broadcast equipment I have designed resides in some of the noisiest environments possibly, that of the interior of a personal computer. Getting true 10 and 12 bit analog performance can be challenging, and at times I have come across certain PCI cards (mostly AGP and PCIe graphics cards) that are just so noisy we can not guarantee performance of our designs, but's that's a rare condition.

Darryl