Another Pulse–And–Bar Question!

[Chris55000]

Something that's puzzled me about the Pulse–and–Bar Test Pattern!

The one that's generally acknowledged as the full test is the one that has the five–step grey–scale widge on the right–hand side, the waveform I have reproduced from the Practical Television Supplements "TV Test Patterns and Signals", (the original cannot be copied very easily to read, so I traced it!) followed by a (idealized!) picture of its full–screen appearance – the one that more generally used to appear during early startup or after closedown was a simplified version, as shown in the third and fourth snippets!

Is this the "Line 20" Simplified VITS shown in the Practical Television Supplement?

Also, can anyone suggest :–

a) Why the right hand side is white when the waveform for line 20 shows the luminance at black–level?

b) The reason the coloured bands on the third and fourth snippets come out different colours?

I seem to remember that that the chroma output from some pulse–and–bar generators comes out as turquoise/greeny–blue rather than blue or magenta as per these shots, was that the case?

Chris Williams

[murphyv310]

Hi.
Line 20 has two levels of Chroma, cant remember the levels or the timing though, just too long ago.

Look what I found !!!!

[red16v]

From a broadcast perspective these signals were generally used for the testing of circuits rather than, say, individual pieces of kit or paths within a broadcasting facility. Within ITV the two lines of signal were standardised as the kit ‘injecting’ them onto the company’s output was supplied by the IBA and we were NOT to touch it. Internally within our studio centre we used a number of variations of what you are referring to as full screen VITS for some testing, but generally we used more specialised waveforms pertinent to the kit under test so it comes as no surprise that you are having difficulty in reconciling waveforms with pictures!

I’m s bit confused by your pictures and question, but for the line diagram you have shown this shows a 100% luma bar signal to assess luminance gain, a 2T pulse to give a limited performance parameter for circuit bandwidth (K-rating), a 10T pulse (reduced bandwidth) filled with chroma to assess luma/chroma gain mismatches and luma/chroma delay, a luma staircase with a chroma step on each level to show differential gain and phase distortion.

The pictures are really just pictures of a variation of the VITS theme.

Why does the chroma appear a different visual ‘colour’ on supposed similar waveforms? I think it would be fair to say there was no standard for the phase of the subcarrier used on the generated waveforms as it would not be relevant to the tests being undertaken, I can certainly tell you that almost all the VITS style waveforms I saw and used had no swinging subcarrier at all and so their visual appearance on a monitor would sometimes be most odd.

Murphyv310’s waveforms appear to be a 50% luma pedestal with 100% chroma sitting on top of it. If the luma and chroma gains of the circuit under test are equal then the chroma will sit at blanking (so we can easily see in his example that chroma gain is low compared to luma). Test waveforms like these were often designed so that engineers could see - at a glance- whether something was very wrong or not, just think about 100% colour bars where at first glance the bottom of the green bar should sit on blanking if chroma gain was correct(ish). The second half on the waveform shows 300mV of chroma sitting on blanking - not a signal usually generated by any production kit and so I would guess it’s purpose was to test the performance of a microwave link or transmitter and so of no use in a studio facility. I hope this helps in some way.

[Chris55000]

Textbook Oscillograms Trevor!

Still puzzled why the right–hand sides in my screenshots 3 and 4 is white tho' – would the full amplitude chroma subcarrier shown in "Television" magazine (May 1976) show up white on a TV?

I noticed that the BBC closedown pattern contains an additional white needle–pulse that isn't present in Trevor's Oscillograms which occurs before the grey–with–chroma bar, but the rest of the oscillogram matches up to screenshots 3 and 4 except for the white right–hand side, and the left hand part of the Oscillogram is exactly the same as the diagram (screenshot 1) and it's representation on–screen (screenshot 2) I posted!

I've bought a copy of the 513 page book "Television Measurement Techniques" referred to at the end of the Part 2 Supplement, but I fear that book will spawn yet more technical questions!

Chris Williams

PS!

The Tektronix TSG95, which a Member suggested I look for, generates these two Patterns exactly as per the P.T.V. Supplement, Patterns "UK ITS 1" and "UK ITS 2".

[Chris55000]

PPS!

Member "red16v", thank you for your comprehensive explanation, by the way!

I definitely will have to have a read of my book when it comes me thinks!

Chris Williams

[murphyv310]

Hi the oscillograms are lines 19 & 20.
When I was a trainee station engineer with British Relay we used off air VITS all the time. I'm not sure but I think the picture is off air with a Murphy receiver with synchronous detector type MR756 that I had some years back. Certainly the 10t pulse is low with a little Luminance Chrominance delay inequality. On screen though into a monitor it was exceptionally clean.
All a distant memory now though.

[red16v]

If you are further interested, here is a link to the operational manual for the Tektronix VITS201 which was the ‘final’ VITS generators used by us on our remaining analogue outgoing lines. Pages 4-7/4-8 show the Standard UK lines and signals (and they correct my fading memory figures of signal amplitudes). You’ll also notice it refers to the generated chroma signal as being generated at a fixed phase of 60.7 degrees (?) and by implication confirms the chroma does not swing on a line by line basis.

But do please remember these figures are for VITS signals, full field signals were likely to be composed differently as I viewed on many occasions.

https://www.tmc-direkt.de/wp-content...ix_VITS201.pdf

[murphyv310]

Originally Posted by red16v

If you are further interested, here is a link to the operational manual for the Tektronix VITS201 which was the ‘final’ VITS generators used by us on our remaining analogue outgoing lines. Pages 4-7/4-8 show the Standard UK lines and signals (and they correct my fading memory figures of signal amplitudes). You’ll also notice it refers to the generated chroma signal as being generated at a fixed phase of 60.7 degrees (?) and by implication confirms the chroma does not swing on a line by line basis.

But do please remember these figures are for VITS signals, full field signals were likely to be composed differently as I viewed on many occasions.

https://www.tmc-direkt.de/wp-content...ix_VITS201.pdf

Did you ever use the Tektronix line selector scope? It had
a standards switch 405/525/625 & 819 lines and also a line selector calibrated for VITS ( between lines 17 & 23 approx) and also a variable control to investigate frame sync and other lines of importance. Can't remember the model but would give my eye teeth for one or decent money!

[John_BS]

Is anyone interested in one of these BBC booklets?

[red16v]

Originally Posted by murphyv310

Did you ever use the Tektronix line selector scope? It had
a standards switch 405/525/625 & 819 lines and also a line selector calibrated for VITS ( between lines 17 & 23 approx) and also a variable control to investigate frame sync and other lines of importance. Can't remember the model but would give my eye teeth for one or decent money!

Working at a large TV production company we had many many items of Tektronix kit (and other makes). I recall working with the TEK WFM 521 all the way up to the TEK VM700. Such was our reliance on equipment like this we had a small section of 3 engineers whose sole role was to repair and calibrate test equipment.

What was very interesting from a professional viewpoint was the changeover from analogue video to digital video and how to measure and investigate these new fangled signals!

[Vintage Engr]

Originally Posted by John_BS

Is anyone interested in one of these BBC booklets?

Yes, very interesting . It reminds me of the various publications that Tek produced. It would be good to see the rest of it.

Like some others following this thread, I also got to enjoy the use of the Tek VM700. I had to do a lot of persuading to my boss before we finally purchased one.
The only problem with that wonderful beast, was that everything was either upgradeable by modules and/or software. We never did get all that I wanted!
I know we had PAL/NTSC, camera, (dud pixel count), Component, and possibly more.

David.

[Patrick Dixon]

Originally Posted by murphyv310

Did you ever use the Tektronix line selector scope? It had
a standards switch 405/525/625 & 819 lines and also a line selector calibrated for VITS ( between lines 17 & 23 approx) and also a variable control to investigate frame sync and other lines of importance. Can't remember the model but would give my eye teeth for one or decent money!

Maybe you're thinking of a Tek 2465 with Option 05?

Great scopes!

[Chris55000]

I won a small TSG95 (small enough to hold in one hand) sold "as–is" with some battery terminal corrosion and a label stuck inside the battery compartment warning NOT to use alkaline calls because the unit had been modified for rechargeable cells, so I'll test it when my BNC–RCA adapter arrives!

(Fortunately the S.M. is a full one with theory of operation, parts lists, circuits and board layouts in it!)

Chris Williams

PS!

"Short Form Video Test Procedures, Issue 2, 1980" available from here :–

Short-Form Video Test Procedures - BBCeng.info

https://www.bbceng.info/additions/20...2%20(1980).pdf

. . .(And that's another item reference to add to Section 256.15 "Suggestions for Further Reading" of Part 21, Chapter 256 of my T & M Theory and Repair Book dealing with the Pulse and Bar Test Signal plus the BH22 Generator! – I've written up my introduction to the Waveform and how it's used, introduced the BH22 and now in the process of drawing it's circuits out for Sections 256.3 to 256.14 of this chapter!)

[Iontrap]

Originally Posted by Patrick Dixon

Maybe you're thinking of a Tek 2465 with Option 05?

Great scopes!

I think you mean 529 waveform.
The four standard version had four coloured lights indicating system. This was a mod. Mid-60s?

[Iontrap]

Found a picture
The monitors we had were the half-rack version.