With the kind help of an ex-BBC colleague in loaning same (thanks Phil
) I've scanned the graticule from a Gould/Advance OS3351.
After a bit of bitmap editing, I've managed to edit out most of the 'provenance' (!) so here's the end-result which I hope will be of interest/use.
Best wishes
Guy
Scanning a transparent mask sounds tricky. How did you do it?
I believe that pulse and bar tests were devised by Weaver (BBC) and McNamara (GPO) to provide a quick and simple way to assess a video path. Much easier than frequency sweep and indicates phase response too.
I cheated, I'm afraid.
This comes from IBA Technical Review 2
I've removed the slight greyish background and a slight (0.4°) tilt.
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attachment=17356]
@Jeffrey: I printed off a pure black square image (MS Paint) using my laser printer - this yielded a pretty good matt black background that I placed behind the 'scope graticule on my Epson WF-2530.
What took the time was editing out all the scratches
@Terry: that is a very nice image ... I've done a similar exercise using the original BBC D&ED drawing as a template - file herewith
Very nice indeed, Guy. As I said in my previous post I did very little to the IBA graticule, although it seems to be lacking the zero and decimal point for the 0.3V sync level.
I'm puzzled by some of the markings on those BBC graticules, though. The IBA one correctly shows modulation level with peak white at 20% and the sync tips at 100% for use with a demodulator and black level at 0.3V with peak white at 1V for video measurements, but both BBC examples show black level as 0% and peak white as 100%. One of them also shows modulation levels with peak white correctly at 20% but black level at 100%!
Can somebody pleas explain these inconsistencies because they simply do not make sense to me!
I've just looked in Weaver's TV Video and Transmission Measuements (Marconi Instruments 2nd ed revised 1979). P31 shows a P&B graticule with 30% and 100% for video plus inverted 0%, 20%, 76%, 100% for demodulated video.
This book is a valuable reference for analogue era video measurements. Including the tangential method of measuring noise.
But where are those 0% and 100% levels shown Jeffrey?
I should have both Weaver's IEE Monograph and the condensed Marconi version but don't know where they are.
Disturbingly, I didn't come across then in the recent house clearance - I hope, if they are lurking at the bottom of a box somewhere, that it isn't one that went to the skip!
Photo of the graticle from Weaver (1979). It says "alternative version" but I can't find another comparable picture. I've had a quick flip through Weaver's Monograph and can't find any graticule images anything like as good as the one I've shown.
For all practical purposes, that is identical to the TE1A-507 posted by Guy with the, to me, incorrect markings referred to black level, although the 0% level on the right-hand scale is inferred, not actually shown on either of them.
Curiously, Guy's version also shows the sync-tip level as 43%!
The 0% sync tip level is shown at the bottom right of Guy's image. The 30% mark on the right is correctly at black level on both. Not sure where 43% is on any of the images.