120 and 180 line viewing

[Panrock]

Work is busy, but I'm now hankering after wasting a little time again. And what better way to do this than indulge in NBTV? Though I have to say that what follows is barely "NB" tv at all...

How about "changing one capacitor" for an easy new project?

The mission: to convert my ancient 405-line Argus televisor (depicted) to display 120 and 180 line pictures, as beloved of the Germans in the early-to-mid thirties. I'd like to see how good they were. I have Darryl's World Converter to hand to supply any conceivable signal.

Here, I ask for opinions from those more knowledgeable with electronic theory than I. Is all I have to do - to change C57? (click on tb.gif to see the circuit.) Or will the linearity and width then be affected too? If so, what else is to be done?

It might be, due to the slower trace speed, my Argus will give a brighter, 'sparkier' picture at 120/180 lines than at 405. We shall see.

Steve O

[Steve Anderson]

Yep Steve, an increase of C57 would appear all that you'll need to do. How much depends on whether the 180 standard is interlaced ot not - unlikely.

However, if the 180 standard is not interlaced the vertical timebase would also need slowing down to 25Hz rather than 50.

You may also have to fiddle around with the sync separator - depends on the difference in pulse widths between the two standards. I can't see how the linearity should be affected, it is after all a 'scope with radio glued on the front end (no disrespect). Possibly C54/55 and C49/50 may need an increase...maybe.

The more I look at the circuit the more I see...perhaps also C52/53 and C49/50...again try it first, it may well be fine. I'll shut down the other monitor now to get rid of the circuit!

Good luck, let us know how you get on.

Steve A.

[Steve Anderson]

A bit more time...the R57-R60 and C54/55 and C47/48 values should be fine as is, 2M2 and 100nF.

However the C52/53 and C49/50 values are quite low - not sure why, but these may need attention if you do have linearity problems...

Steve A.

[Panrock]

Yep Steve, an increase of C57 would appear .....
The more I look at the circuit the more I see...perhaps also C52/53 and C49/50...again try it first, it may well be fine. I'll shut down the other monitor now to get rid of the circuit!

Thanks Steve. My suspicions exactly. Also from you came a timely reminder I shall have to halve the speed of the frame timebase. (Your next post crossed mine).

The two standards I shall be homing in on are: (quoted from Darryl's WC-01 manual)

180/25p 6:5 progressive electronic (TeKaDe, 1934-1939)

120/24p 6:5 progressive electronic hybrid (RCA U.S.A. experimental, 1931-1932)

I see there's a German 120-line standard available too, but this is 'mechanical' not 'electronic', probably meaning the syncs out of the converter will be separate, not composite. This would involve more work on the Argus - and it's unnecessary.

Converting the Argus to a lower definition than 405, with hopefully brighter pictures resulting, may mean I'll be motivated to use it as a regular television again... I wonder whether I will finally get to prefer 180 or 120 lines on the small screen?

Steve O

[Steve Anderson]

What I have on the RCA 120-line 24fps system I have uploaded into the 'Resources' section. I have precious little on 180 lines.

If one ignores the flicker I found only 72 lines on a 3" CRT quite viewable, so with a 5-6" CRT and 120/180 lines at 25fps should be OK...even if in this case it's monochome. (Which I tend to prefer anyway in smaller formats).

Don't suppose anyone can tell me how to turn my DumbPhone into mono? A Galaxy something-or-other...a hand-me-down from the wife...otherwise I would still be using my 10 year old Motorola but I couldn't find a replacement battery for it...ho hum...planned obsolecence? Never!

Steve A.

[Panrock]

....otherwise I would still be using my 10 year old Motorola but I couldn't find a replacement battery for it...ho hum...planned obsolecence? Never!

I found a new battery for my 12 year old Nokia somewhere online. As of last week, it's got lost. So I now have no mobile phone at all and I must say I'm not missing it.

Making up Copycoder packs today - an intensely boring job - so as a 'reward' I've pencilled in Thursday and Friday to play with the Argus.

Steve O

[DrZarkov]

The German 180/25p standard was at least the "official" standard when public TV has been started in Germany. After only one year they switched over to the 441 line standard.

[Panrock]

Hi Volker! Weren't Farnsworth cameras used at the Berlin Olympics and am I correct they were using 180-lines?

I've always thought the German 180-lines was arguably the first "high definition" system; especially because the British 405-lines could sometimes relapse into being no more than 202½ !

Anyway, hopefully later this week I shall be able to judge for myself how good 180-lines looks...

Steve O

[Steve Anderson]

...because the British 405-lines could sometimes relapse into being no more than 202½

That extra half line makes all the difference. I recall I guy I was working for about a decade ago was proud of his new Sony laptop. "It has a 15.1" screen...you know that 0.1" makes all the difference!"

He was being facetious..an ex-Sony employee...

He left of his own free will, as I did...

Steve A.

[DrZarkov]

Hello Steve, yes, that's true. At the Berlin Olympics Farnsworth cameras were used.

Here you can see the Farnsworth-camera:
http://www.youtube.com/watch?v=bcQvnWmGdew

I wonder what this type of camera this is: It is called the "Telekanone". The man at the camera is BTW Walter Bruch, the man who invented 30 years later the PAL-system:

bruchkanone.jpg (68.5 KiB) Viewed 12834 times

[Panrock]

Both the cameras you cite have very large objective lenses. I understand the Farnsworth was very insensitive, and did not embody the storage principle. I once saw some off-screen images in, I think, a 1936 edition of 'Wireless World'. The results were dark and smeary. Since it was "180-line viewing", I suppose this is on-topic for the thread.

I have just this minute located the appropriate capacitors to change, so shortly should be able to do my own "180-line viewing".

Steve O

[Panrock]

I've now had the Argus running at 120, 180 and 240 lines. The difference in the appearance of the Test Card between these standards on the small screen is not dramatic. What is noticeable is how much flicker is obvious on all these non-interlaced 24/25 Hz standards. I think the Baird 240-line trial at AP must have badly lost out against the Marconi-EMI system due to this alone!

The Argus' linearity still remains OK. Off-screen photos to follow. However, before I do, there are two problems to fix. The first is the presence of some RF 'herringbone' interference on the picture. The second is that the frame flyback is now too sluggish with C43's value tripled and the frame timebase running at 24/25 Hz. This is resulting in objectionable flyback lines, possibly due to the narrow frame 'buffer zone' on these standards. I haven't had a fiddle yet, but anyone would like to make suggestions based on the circuit posted earlier - please feel free!

I also went below 120-lines, and had a look at 96 and 90 line pictures. However, since these are available on the WC-01 only as 'mechanical' standards, separate pulses rather than composite syncs are provided. I'd need to arrange some sort of independent pulse input to the Argus for this.

Steve O

[Steve Anderson]

Rapid progress indeed!

...there are two problems to fix. The first is the presence of some RF 'herringbone' interference on the picture. The second is that the frame flyback is now too sluggish with C43's value tripled and the frame timebase running at 24/25 Hz.

This is usually some RF/IF related problem (not that the Argus has an IF), either cross-mod from another (unknown) carrier or something isn't quite stable. Or it may be the RF level is a bit high, but if it were OK on 405...

The flyback problem may be due some time-constant shortfall. First thoughts were C61 (30nF) but as this is rated for 2.5kV it may be difficult to increase the value. Also C40 (10nF) may be worth a look at. If possible have a look at the cathode of V13 and see if there's any tilt in the waveform first.

It's kinda odd that all of the SP61's in the timebase circuit(s) have zero bias (except V13), but it obviously works!

I was going to suggest providing a baseband input yesterday which if the 'mechanical' standards are not composite a simple mixer to glue on the syncs would be required. This may also help identify if the herringbone pattern is coming from the RF/video section.

Seeing you have built this as an almost exact replica of the PT article I understand if you don't wish to add other 'features' to it.

Steve A.

[Panrock]

Rapid progress indeed!

Thanks Steve A. As ever it's great to have your interest and support.

This is usually some RF/IF related problem (not that the Argus has an IF), either cross-mod from another (unknown) carrier or something isn't quite stable. Or it may be the RF level is a bit high, but if it were OK on 405...

As a start, I suppose I could simply unplug the EF50s on the vision strip one-by-one to trace where this is coming from. The RF input level should be OK. I've already set it to optimal.

The flyback problem may be due some time-constant shortfall. First thoughts were C61 (30nF) but as this is rated for 2.5kV it may be difficult to increase the value. Also C40 (10nF) may be worth a look at. If possible have a look at the cathode of V13 and see if there's any tilt in the waveform first.

Thanks - will look into this.

It's kinda odd that all of the SP61's in the timebase circuit(s) have zero bias (except V13), but it obviously works!

Yes. Who am I to question this?

I was going to suggest providing a baseband input yesterday which if the 'mechanical' standards are not composite a simple mixer to glue on the syncs would be required. This may also help identify if the herringbone pattern is coming from the RF/video section.

Unfortunately a 'mixed syncs' feed does not appear to be available from the WC-01 for the mechanical standards. Instead, you get (in essence) a choice between line and frame square waves. See the Manual ('resources' below). My converter is version 2.1.

Seeing you have built this as an almost exact replica of the PT article I understand if you don't wish to add other 'features' to it.

I am relaxed about this. After all, if it had been true to the original article it would never have worked! See HERE !

My immediate time for playing with this runs out at the end of the week. So thinking about how to get the unit to display 'mechanical' standards could possibly be tackled in a more leisurely way, over the weeks to come?

Resources:

Complete Argus Details

World Converter WC-01

Steve O

[Steve Anderson]

Unfortunately a 'mixed syncs' feed does not appear to be available from the WC-01 for the mechanical standards. Instead, you get (in essence) a choice between line and frame square waves. See the Manual ('resources' below). My converter is version 2.1. ...I am relaxed about this. After all, if it had been true to the original article it would never have worked! My immediate time for playing with this runs out at the end of the week. So thinking about how to get the unit to display 'mechanical' standards could possibly be tackled in a more leisurely way, over the weeks to come?

Steve O

"Sounds like a plan, Stan". I'll have a look at the WC-01 manual and post what I might do myself here...

As for "if it had been true to the original article it would never have worked!". That's quite true of many publications over many years, including the ultimate authority "Wireless World". Years ago I dare not call into question anything they published. I recall an article in WW in 1969 which was basically a re-work of an old 5CP1 'scope. When at that time I was 13 I read and re-read it time and time again. I thought it was brilliant! I was going to build this one day.

In my moves around the world I lost that copy of WW and just a few years ago I posted a request on this forum if anyone had said issue of WW. Anyway, I found a guy who willingly scanned said item.

When I sat down and re-read it after more than 30 years I realised it was a non-starter. It could never have functioned as published. I was amazed by the errors and basically poor design - even giving allowance for the fact it was probably built/tested/written in 1968. Where were the WW proof-readers? Down the pub?

It makes one wonder how many attempted this (or the "Argus") and gave up?

Steve A.

"Armchair designers" falls to hand easily...though the "Argus" was obviously built by someone as a prototype, I suspect that the article i'm referring to was actually built by the authors minions and poorly documented.