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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 11th Jun 2006, 10:04 am   #1
oldeurope
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Default Question in aurora v-sync switch pos. 6

Hi, there is something I don't understand. See Page 8 aurora manual
Position 6 - Equalization Pulses

In 625 the v-sync is 160 us. in front of it we have eq-pulses that takes
160 us. So the v-sync starts 160 us after the last active line.

In 405 the v-sync is 400 us and it starts without any delay after the
last active line. So the TV set has enough time for the vertical flyback
to make the first lines visible.

In both systems the compleate v-sync takes nearly the same space.

Now my question:
How can you add eq-pulses in front of the v-sync pulse without moving
the v-pulse or suppressing active lines?

In the 441 system they found a very clever way by adding only one
eq pulse after the v-sync. The v-sync is in the same position directly
after the last active line like in 405.

In 819 eq-pulses makes no sense, because an integrator can not be used
at the receiver.

Kind regards
Darius
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Old 11th Jun 2006, 10:33 am   #2
ppppenguin
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Default Re: Question in aurora v-sync switch pos. 6

I've just looked at the output of my Aurora and the active picture starts 2 lines early when the EQ pulses are turned on. This is technically incorrect but you are most unlikely to notice it on a receiver. It is visible as a slight change in vertical position on a high quality underscanned monitor as you switch EQ pulses on and off. If I looked away from the monitor, changed the switch and looked back at the monitor I doubt I would notice any change.
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Old 11th Jun 2006, 10:33 am   #3
David_Robinson
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Default Re: Question in aurora v-sync switch pos. 6

Quote:
Originally Posted by Darius
How can you add eq-pulses in front of the v-sync pulse without moving the v-pulse or suppressing active lines?
You can't! The active picture must be moved up and/or cropped to make space. There's no need for eq pulses anyway. But I guess if it was a zero cost option on the converter, and it's switchable, why not?

Just think, if eq pulses had not been added to the 625 system, we could have had 4 more lines of teletext per field!
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Old 11th Jun 2006, 10:51 am   #4
oldeurope
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Default Re: Question in aurora v-sync switch pos. 6

Thanks Jeffrey, this is what I expected, well done!

David, in 625 we definately need them because in the vintage receivers an
integrator is used to separate the v-sync.
The british sets don't use an integrator and they don't need this pulses.
Except some dual standard sets, they have an interlace adjust.

Kind regards
Darius
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Old 11th Jun 2006, 2:17 pm   #5
tubesrule
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Default Re: Question in aurora v-sync switch pos. 6

Hi Darius,
Jeff and David are correct. When the eq pulses are enabled, the image will shift slightly vertically. Since the internal sync generator already has this capability, it was nothing to allow eq pulses on all standards. It will help the interlace on some sets, but is not required on others.
For the vertical retrace time, different standards allow vastly different times for this to occur. Some early standards allowed no (0) retrace time, and there are no blanking lines between the vertical sync and the active lines. For any modern standard like 405, I doubt the 2 line shift will induce any nonlinearities at the top of the image.
For the 819 line standards, while the French version did use a single broad pulse with no eq pulses, the Belgian version used 3.5 lines of eq/sync/eq in a similar fashion to 625. Since the Belgian 819 and 625 are the only standards that used half line sync's, their field line positions are unique to all other standards.

Darryl
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Old 11th Jun 2006, 2:55 pm   #6
oldeurope
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Default Re: Question in aurora v-sync switch pos. 6

Quote:
Originally Posted by tubesrule
For the vertical retrace time, different standards allow vastly different times for this to occur. Some early standards allowed no (0) retrace time, and there are no blanking lines between the vertical sync and the active lines.

Darryl
Hi Darryl,
a Nipkow disc needs no retrace and spinns continuosly.

Kind regards
Darius
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Old 11th Jun 2006, 3:02 pm   #7
tubesrule
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Default Re: Question in aurora v-sync switch pos. 6

Quote:
Originally Posted by Darius
Hi Darryl,
a Nipkow disc needs no retrace and spinns continuosly.
Very true. I was referring early electronic standards in which there were no blanking lines. I always assumed these standards would have caused nonlinearities (bunching) of the lines at the top of the image.

Darryl
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Old 11th Jun 2006, 3:56 pm   #8
David_Robinson
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Default Re: Question in aurora v-sync switch pos. 6

Quote from CCIR Report 624-2:
Quote:
In System E, there are no equalizing pulses and only one field-synchronising pulse which starts 3H after the beginning of the field blanking pulse
Well, we know that the French like to do things differently, but what possible reason could there be for having 3 blank lines before the field sync? All it seems to achieve is to waste 3 lines...
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Old 11th Jun 2006, 4:03 pm   #9
oldeurope
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Default Re: Question in aurora v-sync switch pos. 6

Some sync separators (and DC- restorers) get in trouble if there is a jump
from peak white to black. Sync pulses are missing if the signal "lifts up" for
a moment. To make sure that the sync sep. does not ignore this v-pulse
it is better to blank a few lines before it comes.

Kind regards
Darius
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