UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Television Standards Converters, Modulators etc

Notices

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

Closed Thread
 
Thread Tools
Old 10th Jul 2006, 5:32 pm   #41
ppppenguin
Banned
 
ppppenguin's Avatar
 
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
Default Re: New Aurora converter - help wanted with review

I should have spotted where 942 came from. I ran through a few possible calculations but I didn't think of multiplying by 3.

The headroom above 942 also allows for setup (pedestal) if required.

The spectrum displays look very much as I remember them. The odd harmonics are very obvious all the way to 500MHz (max frequency for my spectrum analyser). The carriers look like square waves on a wide band scope.
ppppenguin is offline  
Old 10th Jul 2006, 6:18 pm   #42
oldeurope
Heptode
 
oldeurope's Avatar
 
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
Default Re: New Aurora converter - help wanted with review

Quote:
Originally Posted by tubesrule
Hi,
It's sort of straight forward where the 942 comes from. As Jeff mentioned, 844 is the typical white point value. This is required for a normal composite signal since the chroma information can go much higher. When only a monochrome output is required, you can take advantage of more of the D/A range. Since 0-100IRE represents 16-235, or 220 steps inclusive in a standard ITU656 data stream, and using a 70/30 video/sync ratio, the sync occupies approximately 94 steps for a total of 314. Since all the interpolation math is done at 12 bits precision, I round the results to the nearest whole integer multiple that best utilizes the 10 bit D/A range. This turns out to be a multiplier of 3 which results in the 3 * 314 = 942 steps. This yields 942/1024 * 3.3V = 3.03V range out of the D/A. If I had to add composite chroma, this would need to be dropped to the more conventional 844. With the 942 number, it allows for almost 10IRE of super white in the video.
This digital range is then matched to the output stage using the set resistors R34 and R35. Between how the digital range and set resistors are calculated, you can control the gain and operating point.

I've included a couple of picts from the spectrum analyzer of the RF output.

Darryl
Hi Darryl,
thanks for the pics. Looks equal to my output. Now I am sure that everything is ok.
To get the full dynamic range in the MK III converter, I removed the syncs from the video signal and added the new sync at the output. This gives 30% more "grey steps".

Kind regards,
Darius
__________________
RADIO & TV SERVICE

oldeurope's blogs
oldeurope is offline  
Old 10th Jul 2006, 6:46 pm   #43
tubesrule
Hexode
 
tubesrule's Avatar
 
Join Date: Jul 2004
Location: Michigan USA
Posts: 325
Default Re: New Aurora converter - help wanted with review

Quote:
Originally Posted by oldeurope
Hi Darryl,
thanks for the pics. Looks equal to my output. Now I am sure that everything is ok.
To get the full dynamic range in the MK III converter, I removed the syncs from the video signal and added the new sync at the output. This gives 30% more "grey steps".

Kind regards,
Darius
That's a great way to get more dynamic range. Why bother processing the sync signals if you don't have to.

Darryl
tubesrule is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:52 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.