Labguy's NBTV project program on YouTube

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Labguy's NBTV project program on YouTube

Postby Labmeister » Wed Jun 12, 2019 3:43 pm

I am doing a new video series on YouTube (videolabguy channel) and all of YOUR
input now will be greatly appreciated and acknowledged.

I saw that some of my articles were causing confusion for some members.
Apologies. I am attempting to be as simple as possible.
Be warned, I have an extensive background in broadcast video television equipment design
and an absolute loathing of "spaghetti" schematics. :)

What does the community consider the standard polarity for 32 line NBTV sync?
Positive or negative? Makes no difference to me, but I will need to know.
I can and will design my circuits to work "upside down" if positive sync is the rule here. Signal polarity? No problem!

Since you all seem to use audio sources, like sound cards and CD/multimedia players, it
will be presumed that your signals are AC coupled? High impedance? Voltages over a broad range?

I will be using my Aurora World Converter. Please note:
1. The outputs are all 1Vp-p, negative sync or black, terminating (properly) into 75 ohms.
2. The outputs are all DC coupled, completely eliminating the need for DC clamp circuits.
3. DC coupled outputs also make sync separating as simple as it gets.
4. I will have to build a DC to AC coupled driver to emulate the interfaces commonly used by others.(?)

My project goals are:
1. Cover the NBTV signal in great detail.
2. Build a flawless sync separator with perfect pulse separation of line and frame pulses.
3. Build a 3 phase (quadcopter / disk drive) motor driver that runs dead on 750RPM from the get go before servo feedback is added.
4. Build a phase controller that locks the Nipkow disk to the sync as near to instantly as possible.
5. Demonstrate and build a video to LED driver that is remarkably simple. And linear.
6. Demonstrate an adaptive gamma circuit that covers both positive and negative ranges for driving my linear LED driver.
(This last one allows for gamma compensated signal designs to be easily accommodated)

Sound interesting?

Richard Diehl, Labguy, Labmeister (on this group and Ebay), and Videolabguy on YouTube (all one guy!)
"Television? The word is half Latin and half Greek. No good can come of it." - C.P. Scott
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Re: Labguy's NBTV project program on YouTube

Postby Steve Anderson » Thu Jun 13, 2019 1:34 pm

Hi Richard, and welcome to the forum...

As a generalisation NBTV baseband video is AC coupled, primarily due to the signal being recorded and played back on audio devices. Even in the era of Baird the output of radios would have been AC coupled. The usual method to overcome this is DC restoration, with varying degrees of success. Others are some form of subcarrier either FM (akin to SSTV) or AM. But with NBTVs requirement of roughly 10kHz of baseband response puts the subcarrier outside of what could be called audio.

Other methods considered have been frequency-shifting where the signal (in this case) is shifted up by say 20Hz on record and down by the same amount on playback. These devices find application in PA systems such that the PA level can be increased before howlround occurs. (Only shift up in PA systems, you don't notice the shift on speech, and it's usually only around 5Hz of shift).

Digital methods are promising but the data rate can get quite high. Also the average 'sound-card' on a PC is AC coupled in and out. A custom built device is required for this.

As you know the signal polarity is the same as broadcast standards, peak white being the maximum positive excursion, sync-tips being the most negative. !V/75R is a standard, but few adhere to it. Domestic audio gear is anything but standardised in terms of level and impedance. Some believe it is, but in reality it simply isn't. The 1V standard doesn't included any composite colour subcarrier encoding (PAL, NTSC or SECAM). Polarity is also an issue, with domestic gear you put a positive polarity signal in, the chances of you getting the same out are about 50%,

I admire your goals and wish you the best. I've done a few Gamma encoding/decoding circuits in the past using the logarithmic relationship of a Vbe junction or a break-point transfer function. Easier (and more stable) is a look-up table in the digital domain. Karen Orton has also done an analogue variable encoding/decoding Gamma circuit too in one of the newsletters.

Anyway, we look forward to your input...

Steve A.

P.S. I've just noticed I have this site bookmarked for years...
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Re: Labguy's NBTV project program on YouTube

Postby Harry Dalek » Thu Jun 13, 2019 8:15 pm

I Richard great to see you on the forum ! :wink:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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