NBTV for PMR446

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

NBTV for PMR446

Postby Lowtone » Wed Oct 21, 2020 3:20 am

Hello,

Do exist a special version of full NBTV by software that can be adapted for walkie talkie transmission ?
I vaguely remind there was a low framerate format for that.
Can this be adapted for colour ?

Or even if it's not sent line by line like SSTV, is it possible to make a full digital software with codecs like mpeg ?
I guess it can embed colour and only transmits Intra frames, where the recieving software can recontruct the pictures and interpolate enough frames to have a smooth motion ?
Or even audio too?

I have those ideas but i'm not a programmer.
What do already exists, what can be done and do someone is working on this ?


thanks
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Re: NBTV for PMR446

Postby Klaas Robers » Wed Oct 21, 2020 8:24 pm

Yes, of course there is something that fulfills almost all your wishes. It uses the mpeg encoding, that you suggested, including colour and sound, and you can receive it with a so called "smart phone". In many cases the video is stored by "You Tube". It even gives more lines than NBTV, and gives more resolution.

The only limitation is that you cannot watch it using a Nipkow mechanical scanner, but why would you do that?
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Re: NBTV for PMR446

Postby Lowtone » Thu Oct 22, 2020 3:22 am

Is this irony ? :roll:
What happened to this forum ? :x
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Re: NBTV for PMR446

Postby Klaas Robers » Thu Oct 22, 2020 5:34 pm

Yes, this is more or less irony, but it is also exactly what you were asking for: do everything in software in a computer, including colour and sound, using mpeg. That is You Tube.

I don't like developments completely based on computer software. SSTV has been also kidnapped by the computer, with more lines, more resolution and with colour. Transmission of one picture takes ages and the picture quality is still inferiour to jpeg on the internet. A Japaneese ham radio operator once suggested to transmit only an internet address over radio and then your computer gets and shows the jpeg image on that address. And that then would be the new SSTV. Happily this was refused as a new standard for SSTV.

You can also transfer an internet address via PMR446 and use the same Japaneese trick. To my opinion it has nothing to do with NBTV nor SSTV.
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Re: NBTV for PMR446

Postby Steve Anderson » Fri Oct 23, 2020 12:25 pm

Klaas Robers wrote:I don't like developments completely based on computer software. SSTV has been also kidnapped by the computer....

So true. There is a time and a place for software driven applications, I use quite a bit myself in embedded microcontrollers, but to hand it over wholesale to a PC or similar defeats the purpose IMO. The PC is an incredibly useful tool, this forum wouldn't exist without them for example. Writing the code for those micros already mentioned would almost be impossible too, or at best arduous.

If you refer to the aims and objectives declared by the ARRL and the RSGB for example, there's reference to 'self-learning' and many other valuable skills and knowledge to be gained by self-learnt research, education and 'doing things yourself'. Very much hands-on.

I did have a UK Amateur Radio license (G1CLW), but that has long expired since I moved to Asia in the late '80s. For me there's little incentive to get one here, I could...but...(Ask me why in a PM if interested).

There's little to be learned by buying a commercially made 'rig' and flinging up a length of wet string (Antenna). However, it satisfies a large percentage of operators, so who am I to criticise? It's better to have a large number of active members rather than just a few who know how to use a soldering iron.

Rant over.

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Re: NBTV for PMR446

Postby Lowtone » Sat Oct 24, 2020 9:40 am

I don't want to use a smartphone or youtube.
I have a friend who use PMR446 who experiments with standard SSTV.
We don't use it as a mobile device.

But i prefer moving pictures over still pictures.
I vaguely remind that there was a NBTV mode for that.

Then i'm wondering, this is my main concern, how to squeeze pictures in this small bandwidth.

Then i got other ideas, like if the framerate is low, can the decoding software reconstructs the picture by guess ? adding more frames
I know results would be very poor, but can be interesting to improve.

This should be all electronic, no disc needed, this is why i posted in the Electronic forum.
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Re: NBTV for PMR446

Postby Steve Anderson » Sat Oct 24, 2020 11:07 am

For interesting developments in various recent non-mechanical low-bandwidth TV, this video by Chris Long is worth the one hour it takes to view:-

https://www.youtube.com/watch?v=r2YY2jFVeHo

The link was published in the NBTVA newsletter Vol. 44 No. 1.

I'm particularly interested in what I've dubbed 'Half-NBTV', same basic parameters as NBTV but at half the frame rate, for more details, view the video.

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Re: NBTV for PMR446

Postby Lowtone » Sun Oct 25, 2020 2:45 am

Steve Anderson
thanks a lot, this is the system i reminded, it would be nice to see if it can be improved
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Re: NBTV for PMR446

Postby Steve Anderson » Sun Oct 25, 2020 10:46 am

Lowtone wrote:...it would be nice to see if it can be improved

Within the constraints of 32x48 pixels at 6.25fps I doubt it could be 'improved', unless some form of compression algorithm was applied. Not forgetting you also need some way of conveying the audio stream too...which in fact requires more data/bandwidth than the video!! Instantaneous A or mu-law compression may assist, as used in international phone calls..usually at 64kb/s (Kilo-bits/second).

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Re: NBTV for PMR446

Postby Lowtone » Mon Oct 26, 2020 2:53 am

With this low framerate, other things can be done.
The decoding software can buffer the frames for about 2 seconds.
Interpret them as if they were Intra frames, and reconstruct by guess work the missing frames.
This can achieve smoother motion ( at the expensive of possible artefacts )
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Re: NBTV for PMR446

Postby Steve Anderson » Mon Oct 26, 2020 12:59 pm

'Guessing', us old fossils remember using slide-rules in maths and science classes at school, known as "Guessing to three decimal places."...or was it two?

Andrew may be able to clear that up...

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Re: NBTV for PMR446

Postby Klaas Robers » Mon Oct 26, 2020 9:52 pm

Steve, you could read two decimal places and guess the third decimal place. In fact this is suited very well to the engineering practice, where two three places is in most cases more than sufficient.

In the course that I give to men that want to pass the examination for ham radio, I alway have to tell them that in electronics a precision of 10% is enough. This makes calculations by mind much easier. 3 x 3 = 10, because 10 is a much easier number to do successive calculations than 9. And 9 = 10 with the precision of 10%. The slide ruler is much more precise. The current calculator is far too precise. Who needs all those decimals?

A former collegue of mine always stated that only the first number is important, and the position of the decimal point.
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Re: NBTV for PMR446

Postby Lowtone » Tue Oct 27, 2020 2:52 am

I got an SD card malfunction with a modern camera. The result was dropped frames here and there.
I tried to recover them in Premiere Pro.
Stiching the last good frame before the error and the first good frame after, then slowing down these two frames to close the gap.
There are several methods, but the morphing one is kinda interesting.
This is what i meant by guessing.

Or the technology use in GOP with vectors.
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Re: NBTV for PMR446

Postby Steve Anderson » Tue Oct 27, 2020 4:30 pm

Klaas Robers wrote:The current calculator is far too precise. Who needs all those decimals?

True, when you consider that most electronic devices use 10% resistors and often more than 20% capacitors it all takes on a sense of perspective. Discrete transistor gain...we won't even go there! A lot of variations are ironed out by negative feedback, but that's also subject to component tolerances. Precision, should you need it, is often the realm of crystals and number-crunching chips. I believe the entire Apollo program was calculated to less than eight decimal places, and in large parts less than four.

There are of course many places where accuracy is required. If you set up chat/schedule on 144MHz there's little chance of success if you're 25kHz off-frequency, or about 0.017% off.

There are times and places where you may need precision, but often not, in a large percentage of cases you're more interested in the trend rather than the absolute numbers.

For example I've often used the Maxim BS18B20 direct-to-digital temperature sensor. It looks for all the world like a BC547 but outputs its temperature with a resolution of one-sixteenth of a degree Celcius, but with an accuracy of half a degree between -10 and +85. Greater outside those limits. So you can see the trend even if you're not absolutely sure of the actual measurement.

In other words, how much accuracy is actually required?

Steve A.

Some years ago I met an American guy in my local pub. He was confounded by degrees Celcius in weather forecasting. I told him a simple rough rule-of-thumb...double the Celcius then add 30. It's near enough to know if it's going to be freezing, cold, cool, nice, warm, hot or ***** hot. An example where absolute accuracy isn't really required. If you can multiply Celcius by 1.8 and then add 32 in your head after a few beers, you're better than I!
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Re: NBTV for PMR446

Postby Klaas Robers » Thu Oct 29, 2020 7:06 am

Steve Anderson wrote:..... a simple rough rule-of-thumb...double the Celcius then add 30.

I never have realized that it can be that simple. I am going to remember that one.
Of course I was teached at my Dutch school:
- divide by 5
- multiply by 9
- add 32.
But that was in the Physics lessons. Physisists are no engineers, they hardly ever MAKE something, they only calculate with as many decimals as come.

I never understood why the Americans are still used to Fahrenheit. I think they are the only people in the world. In that respect: what is great again?
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