Colour NBTV over ultrasonic sound

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Colour NBTV over ultrasonic sound

Postby Panrock » Mon Oct 14, 2019 2:06 am

It's been a while since I've posted here. I've been very tied up with the project to get licensed 405-line TV back on the air again in the UK. The vision and sound transmitters are complete at last and attention is now being directed to building the transmitting aerial. Anyway, I digress...

I have in my possession a mechanical 30-line colour monitor that I built many years ago - the "Grosvenor" (since converted to horizontal scanning to take advantage of the 30-line standards available from my WC-01 converter) and what was once a matching mechanical colour camera, using R,G, and B photomultipliers. This camera will now also have to be converted to horizontal scanning.

Wiring up multiway RGB cables between the two units is such a fag... so what I would like to do is convey the colour pictures from the camera to the monitor over a modulated ultrasonic sound link... say 40kHz. Do you think this will be possible? I guess getting sufficient bandwidth out of (resonant) transducers will be a problem. Maybe I can use a higher carrier frequency with a piezo crystal? Which club colour encoding/decoding standard should I use? Remember I want to stick to 30-lines horizontal (because I have an excellent pair of disks that give a large bright square picture) and not change to 32-line vertical.

Thanks for any help received. :)

Steve O
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Re: Colour NBTV over ultrasonic sound

Postby Harry Dalek » Mon Oct 14, 2019 5:54 pm

Panrock wrote:It's been a while since I've posted here. I've been very tied up with the project to get licensed 405-line TV back on the air again in the UK. The vision and sound transmitters are complete at last and attention is now being directed to building the transmitting aerial. Anyway, I digress...

I have in my possession a mechanical 30-line colour monitor that I built many years ago - the "Grosvenor" (since converted to horizontal scanning to take advantage of the 30-line standards available from my WC-01 converter) and what was once a matching mechanical colour camera, using R,G, and B photomultipliers. This camera will now also have to be converted to horizontal scanning.

Wiring up multiway RGB cables between the two units is such a fag... so what I would like to do is convey the colour pictures from the camera to the monitor over a modulated ultrasonic sound link... say 40kHz. Do you think this will be possible? I guess getting sufficient bandwidth out of (resonant) transducers will be a problem. Maybe I can use a higher carrier frequency with a piezo crystal? Which club colour encoding/decoding standard should I use? Remember I want to stick to 30-lines horizontal (because I have an excellent pair of disks that give a large bright square picture) and not change to 32-line vertical.

Thanks for any help received. :)

Steve O


I looked into this with air transmitting with normal speakers mics have the bandwidth but transmitting via air is very poor ! even nearly touching ...reason i tried a different medium liquid as you know works well ...
I too looked into ultrasonic's but most transducers don't have a wide enough bandwidth you would be lucky to do a narrow band version of SSTV .i have BTW done this and works you can bounce the video signal off your hand to the receiver transducer .
There are pricey Transducers with the bandwidth when i was looking ..may be modulated on a carrier as you are thinking would work ...but normal ones are useless with a 1khz bandwidth .
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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Re: Colour NBTV over ultrasonic sound

Postby Panrock » Mon Oct 14, 2019 7:04 pm

Thanks Harry... I should have known you had been here first. :D

Maybe try a flat piezo crystal with an air-matching horn? Or even just a standard 'tweeter'?

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Re: Colour NBTV over ultrasonic sound

Postby Harry Dalek » Mon Oct 14, 2019 9:17 pm

Panrock wrote:Thanks Harry... I should have known you had been here first. :D

Maybe try a flat piezo crystal with an air-matching horn? Or even just a standard 'tweeter'?

Steve O



Hi again Steve
viewtopic.php?f=1&t=1730&hilit=ultra+sonic&start=15

You can see a pic of my Ultrasonc SSTV transmitting idea sound bouncing off hand ..forgot all about that till reading your post ...

Air is very poor for sound waves thicker the gas the better i would think if you have fog ? that might work much better !.... some way of focusing passive amplifier dish horn may help i never tried that ...what got me was the tweeter and mic had the bandwidth i just could not understand why even very close range the result was poor ....as we now know it was just the air ..may be more amplification might over come this ? or just modulating it on a carrier high frequencies are least 10khz should be possible with a tweeter...that would be the way to go i think ....colour transmitting you are thinking about is a first so hope you get it going like to see it ...thinking of something similar to this for my record lathe...BTW second page will be of interest more what your thinking
viewtopic.php?f=1&t=1730&hilit=ultra+sonic&start=30
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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Re: Colour NBTV over ultrasonic sound

Postby Klaas Robers » Mon Oct 14, 2019 11:43 pm

I don't know....

1. What is commonly known is that lower tones are audible over a longer distance. If you listen to a brass band walking on the street and coming in your direction, you first hear the lowest tones, the large drum. And when they are coming closer, you start to hear the higher tones, the better and the higher the closer they come. So really high tones in sound look to be a bad idea.

However....

2. I have seen a set-up of two large steel parabolic mirrors, say 5 metres in diameter, about 300 metres apart in the open air, "looking" to each other. In the focus point you can position your mouth or your ear and you can communicate to someone else on a whispering level, over 300 metres. I tried this of course and it struck me that there was no high tone roll off audible.

3. The Philips dome tweeters are fine to at least 20 kHz and I guess a few tens of kHz more. But do not send more than 1 watt to them or they will die. The small electret microphones that you found built into cassette recorders, don't have problems with these high tones either.

4. The problem of sound in a room is reflections against the walls and all other solid objects in the room. 20 kHz has a wave length of no more than 17 mm, so reflections in the room will spoil your accoustical signal. The dome tweeter is constructed to give minimal directivity, and the electret has a diametre of less than 1 cm, so the directivity is also small. Ergo: the reflections are giving you problems.
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Re: Colour NBTV over ultrasonic sound

Postby Panrock » Tue Oct 15, 2019 1:36 am

Thanks for your opinion, Klaas.

Klaas Robers wrote: The small electret microphones that you found built into cassette recorders, don't have problems with these high tones either.

Yes, I have built a Maplin kit using such a mic, for listening to ultrasound from bats, jangling keys, etc. It has a tuning control from 20 to 160 kHz!

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Re: Colour NBTV over ultrasonic sound

Postby Steve Anderson » Tue Oct 15, 2019 1:21 pm

All the above is what I've found. Reflections off any object will either add or subtract from the received signal depending on the relative path lengths. i.e. the relative phase and amplitude of the reflected signal verses the direct signal at the receiver. In a room there are going to be many reflections, if any reflecting (or absorbing) object moves (you) the received signal level varies. Those old enough will remember the 'aircraft flutter' on analogue TV, especially 405-lines, aircraft that are airborne have a habit of moving! Same idea, just acoustics rather than RF.

I suggest going to optical, preferably visible (makes aiming easier). Assuming the Grosvenor still uses the PWM method, move the PVM generators to the 'transmit' end, modulate the LEDs/Luxions/whatever with that (ON/OFF). That's fine for a single monochrome channel, for colour it's going to be a tad more complex, adding sound adds to that.

Steve A.

Are 3/4/5 cables to plug up that onerous? (RGB + Syncs + Audio). You could use a D-type at each end with a single multicore/multipair cable to carry all. Then you wouldn't have to move the PWM generators at all. Probably the simplest arrangement.
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Re: Colour NBTV over ultrasonic sound

Postby Panrock » Wed Oct 16, 2019 12:47 am

Hello Steve A.

As regards using sound as the transmission method, the lesson coming back loud and clear is that multipath will be a problem. What about using something as simple as an electret mic down the bottom end of a cardboard tube? This would exclude anything but the direct hf sound signal. At the transmit end, we might see the sound from a tweeter fanning out to be collected and reflected by a large kitchen mixing bowl (say)….

If I'm looking for an efficient, elegant, solution - you are undoubtedly right about optical. Your excellent PWM drivers would do the job. But I am being perverse here and would like to try sound, which I've no experience of. Also, light links in practice need very accurate pointing and alignment.

Something that has been rather 'hushed up' is that my demonstration of PAL colour and sound on a VHF channel over light at the last Convention was very nearly an abject failure. I had it working across the hall to start, though with a rather noisy picture, so then decided to move the receiving lens unit a little closer to the source. After I'd done this, I couldn't for the life of me find the beam again! :oops: The various members were going through their presentations one by one, and mine was getting closer - but I knew I'd have nothing to show! Fortunately, at the last minute David Gentle (bless 'im) gave my pickup lens a little nudge and hey presto - a good colour picture suddenly appeared on the screen!

I now feel sound would be a little less exacting!

You are right about D-Types. Indeed, I am using these for the data connections for the various protection systems on the 405-line transmitter. What I used on the Grosvenor and its huge accompanying camera were 'orrible fiddly DINs....

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Re: Colour NBTV over ultrasonic sound

Postby Steve Anderson » Wed Oct 16, 2019 11:21 am

Panrock wrote:You are right about D-Types. Indeed, I am using these for the data connections for the various protection systems on the 405-line transmitter. What I used on the Grosvenor and its huge accompanying camera were 'orrible fiddly DINs....

Urrgghh! DINs - One of the worst (if not THE worst) connectors ever devised! Up there on a par with the RJ45 (PC network connector), again ghastly - but the whole world now hangs on them.

Steve A.

...add the SCART connector too - I'm not sure which one of those three is the worst. Shame two of them are European. but thankfully never seen anymore...they never really made it outside Europe anyway.
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