Ultrasonic flying spot scanner NBTV

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Postby Harry Dalek » Sun Sep 01, 2013 12:22 pm

gary wrote:I am afraid I can't have any sympathy with regards your iPhone Harry - I am not rich enough to have one... at least not rich enough to waste money on them. ;-)

You should us a Raspberry Pi! :-)

BTW, given that your transmitter is, I think?, an FM modulator - how is your receiver demodulating it?


Oh i don't like the iphone at all ! i just have a old flip one for use... have 2 old iphones spare that were dropped by the kids and wife is not happy with those any more so i made use of the thing what better than a nbtv player.


Yes also have to wear glasses for them to small for me for most stuff and most of the apps you have to pay for rather a windows version if there is such a thing.

Yes gary i think i have stuffed up here sstv is fm i am think both trans mitters are fm the PWM works that way and modulating to pin 5 of the timer i think does the same ...look into this more this afternoon.
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Postby Harry Dalek » Sun Sep 01, 2013 12:28 pm

Klaas Robers wrote:In principle you should use a signal centered around 40 kHz. That is the optimum working frequency of these transducers.


Yes with both transmitters i can adjust both frequencies works fine for slow scan television worked right away when i tried it !

So you should use a modulated carrier of 40 kHz, but then the bandwidth gives the next limitation. It is ± 1 kHz for these transducers, while NBTV needs a base band bandwidth of 10 kHz, that is ± 10kHz if you use AM (Amplitude modulation). For FM you need even more bandwidth.

It should have the enough bandwidth for nbtv if its doing slow scan but i think gary thinking about the fm and am difference of the 2 ?

Then you run into the next difficulty: reflections! With a sound frequency of 40 kHz all walls of a room and all furniture will reflect the sound. And as adjacent dots in an NBTV picture are travelling in the sound wave at a distance of just 1.5 cm apart, all reflections will mix up your received signal. Only abroad this may work, as there are no reflecting subjects, at least if you do your experiments in a desert or at the beach.

Good luck! You will need it.


Its a lot of fun trying i really want to try the reflecting the signal i could test all this now with slow scan but i want NBTV !!!!!! :roll:
Reflections causing a total mess of a scanning idea i was thinking it could do perhaps just shapes....against a wall may be just see how it gos just like to try simple transmitting before i try any thing else just ideas :idea:
Last edited by Harry Dalek on Wed Sep 04, 2013 9:53 pm, edited 1 time in total.
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Postby gary » Sun Sep 01, 2013 12:56 pm

Oh but Harry, Klaas is correct if the transducer only has a bandwidth of +/-1 kHz then you have no chance at all of transmitting NBTV (at least in terms of an NBTVA standard) - I'm all for experimenting but you have to start with some level of feasibility - it's like building your house with a doll's house sized front door on the chance it "might" be able to let people in...

A very crude NBTV picture of, say 16 lines and 4 frame per sec *might* be possible...

BUT! What is it you are *really* trying to do here? I admit I really haven't paid enough attention to that.

Are you trying to transmit standard NBTV ultrasonically? (implied by the fact you are FM modulating the 40kHz carrier) or are you trying to create some kind of ultrasound scanner? in which case there is no modulation of the source required - your circuits seem to have a foot in both camps. I am lost now.
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Postby Harry Dalek » Sun Sep 01, 2013 5:32 pm

gary wrote:Oh but Harry, Klaas is correct if the transducer only has a bandwidth of +/-1 kHz then you have no chance at all of transmitting NBTV (at least in terms of an NBTVA standard) - I'm all for experimenting but you have to start with some level of feasibility - it's like building your house with a doll's house sized front door on the chance it "might" be able to let people in...



Hi Gary back from fathers day vists ....i was thinking i might not be able to do it due to this with what the transducer can do . but why is then that an Fm signal which would be worse works ...it has no problems at all with the SSTV video at all that would be much more than a percentage either side of 40 khz ?
Now i didn't click about the AM FM difference ...i am trying to get my head around why 2 video systems which could be fitted in around the same bandwidth one works one doesn't .
I can hear the nbtv fine but something i did is wrong of cause .
I would say to bandwidth of the transducer for sure but it does does SSTV no problems at all i can tune it in and out of the correct receiving frequency of the transducer .

A very crude NBTV picture of, say 16 lines and 4 frame per sec *might* be possible...


I really don't know yet ....what do you think of the SSTV working ?

BUT! What is it you are *really* trying to do here? I admit I really haven't paid enough attention to that.


Well starting at the start really i have never played with these before and as you know one thing leads to another so starting with seeing if NBTV can be transmitted and received ,then i can go on to other ideas with it... if it can't theres no point ...

If all gos well i think a flying spot of ultrasound might be able to scan some shapes as in a flying spot scanner idea ..i would use 2 rotating shapes to bounce the sound off for the scanning that way theres no signal loss...big problem i can see is focusing but the beam is focused from what i have read with the shape of the transducer cones ... this is all up in the air ideas but i would like to try if things go well on the best case which would be a good signal transmitted between transducers .

Are you trying to transmit standard NBTV ultrasonically? (implied by the fact you are FM modulating the 40kHz carrier) or are you trying to create some kind of ultrasound scanner? in which case there is no modulation of the source required - your circuits seem to have a foot in both camps. I am lost now.


For a start transmitting then i know i have the bandwidth then i can move on to other ideas with it ...need to see a simple system working then you know you can try something harder is the way i look at it .
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Postby Harry Dalek » Sun Sep 01, 2013 7:43 pm

I just did the sweep test and a little video of SSTV transducer transmitting i will up load tonight just have to drop the video size a bit.
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Postby gary » Sun Sep 01, 2013 7:54 pm

i am trying to get my head around why 2 video systems which could be fitted in around the same bandwidth one works one doesn't .


Well that's not true - as far as I am aware SSTV does not normally exceed 3kHz and could feasibly be much lower, whereas 32 line 12.5 f/s NBTV requires 10kHz.

I can hear the nbtv fine but something i did is wrong of cause


Well yes you will hear the characteristic 400Hz NBTV sound as that is within the 1kHz bandwidth. Although how it is being demodulated is beyond me - I read somewhere that the nonlinearity of the US passing through air can actually demodulate it - weird.

I really don't know yet


I assume you say that because your approach is empirical rather than analytical - let me explain how I came up with those parameters:

The bandwidth required to transmit an nbtv signal of:

lines = n
aspect ratio = a
frame rate = fr

is given by:

bw = n*n*a*fr/2

so for NBTVA video bw = 32 * 32 * 1.5 * 12.5 / 2 = 9,600 Hz or 9.6 kHz (we normally call that 10kHz)

so for the parameters I gave you the bandwidth is:

16 * 16 * 1.5 * 4 / 2 = 768 Hz

Given that a narrowband FM signal bw is 2fm then 2 * 768Hz fits into the available bw of the transducer.


....what do you think of the SSTV working ?


The same formula above applies to sstv - now you know that a frame of sstv may take many seconds - lets say 10 seconds - so the frame rate is 1/10 = 0.1 frames per second.

Plug that into the formula above and you can see that the BW is very small indeed even for much higher resolution pictures.

Does that explain things?

Well starting at the start really i have never played with these before and as you know one thing leads to another so starting with seeing if NBTV can be transmitted and received ,then i can go on to other ideas with it... if it can't theres no point ...


I note that you don't define NBTV - if you don't define it I will always assume that it is NBTVA 32 line NBTV.

Well I can certainly assure you that NBTV CAN be transmitted ultrasonically providing the carrier wave can be modulated/demodulated appropriately and that the bandwidth of the transducer is sufficient.

So you have to make a decision to either reduce the resolution and frame rate of the NBTV signal, or find a transducer with a wider bandwidth - they must exist surely!??? I can't imagine they would be cheap though.

There is another, very complex alternative whereby you split the signal bandwidth over a number of transducers with different carrier frequencies - that would be fun! not!

Also you have to decide on the modulation scheme AM or FM - I would suggest AM as an FM demodulator is fairly complicated. Also you have the circuits available to you as you indicated.

As for the scanning... well you are pretty much on your own there - I see no end of physical problems no less than, as you mentioned, the focussing of the pressure wave without significant loss - my brain hurts thinking about it.

In addition, I should say there is no real similarity between transmitting an NBTV signal ultrasonically and scanning with ultrasound (other than the use of ultrasound). There is not much that you learn in the former that can be applied to the latter.

i would use 2 rotating shapes to bounce the sound off for the scanning that way theres no signal loss


Hmmm I am not sure I am following you there - there has to be signal loss or there would be no image - when scanning an object ultrasonically you are more or less measuring the density of the object under each "sound spot" - that is a hard non absorbing material will reflect the sound with far less attenuation than a soft absorbing material - you won't be able to use the piece of paper with NBTV written in large letters trick. ;-)

Finally, given the average age of the NBTVA membership I am not entirely sure that your "ultrasonic" transducer couldn't just be a reasonably good quality speaker. For instance here is a full NBTVA BW sweep modulated up to 13kHz - I can just barely hear the low frequencies.
Attachments
ultrasonic.wav
Ultrasound for the mature person
(937.56 KiB) Downloaded 234 times
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Postby Harry Dalek » Sun Sep 01, 2013 9:03 pm

Heres the sstv and sweep tests ...as per normal had to do them quick while the kids were busy :shock:

I am using my hand to reflect the ultra sound much better pointing the things at each other .
Attachments
P1050712.avi
ultrasound sstv reflecting off my hand
(6.32 MiB) Downloaded 248 times
1 00001.jpg
transmit test
1 00001.jpg (193.57 KiB) Viewed 5625 times
sweep 1hZ-10kHzand bit of nbtv1.wav
This one should work gary sweep test
(1.41 MiB) Downloaded 229 times
Last edited by Harry Dalek on Sun Sep 01, 2013 9:54 pm, edited 1 time in total.
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Postby gary » Sun Sep 01, 2013 9:11 pm

Harry the sweep wave file is just 15 seconds of silence - something has gone wrong there I think.

BTW can you post the SSTV signal please?

What app are you using to display it?
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Postby Harry Dalek » Sun Sep 01, 2013 10:04 pm

gary wrote:Harry the sweep wave file is just 15 seconds of silence - something has gone wrong there I think.

Sorry about that i checked and yes didn't save right, i did 3 so see if the re uploaded one works it works this end .


BTW can you post the SSTV signal please?


I didn't think of that i will tomorrow...but the sound via the video is the received sstv out of the laptop

What app are you using to display it?


What i did is my iphone has wifi so youtubed classic sstv used that sound fed to the transmitter ...the receiver is connected to the laptop ...using MMSSTV to view the 8ec B/w in auto mode ...
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Postby gary » Sun Sep 01, 2013 11:03 pm

Well it would appear your NBTV is inverted. The bandwidth is severely limited but it's hard to tell exactly because of the high level of distortion. However I seem to be able to see the number 2 and perhaps 12.

The sweep is there but heavily distorted and full of harmonics.

The SSTV will show something with a band limited signal BUT are you SURE that the laptop is picking up the demodulated US and NOT the base band signal from it's microphone? Given the reduced bandwidth AND the high level of distortion it's hard to see how it could produce a picture at all.
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bit of nbtv1.avi
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Postby Harry Dalek » Sun Sep 01, 2013 11:24 pm

gary wrote:Well that's not true - as far as I am aware SSTV does not normally exceed 3kHz and could feasibly be much lower, whereas 32 line 12.5 f/s NBTV requires 10kHz.


I stand corrected there must be a little bit of difference between the many different modes well thats the case i will look more closely at the transducers but i think i should not blame them just yet as theres a bit of Harry electronics between so i know who i'd blame first .... 8) !



Well yes you will hear the characteristic 400Hz NBTV sound as that is within the 1kHz bandwidth. Although how it is being demodulated is beyond me - I read somewhere that the nonlinearity of the US passing through air can actually demodulate it - weird.


I don't see the sync that well on your software scopes but yes hearing it means little and really does so far trying to view it i see no hint of shapes out lines ,i was just thinking the sync was not making it .

I assume you say that because your approach is empirical rather than analytical - let me explain how I came up with those parameters:


OK my little 1980s xt processor in my head will try :oops:

The bandwidth required to transmit an nbtv signal of:

lines = n
aspect ratio = a
frame rate = fr

is given by:

bw = n*n*a*fr/2

so for NBTVA video bw = 32 * 32 * 1.5 * 12.5 / 2 = 9,600 Hz or 9.6 kHz (we normally call that 10kHz)

so for the parameters I gave you the bandwidth is:

16 * 16 * 1.5 * 4 / 2 = 768 Hz

Given that a narrowband FM signal bw is 2fm then 2 * 768Hz fits into the available bw of the transducer.


Oh i am glad you did that i would have no hope ...but i understand now the sstv fm is narrower than the NBTV.



The same formula above applies to sstv - now you know that a frame of sstv may take many seconds - lets say 10 seconds - so the frame rate is 1/10 = 0.1 frames per second.

Plug that into the formula above and you can see that the BW is very small indeed even for much higher resolution pictures.

Does that explain things?


Yes sir i can see they are not the same so its not so much a mystery due to them not using the same bandwidth .
But i will try a bit more as i said need to make sure its not the harry factor more than the transducers .

I note that you don't define NBTV - if you don't define it I will always assume that it is NBTVA 32 line NBTV.


Well yes 32 line standard .


Well I can certainly assure you that NBTV CAN be transmitted ultrasonically providing the carrier wave can be modulated/demodulated appropriately and that the bandwidth of the transducer is sufficient.


Yes my reasoning for trying Just using what i had handy ,i want to try to do it as it has my interest at the moment .

So you have to make a decision to either reduce the resolution and frame rate of the NBTV signal, or find a transducer with a wider bandwidth - they must exist surely!??? I can't imagine they would be cheap though.


I will look into that i have read of tweaters being used they are at about 2khz to 20khz perhaps that might be a better idea for this ..some thing to look into .

There is another, very complex alternative whereby you split the signal bandwidth over a number of transducers with different carrier frequencies - that would be fun! not!


Not fun ... but speakers and tweeters are used together for the same sort of idea one device has a frequency bandwidth they can put out and the other does what the other can't ...

Also you have to decide on the modulation scheme AM or FM - I would suggest AM as an FM demodulator is fairly complicated. Also you have the circuits available to you as you indicated.


Heres the thing i don't have a Fm demodulator for the sstv i would of thought it was a no goer as is but it works for Fm...but it must be doing it .
the receiver should be a Am receiver ... the transmitters are FM...i did try a little am modulation of the carrier on my first transmitter and i did get a result i was thinking it might have been stray RF the receiver was picking up but i need to redo the experiment .

As for the scanning... well you are pretty much on your own there - I see no end of physical problems no less than, as you mentioned, the focussing of the pressure wave without significant loss - my brain hurts thinking about it.


Oh yes...i think they use banks of transducers for sonar and ultrasound imaging i would not expect great results perhaps seeing shapes perhaps...... and you would be doing it blind really ...focusing and all.
I enjoy trying stuff even if i fail.

In addition, I should say there is no real similarity between transmitting an NBTV signal ultrasonically and scanning with ultrasound (other than the use of ultrasound). There is not much that you learn in the former that can be applied to the latter.


Its just an idea to try if things fall into place turn sound into light more than likely a poor version of a ultra sound in air but just an idea so far but who knows .


Hmmm I am not sure I am following you there - there has to be signal loss or there would be no image - when scanning an object ultrasonically you are more or less measuring the density of the object under each "sound spot" - that is a hard non absorbing material will reflect the sound with far less attenuation than a soft absorbing material - you won't be able to use the piece of paper with NBTV written in large letters trick. ;-)



Sorry gary when i had the idea it was point a transducer at a nipkow and do a sort of sound flying spot camera but i can see a lot of signal loss more than likely it would not work at all...... rather nothing in its way i was thinking perhaps a pointing the transducer at a polygon shape rotating sort of like my laser nbtv octagon project a while back and do a sort of sound version instead of mirrors just a flat reflecting surface for the sound to bounce off.

Have the receiver and transducer near the object being scanned just a sound fly spot scanner idea really...works in my head but thats my head OMG !

Finally, given the average age of the NBTVA membership I am not entirely sure that your "ultrasonic" transducer couldn't just be a reasonably good quality speaker. For instance here is a full NBTVA BW sweep modulated up to 13kHz - I can just barely hear the low frequencies.


I can hear one fourth of it rest is beyond my big ears ! :shock:
Last edited by Harry Dalek on Mon Sep 02, 2013 12:03 am, edited 1 time in total.
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Postby Harry Dalek » Sun Sep 01, 2013 11:50 pm

gary wrote:Well it would appear your NBTV is inverted. The bandwidth is severely limited but it's hard to tell exactly because of the high level of distortion. However I seem to be able to see the number 2 and perhaps 12.


I have the transducer for the transmitter and an NPN trany emitter driving it .
The avi i see that at times on your viewers could not really tell what it was or close to what it should be ..

Perhaps i should do a transmitted signal and the wav if came from it might be more helpful .



The sweep is there but heavily distorted and full of harmonics.


This is the PWM version mixing the sound and oscillator in a lm311

The SSTV will show something with a band limited signal BUT are you SURE that the laptop is picking up the demodulated US and NOT the base band signal from it's microphone? Given the reduced bandwidth AND the high level of distortion it's hard to see how it could produce a picture at all.


If you are talking lap top mic theres no sound from the receivers speaker thats off ...perhaps i should try it with no speaker sound from the laptop ....or is there an experiment you think i need to try to make sure or you need to see ?
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Postby Klaas Robers » Mon Sep 02, 2013 12:19 am

Gary,

SSTV is a video signal with a video bandwidth of 1 kHz. The signal is modulated onto a carrier with a frequency sweep of 900 Hz peak-peak. That gives a Carson bandwidth of 2900 Hz, normally from 300 to 3200 Hz, just fitting the telephone bandwidth.

This FM signal is what commonly is called the SSTV signal. If you limit that somewhat, e.g 400 to 2800 Hz that will fit into the 2.4 kHz SSB bandwidth and is still demodulatable, although no more without AM. If this FM signal is shifted to the 40 kHz centre frequency of the US transducers, it will still work, with some more AM, but who cares.

The real difference is that the video bandwidth of NBTV is 10 kHz and of SSTV is 1 kHz. That factor of 10 is far to much to neglect.

Oh yes, SSTV is 120 x 120 pixels with a frame duration of 7.2 seconds.
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Postby Harry Dalek » Mon Sep 02, 2013 5:34 pm

Klaas Robers wrote:Gary,

SSTV is a video signal with a video bandwidth of 1 kHz. The signal is modulated onto a carrier with a frequency sweep of 900 Hz peak-peak. That gives a Carson bandwidth of 2900 Hz, normally from 300 to 3200 Hz, just fitting the telephone bandwidth.

This FM signal is what commonly is called the SSTV signal. If you limit that somewhat, e.g 400 to 2800 Hz that will fit into the 2.4 kHz SSB bandwidth and is still demodulatable, although no more without AM. If this FM signal is shifted to the 40 kHz centre frequency of the US transducers, it will still work, with some more AM, but who cares

The real difference is that the video bandwidth of NBTV is 10 kHz and of SSTV is 1 kHz. That factor of 10 is far to much to neglect.

Oh yes, SSTV is 120 x 120 pixels with a frame duration of 7.2 seconds.


Thank you very much Klaas and Gary for once again some very good answers and advice .

This Answers the bandwidth Question pretty much still would like to make sure with one last sweep test which i have been thinking about using the laptop sound card to transducer or iphone i think that will work to test the bandwidth of the receiving transducer that way theres no messy transmitter in the way my receiver sounds pretty clean on its own ...my problem is the sound card can i think only do to 20 or so khz perhaps it will show nothing or a rise as the frequency increases.....least with testing i will know what to use .

In any case( it sounds like forgive the pun ) i need some thing with more bandwidth perhaps a tweeter look into what the other transducers from old jaycar sells never know ....

I will try and do some tests to make sure what i use has the 10khz band width...
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Postby Harry Dalek » Mon Sep 02, 2013 11:42 pm

I tried some thing different today again using the i phone as a Player with its speaker and the laptop as a recorder ...with a crystal earphone as the mic ..

This was at close range just to test speaker and mic ...I had only a little time
so i would of liked to feed the i phone into a tweeter still not great results for NBTV via its speaker but again SSTV worked fine .

So seeing is believing these have a greater bandwidth to work with but i have a feeling the i phones speaker is to blame for the still poor NBTV results .

I have done sweep test and a nbtv test and a sstv test i will upload here...

Well had to take a few steps back might be to go forward :roll:

BTW i looked into jaycars wide band transducers under 4khz band width those are 50 bucks yakes @ ! and still to narrow .

EDIT
I came across this Piezo-electric transducer detuning it seems to increase the bandwidth of a transducer its gives the wanted 10khz bandwidth don't know if it would work with mine .
http://bertrik.sikken.nl/bat/detuning.htm
Attachments
earplug 150 pixels.jpg
Used this as the mic
earplug 150 pixels.jpg (7.95 KiB) Viewed 5571 times
crystalmic.wav
Heres the sweep test crystal mic i phone speaker
(853.8 KiB) Downloaded 226 times
crystalmicsstv.wav
Heres the sstv test ....works fine if you can find some thing to play it ....
(9.51 MiB) Downloaded 232 times
crystalmicnbtv.wav
NBTV via the mic and speaker
(758.2 KiB) Downloaded 223 times
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