Camera-monitor assembly and ssb transmission

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Camera-monitor assembly and ssb transmission

Postby sv3ora » Wed Jul 06, 2016 6:35 pm

Hello there, this is my first post here.

1. As a ham, I am interested in transmitting 30 or 32 lines of nbtv on HF and I wonder if this can be done on SSB (~3KHz)?
I have successfully used the programs in this page http://users.tpg.com.au/users/gmillard/nbtv/nbtv.htm to transmit video through sound card, on two separate PCs but I wonder how much bandwidth is really needed.

2. This page http://www.nbtv.wyenet.co.uk/cam-mon.htm describes a special disc that can be used for both transmitting and receiving. Has anyone got the disc pattern, so I can make my own disc? I would like to make a simple but standalone video "transceiver".

Thanks a lot.
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Re: Camera-monitor assembly and ssb transmission

Postby Steve Anderson » Wed Jul 06, 2016 8:09 pm

Hi, and welcome to the forum.

Normally the required audio bandwidth for NBTV is around 10kHz, but others have succeeded with less. I really have to leave it up to the guys with licences for this...

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Re: Camera-monitor assembly and ssb transmission

Postby gary » Wed Jul 06, 2016 8:41 pm

There are 2 formats available for shortwave transmission using Video2NBTV - the Chris Long shortwave format and the Vic Brown.

Some examples of shortwave transmission:
https://www.youtube.com/watch?v=7klqrR3TAoQ
https://www.youtube.com/watch?v=Sc759yJrNIU

You can download nipkow.exe from here to create any nipkow arrangement you desire:

http://users.tpg.com.au/users/gmillard/ ... Nipkow.zip
Perfecting an NBTV system is like trying to slam a revolving door...
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Re: Camera-monitor assembly and ssb transmission

Postby sv3ora » Wed Jul 06, 2016 9:43 pm

gary wrote:There are 2 formats available for shortwave transmission using Video2NBTV - the Chris Long shortwave format and the Vic Brown.

Some examples of shortwave transmission:
https://www.youtube.com/watch?v=7klqrR3TAoQ
https://www.youtube.com/watch?v=Sc759yJrNIU

You can download nipkow.exe from here to create any nipkow arrangement you desire:

http://users.tpg.com.au/users/gmillard/ ... Nipkow.zip

Thanks very much for the videos!
So it is done in 6KHz, which is typical for AM broadcasting. I have read in the NBTV site that it can be done in VSB as well, so I guess it can be done ok in DSB as well. After all DSB consumes the same bandwidth as AM, but DSB is better in terms of efficiency. Interesting...

I have seen this software before, but what setting do I need to play with in the "disk and hub properties", to create the double spiral arrangement that is mentioned in the NBTV site?

Thanks a lot!
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Re: Camera-monitor assembly and ssb transmission

Postby sv3ora » Wed Jul 06, 2016 9:56 pm

About the software, I fugured out the thing.

From the club disk description:
"The club disc has a spiral of 48 holes over 1½ revolution. The camera masks the inner 16, the monitor the outer 16 holes. In this way camera and monitor share the same disc. There is an extra circle of 32 sync-holes at the rim."

But what are the settings so that my disk will be "compatible" to the club's disks or standards used today?
I am thinking to build a smaller disk, but I suspect the ratios would only change.
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Re: Camera-monitor assembly and ssb transmission

Postby Klaas Robers » Wed Jul 06, 2016 10:34 pm

Indeed, the bandbidth of the video signal is about 10 kHz. The SSB bandwidth of 2,4 kHz is too low for it.
However, J.L. Baird did transmit 30 line video in AM modulation of the BBC Medium Wave transmitters. In theory the Low Frequency bandwith for MW is 5 kHz and the radio bandwidth 10 kHz, but the transmissions were after 12 mid night, so it is possible that the real HF bandwidth was larger at those times. With a smaller bandwidth only the sharpness is somewhat less.

Vic Brown G3SDQ transmits at a slower rate, 8.33 frames per second to lower the video bandwidth to 5 kHz and sends in vestigial side band. This still occupies a bandwidth of 6 kHz and you need a special VSB receiver for reception. This is shown in Newsletter 37/4. In 38/4 there is a report of results of some tests on 5 MHz.

In Newsletter 38/1 he explains why SSB with a suppressed carier is unsuitable for NBTV transmissions. This is mainly because video signals go down to DC. Then you NEED the carrier, or at least restore the carrier in the true phase.

So no real solution yet. However on VHF and UHF, and even at 10m, it is very well possible to transmit in AM. The 25 kHz bandwidth is there no point. 73, PAØKLS
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Re: Camera-monitor assembly and ssb transmission

Postby gary » Wed Jul 06, 2016 11:09 pm

Klaas Robers wrote:This is mainly because video signals go down to DC.


I discussed this with Vic and I am far from convinced that the bandwidth need go down to DC if sync is not used. For NBTV over shortwave I am not convinced that a sync or black reference is really necessary since noise and propagation phase distortion are far more serious a problem than frame alignment and contrast which can be easily adjusted for manually.

I say this in the context that any recognisable picture over an amateur AM 3kHz channel is a natural near miracle.
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Re: Camera-monitor assembly and ssb transmission

Postby sv3ora » Wed Jul 06, 2016 11:26 pm

gary wrote:I say this in the context that any recognisable picture over an amateur AM 3kHz channel is a natural near miracle.

Of course you refer to the analogue 12fps nbtv, because digital is another thing, see here for example http://www.qsl.net/zl1bpu/NBTV/RX.htm but B/W can only be transmitted at 1-2fps or so, not really a live video.

For only 6-10KHz it is amazing what can be done with 30-32 lines nbtv.
I agree totally, that the sync pulse might be a luxury on HF and it is probably going to create more problems syncing the lines than solve, due to the increased noise levels.
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Re: Camera-monitor assembly and ssb transmission

Postby gary » Thu Jul 07, 2016 12:23 pm

sv3ora wrote:
gary wrote:I say this in the context that any recognisable picture over an amateur AM 3kHz channel is a natural near miracle.

Of course you refer to the analogue 12fps nbtv, because digital is another thing, see here for example http://www.qsl.net/zl1bpu/NBTV/RX.htm but B/W can only be transmitted at 1-2fps or so, not really a live video.

For only 6-10KHz it is amazing what can be done with 30-32 lines nbtv.
I agree totally, that the sync pulse might be a luxury on HF and it is probably going to create more problems syncing the lines than solve, due to the increased noise levels.


I certainly refer to analogue, although for shortwave the fps is normally greatly reduced - this is acceptable when reproducing the signal digitally as on a computer say, as the objectionable flicker is eliminated.

Digital, unfortunately has even greater bw even when using compression, due to Nyquist, error correction etc. and the propagation path distortion of shortwave bands makes using digital somewhat difficult. There is room for development there though I think.

I regard the tx on NBTV a "miracle" though, not because of the limited bandwidth (which is problematic enough) but because of the horrifically low signal to noise ratio and propagation/phasing distortion of amateur bands. None-the-less Vic's VSB system seems to give markedly improved results.
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Re: Camera-monitor assembly and ssb transmission

Postby sv3ora » Thu Jul 07, 2016 6:01 pm

gary wrote:I regard the tx on NBTV a "miracle" though, not because of the limited bandwidth (which is problematic enough) but because of the horrifically low signal to noise ratio and propagation/phasing distortion of amateur bands. None-the-less Vic's VSB system seems to give markedly improved results.


I cannot find technical information on the VIC's VSB system, such as the frequency it operated, but VSB like DSB has the problem that two VSB rigs cannot communicate directly, since the two sidebands will present as the receiving frequency in the receiver. Only an SSB can distinguish the signal transmitted from a VSB station.

Anyway, here is another idea that came to my mind.
What if one could modify feld hell, for the purpose of nbtv?
In hell, the image is scanned and printed dot by dot in a line, just like nbtv.
The problem of synchronization could be fixed by the sync pulse, or without a sync pulse, by manual adjustments on the RX.
The only real problem I see is that the frame rate must be more limited and the fact that instead of two levels (on/off) we have to find a way to present the different brightness levels.
In hell, this can be done by limiting the signal strength, but the system would not be in fact a pure on/of but an AM with clearly defined power levels.
Just an idea...
By the way, fldigi using feld hell x5 gives a distinguishable BW image and I guess it is about 0.5fps, and the bandwidth is only about 1.2KHz judging from the waterfall, not a real time video though but not very bad for that bandwidth.
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