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Lowtone wrote:Ah yes the "it doesn't work" is a way to speak, i don't mean the softwares are themselves faulty, this can come from anywhere else, especially i'm getting back to NBTV but it's been a few years that i was away, so i forgot how to use the softwares.
I can have ideas, but i'm not an electronician, mathematician or programmer. I happened to be here because i like the History of télévision ( and related techniques ) and the technical things.
My message was not very detailed, i'm sorry
Lowtone wrote:There was two files, one shortwave, and one standard format.
Both sent on PMR446 ( NFM ) a few metres aways. ( this radio is only able to NFM and FM formats, no WFM/AM/SSB )
Lowtone wrote:There was only two concrete walls until the receptor
There was a few ( quite few ) disturbances during the transmition ( to see what can happen )
I put a portable digital recorder near the receptor
i took the file from this, ( direct transfert, no analog line-in step )
some parts are raw, and i filtered some others ( to remove noise that is out of the bandwith )
I splitted this in two separate files for both formats ( so that got some stability in NBSC was the NBTVA one )
There cannot be left and right inversion, because the same signal is on both tracks
Lowtone wrote:I haven't checked the phase inversion
Lowtone wrote:Why do this format don't use sync pulses ?
gary wrote:I also realise that English is not your first language and translating all the time must be a pain and make you want to be as brief as possible, I do appreciate you going to that trouble.
gary wrote:Aaah, now I am not all that familiar with narrow band fm although it seems it is just a narrow band version of FM.
gary wrote:This attempt was moderately successful: https://www.youtube.com/watch?v=TGgmCiJ9iEM
gary wrote:Certainly the channel bandwidth of the PMR446 is wide enough (especially FM) - but I wonder about it's phase linearity? That is relatively unimportant for audio but not for video.
gary wrote:Because the (important) frequency components of a sync pulse are very low and mostly outside of the frequency range of typical audio and hence is high pass filtered out anyway.
gary wrote: for Amateur Radio channels syncs have proved to be more trouble than they are worth.
gary wrote:this is why the sample rate of the CLS is 48 kHz - that is the native sample rate of most codecs in a sound card and is an integer multiple of the xtal oscillator on the card and therefore quite (but not perfectly) accurate
gary wrote:I would appreciate it very much if you could post the unfiltered CLS wave file you recorded - if nothing else I would be very interested in having a look at it.
Lowtone wrote:Oh it was mostly because i was also doing something else. Language was not the problem, i was just giving up and switching to another activity.
I don't transalte, i just try to think in English. But in France language lessons are not very good, so expect from me only limited vocabulary and simple sentences.
Lowtone wrote:I don't know either, plus there is the whole line of it.
One computer was reading my file, then the signal gone towards radio with a cable, but for the receptor we need to take account of the linearity of the speaker, and the one for the recorder's microphones. Errors can cumulate.
Lowtone wrote:Could it be possible to make a kind of "inverted" synch pulse, or put it in a place where it is not erased ?
the SSTV sync system is interesting, it's an 1200 Hz beep wich is steady, and remains way under the signals
Lowtone wrote:It's only good for CD.
gary wrote:I would appreciate it very much if you could post the unfiltered CLS wave file you recorded - if nothing else I would be very interested in having a look at it.
Lowtone wrote:Unfortunatly i ditched the original file, but in both files there are filtered and non filtered parts, spetrograph can reveals this clearly
gary wrote:Well I wish my French was a fraction as good as your English.
gary wrote:Aaaah I didn't realise you were interfacing to the receiver via loudspeaker and mic, that will introduce a lot of variability - although it doesn't explain the results you were getting (at least as far as your .png file indicated). That was indicative of loss of sync as some of the lines appear to be offset against the main picture and as there ARE no syncs that is very strange unless that picture was from your NBTVA format experiment, in which case it isn't surprising at all.
gary wrote:I suppose the transmission frequency you are using doesn't give many options in terms of what receivers you can use (i.e. one with an earphone socket).
gary wrote:Besides all that, syncs are just not needed. Baird didn't use them.
gary wrote:(and don't forget this stuff is intended to be used as a source for a mechanical monitor).
gary wrote:Not even that - the worst technical decision ever made IMHO - all (or mostly) to be compatible with the line and frame rates of PAL and NTSC television - WTF?
gary wrote: I assume that you had no problems playing the test video nbtvbaird-chrislong-sw.wav directly on TBP and that you only had a problem when it came from the radio?
gary wrote:NBTVer is ME! That was a test performed between Vic Brown and I think Peter Smith using Vic Brown's VSB system - I had been helping out with some software based filters and this was a results sample he sent me. I think I did some time base correction on it prior to posting, I can't remember for sure. You can clearly see there that trying to pick sync pulses out of all that noise would somewhat problematical - that is an example of syncless transmission over quite a distance.
gary wrote: Unlike audio I don't think there are any "unimportant" frequencies in the video spectrum however.
gary wrote: low amplitude frequency regions that could be discarded without substantial loss - trading some contrast for better frequency response.
gary wrote:I think your idea of the first pixels being white is an excellent idea, alas for you, it is not original - Baird himself used the technique (albeit black) -
gary wrote:and has been replicated many times in both black and white - it doesn't really matter if it is black or white the main problem is that if the scene becomes black or white then you lose sync -
gary wrote: thus for early television experimental transmissions black was not allowed!
gary wrote:You still seem to be determined to find a way to get synchronisation pulses into the video signal and I am wondering why?
Lowtone wrote:We may disagree on this, since i'm a musician and i also like to mix multitrack recordings. I can be picky on this
But i got your point
Lowtone wrote:ah ^^ black on the first line, intersting, so it was only a frame pulse, no pulses on the other lines ?
Lowtone wrote:So the sync is always lost ?
I thought that since the other pulses are blacker-than-black, a white one would made a very high contrast and cannot be misinterpreted as a line pulse.
Lowtone wrote:Because i remind having troubles with the MUTR to keep sync. And also, if the software can add/restaure pulses it will be compatible with the NBTVA standard.
I like to keep doing all the production line in one format. But well if it's not necessary…
gary wrote:Ok, I had trouble following your argument, so you have white pixels instead of a "missing pulse" in conjunction with blacker-than-black sync pulses?
gary wrote: In that case I would suggest that you would almost always miss the next line sync or 2 because the white has driven the average signal level above the sync slice - if I get time I will create a bit of software to demonstrate what I mean.
gary wrote:Sync will only be lost if some part of the signal "looks" like a frame pulse but isn't - with a very noisy signal that can happen any time.
gary wrote:I see. But, of course, the signal does not need to have HAD syncs in it to have syncs added - they can be added any time either in software or hardware.
Lowtone wrote:So it must he hard contrast picture. Maybe putting a white horizontal line above the sync can create a good contrast
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