Klaas Robers wrote:Harry,
before you are going to try to record NBTV, first try to record a square wave signal. If you listen at the replay, you hear almost the same sound as when you listen at the original wave form. But if you look at your oscilloscope to the replay signal, you will not recognize the square wave of the input signal.
This happens because the lower frequencies are recorded deeper in the tape and at some distance from the gap in the recording head. The higher frequencies are recorded on the surface of the tape and right under the gap. What you will see is that the recorded square wave plays back as a more or less triangle wave.
Oh Klaas that's a big change to the waveform i will give that a go ,I did think the sync sounded like the problem but didn't think it was a change of waveform more thinking more its was a weak sync pulse .
That's a good experiment i will do tomorrow and have a look at the results on the scope it was something i planned to do for the cd mechanical recorder a while back but other problems took my time up and never got around to it ...
As our ears are not sensitive to wave forms, but sensitive to the volume (strength) of higher and lower sine waves, we do not hear this type of distortion. SSTV is much less sensitive to this, because it is an FM tone. All frequencies are close to each other, 1500 Hz to 2300 Hz, in the audio spectrum. So all tones are recorded at almost the same depth in the tape and at almost the same distance from the gap in the recording head.
Yes not really a problem for tape magnetic recording as you say but harder for record for a record but some thing must still be there as it can be detected by my android phone sstv app least one of its sections .
This distortion is deadly for NBTV video signals. That is the reason that all video tape recorders work with a FM subcarrier, just like SSTV.
Oh i see ...i found the one time i tried it interesting as i was expecting it to work ..i was surprised it didn't...i looked into it just to see if i would get the same result as from the mechanical CD recorder not expecting the same ...well now i know ...good to know !
But do not stop your experiments.! Go on with it, because only if you see it yourself, you are convinced and you learnt from it for life time.
I will go on with it the recording work it is something new to me and interesting to solve the problems ...the slight sstv i managed to record and play back does give me hope things can only get better ,your advice is a big help in working in the right direction Thanks Klaas.