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| Composite video issue |
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| maginnovision:
I'm not sure what you're looking for but here is a SS triggering on lines instead of frames. |
| vk6zgo:
--- Quote from: maginnovision on January 13, 2019, 03:57:36 am ---I'm not sure what you're looking for but here is a SS triggering on lines instead of frames. --- End quote --- I think you may be right about the RF getting into your video. Analog video signals should look like the ones in these links. http://www.radioradar.net/en/measurements_technics/oscilloscope_display.html https://electronics.stackexchange.com/questions/66588/how-do-analog-video-signals-work |
| maginnovision:
--- Quote from: vk6zgo on January 13, 2019, 04:32:29 am --- --- Quote from: maginnovision on January 13, 2019, 03:57:36 am ---I'm not sure what you're looking for but here is a SS triggering on lines instead of frames. --- End quote --- I think you may be right about the RF getting into your video. Analog video signals should look like the ones in these links. http://www.radioradar.net/en/measurements_technics/oscilloscope_display.html https://electronics.stackexchange.com/questions/66588/how-do-analog-video-signals-work --- End quote --- I'm not sure, it's pretty far outside my wheelhouse. The modulator is based on LM1889 and this unit doesn't properly ground the box(ground spring is missing). Here is one more triggering on lines without the RF modulator. The problem is without the modulator I don't get color information so it isn't really something I'm worried about. The other test unit looks much better but I prefer to test with the worst case. |
| vk6zgo:
--- Quote from: maginnovision on January 13, 2019, 04:40:31 am --- I'm not sure, it's pretty far outside my wheelhouse. The modulator is based on LM1889 and this unit doesn't properly ground the box(ground spring is missing). Here is one more triggering on lines without the RF modulator. The problem is without the modulator I don't get color information --- End quote --- This is the second comment you made which rings alarm bells. The first was in the OP,where you said --- Quote ---The input to the circuit is the output of an RF modulator. The output is to the TV. --- End quote --- The output of the RF modulator should be a modulated RF envelope as shown in this link:- https://www.britannica.com/technology/television-technology/Principles-of-television-systems There should not be a recognisable baseband video signal at the RF output of the LM1889, unless it is faulty, wrongly wired, or perhaps, unpowered. Look at this link now:- http://rbsfm.org/Downloads/Datasheet/LM/LM1889.PDF The LM1889 is intended, as far as I can determine, to combine a Luma signal (on pin 12) with two separate Colour Difference signals (R-Y on pin 2) & (B-Y on pin 4), to produce a Composite NTSC colour video signal, prior to modulation. Also,as far as I can see, this signal, once produced, does not appear as an output on any of the pins of the IC, but passes directly to the RF modulation section where it amplitude modulates a VHF RF carrier, giving a signal which can be received by a standard analog TV receiver via its antenna input. Your last waveform was, I assume, on Pin 12.( for some unfathomable reason, the manufacturers just label that pin "video") It is a horrible Luma signal, which raises the spectre of your source of these video drive signals being faulty. |
| maginnovision:
--- Quote from: vk6zgo on January 14, 2019, 03:04:41 am --- --- Quote from: maginnovision on January 13, 2019, 04:40:31 am --- I'm not sure, it's pretty far outside my wheelhouse. The modulator is based on LM1889 and this unit doesn't properly ground the box(ground spring is missing). Here is one more triggering on lines without the RF modulator. The problem is without the modulator I don't get color information --- End quote --- This is the second comment you made which rings alarm bells. The first was in the OP,where you said --- Quote ---The input to the circuit is the output of an RF modulator. The output is to the TV. --- End quote --- The output of the RF modulator should be a modulated RF envelope as shown in this link:- https://www.britannica.com/technology/television-technology/Principles-of-television-systems There should not be a recognisable baseband video signal at the RF output of the LM1889, unless it is faulty, wrongly wired, or perhaps, unpowered. Look at this link now:- http://rbsfm.org/Downloads/Datasheet/LM/LM1889.PDF The LM1889 is intended, as far as I can determine, to combine a Luma signal (on pin 12) with two separate Colour Difference signals (R-Y on pin 2) & (B-Y on pin 4), to produce a Composite NTSC colour video signal, prior to modulation. Also,as far as I can see, this signal, once produced, does not appear as an output on any of the pins of the IC, but passes directly to the RF modulation section where it amplitude modulates a VHF RF carrier, giving a signal which can be received by a standard analog TV receiver via its antenna input. Your last waveform was, I assume, on Pin 12.( for some unfathomable reason, the manufacturers just label that pin "video") It is a horrible Luma signal, which raises the spectre of your source of these video drive signals being faulty. --- End quote --- Actually no, it is from pin 13 of the LM1889, all the wavefoms are from pin 13 or the output of the circuit I posted. When I say it's the output of the modulator it's simply because the signal is modified by the modulator and it's another thing entirely when it's not connected. I can't modify the modulator, I can't modify the board or chips that feed it either those products are already done and not mine. I'll attach a picture of the modulator. I'm not going to pretend the waveforms look good or great though, they don't and if it were my project I would make sure it looked good. However they do produce acceptable video aside from seeing the 60hz 5 times on the screen. This board again has about 100mV 60hz AC riding along the power rails and the modulator gets 10V, 2.5V and -5V. I haven't even bothered checking the vertical and horizontal drive signals but the chroma clock looks fine. Honestly if I had more time and was more knowledgeable on the subject I would probably replace the modulator with a different circuit altogether to get cleaner video from the get go. The way I have to do it now relies on the modulator or just gives B & W. I don't have the time or knowledge though. |
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