Attenuation of output signal

[RoyEstes]

Greetings everyone.

I'm trying to figure out the exact characteristics of the analog NBTV signal being output by the camera through a cable.

The standard covers very much everything, except for the attenuation of the signal, which I'd have presumed to be at least -3dB for practical reasons, but I don't read that in the spec (not talking about either analog or digital storage, just the signal itself going out of the camera and into the televisor).

What am I missing here?

Much appreciated.

[Steve Anderson]

Generally there isn't any attenuation of the baseband NBTV signal. As the bandwidth is so low, much the same as an audio signal, the impedance of any cable/connectors etc. is generally ignored. Sources are low-Z and inputs are high-Z. There is a nominal signal level of 1V peak-to-peak.

But it's up to each user/constructor to define his/her own in-house standards. I generally stick to 75 ohn in and out at 1V p-p including composite syncs, but there's no real reason to do so, and most don't. If two members want to construct NBTV equipment which will interface with each other it would be prudent to agree a standard at the start. This also applies to other signal parametrs, like voltages, frequencies, timing, line quantity, generally all normal signal standards that require definition.

I think that generally sums up the situation, but if I've missed anything, just ask....

There is a broadly defined 32-line 12.5Hz NBTVA 'standard', but not everyone sticks to it, I have used different line quantities many times, e.g 32, 48, 72-lines at various frame-rates with various frame and line-sync arrangements.

The bandwidth of 72-lines at even 12.5Hz is getting slightly outside what could be called 'audio', but not quite what I would consider 'video'....even though it IS a video signal!

Steve A.

[Klaas Robers]

The definition of NBTVA video signals can be found on the NBTVA website:

1. go to "www.nbtv.org"
2. select: Handbook in the line just below the header
3. select: CLICK HERE to enter between the NBTV picures
4. select: [ Contents ] in the line below the header
5. select chapter 25. NBTV standards and recommendations

and you will find the different definitions as they are written in the NBTVA handbook.

We use normal stereo audio cords to distribute the signals, right = sound, left = NBTV video. And there is no attenuation with a low ohmic output (500 ohms or less) and a high ohmic input (5000 ohms or more).

Next to that, in most cases a monitor has in most cases a video level control, called "Contrast", so the precise amplitude of the signal is not that important.

[Steve Anderson]

Thanks Klaas, that definition I had forgotten about, that should help Roy (the OP) out...

Steve A.

[RoyEstes]

Thank you both for the explanations , that's basically all I needed to know, meaning confirmation that the standard (which I called "the spec") appeared to specify no further attenuation.

In any event, the rationale behind the question stems from the need to check the signal against whatever standards-complying hardware would produce under ideal conditions, thus say I lay a scope on the wires, I should be seeing fundamentally the same as described plus-minus minimal deviation expected from somewhat different choice components.