[opendtv] Re: 405 line pictures
- From: flyback1 <flyback1@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 15 Dec 2006 15:13:46 -0500
Allen Le Roy Limberg wrote:
I suppose transmitters may have been purposely adjusted not to
maintain correct black level to avoid murky pictures on cheap receivers.
Al
I visited a B&W TV transmitter site near Orlando in the mid 1960s and
saw first hand how non-linear the modulators
in those old behemoths can be.
To transmit a signal which, when received on a consumer TV, would lock
the sweep circuits properly and have approximately
714 mV of video and 286 mV of sync, it was necesary to 'pre-distort' the
composite signal feeding the exciter
to levels of 550 mV of sync and 450 mV of video.
The engineer on duty showed me the waveform monitors displaying the
signal going in
and then coming back from the transmitter diode demod port.
It's amazing the pictures looked as good as they did.
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