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From: SNIPrf_man_frTHIS@yahoo.com (Frank Raffaeli)
Subject: Re: DVD to TV: Need a Schematic Drawing of a DVD RF Modulator. (a.k.a. S-Video & Audio to Coax Converter)
Date: 12 Dec 2002 16:37:35 -0800
NNTP-Posting-Date: 13 Dec 2002 00:37:35 GMT
Ty <email@example.com> wrote in message news:...
> Device Description:
> This device converts the signal coming from the RCA outs on the back of a
> DVD player to the Coaxial input on the back of a TV. More specifically:
> DVD outs; One Left Audio RCA out, One Right Audio RCA out, and One Video
> RCA out. The TV for this experiment of course only has one Coaxial input.
> The objective if your kind and generous enough to accept it:
> To provide a schematic drawing of the device described above.
I have seen some pretty good application schematics in this thread.
This project will require tenacity. I would recommend understanding
the principles first, rather than just trying to hunt down a
schematic. I'm going to assume your application for for a North
American TV system. Here is one plan of action, in increasing order of
complexity. I've elaborated on 1-3:
1) Build a 'jammer'
2) add video modulation
3) add audio carrier to the composite video
4) add stereo
5) add vestigial sideband filtering
1) Build a signal source for channel 3 or 4 (~65 MHz, I think) ...
Check references. Make it tunable. There are circuits on the web for
home-brew oscillators. You can use an inexpensive transistor like a
2N3904. Use a slug-tuned coil and fixed caps if possible. Tune the
oscillator and you should be able to get a 'blank' screen on your
channel. Make sure you are at the fundamental frequency, e.g. ... the
oscillator is not 1/2 or 1/3 etc ... of the desired frequency.
2) Amplitude modulate the oscillator above with the composite video
... one imprecise but simple method is to invert the composite video
signal (use another transistor, or a high speed op-amp) and use this
signal to change the base bias of the oscillator transistor. There are
better ways ... see 'supressed carrier modulation' etc ... You want
the max signal to occur at the sync tips of the video and the minimum
signal to occur at the peaks (white). The video signal should be D.C.
restored relative to the 'back porch' and DC coupled. Look up
'clamping' circuits as well.
3) Add a 4.5 MHz (if North American) carrier at 10% of the full scale
video to the composite signal. Frequency modulate this 4.5 MHz carrier
with a 25 kHz deviation. I forget what the pre-emphasis is. You might
be able to crudely generate this signal with a carefully tuned 4046.
Best of luck,
Frank W. Raffaeli
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