RCA 1861, NTSC and a DEC VR-201

From: Allison J Parent <allisonp_at_world.std.com>
Date: Thu Sep 30 17:56:21 1999

<You could try an emitter follower (but you'd have to arrange suitable
<supply rails, since you've got a video signal that goes above and below
<ground. Or an Elantec EL2001 (ditto about the supply rails). Are you sure
<the video signal really goes -ve wrt ground ? (anyone want to
<confirm/deny this?)

the signals do not go below ground. They are driven from pin 6 on the 1861
<sync> through 3.3k to junction of another resitor 1k from pin 7 <video>
and then are tied to a resistor 200ohm to ground the composite video comes
from the junction of the three. The 1861 is powered by +5v so it's not
below ground referenced.

An emitter follower would work but, there is the little problem of the
.6-.7V offset <Vbe> that has to be taken care of. Pulling that juntion
positive with a resistor in the range of 680-1600 ohms may satisfy that.

Allison
Received on Thu Sep 30 1999 - 17:56:21 BST