On Mon, 12 Apr 2004 23:31:06 +0000, Rico Rivera wrote:

snip

- What I don't understand is then Q2 is on how is the video line is 0.25
Volts.

- Also, why when Q1 and Q2 is off the video line is at 1 volt.

- And my last question is R5 used for impedance matching?

I tried to work out several combinations and I didn't get the indicated
voltage levels described above. Thanks in advance for any help.



R5 is part of the series chain 220R+75R+external 75R which gives you about
1v when both transistors are off. Note that the external 75R isn't shown
on the drawing, but it forms a voltage divider with the internal 75R!

with Q2 on, you have 33R in parallel with (75R+75R), giving about 27R. The
output voltage, taken across the lower 75R (external) is then half of
0.546v, which is pretty close to 0.25v.

--
Cheers...
Mick
Gave up on viruses & trojans - moved to Linux... :-)
Nascom & Gemini info at http://www.nascom.info