Dustin said:
I got a wire that splits the red color (right audio) wire into 2 red
wires, would it be possible to use this wire on a yellow wire spot
(video) to make it so that there are 2 yellow wires. Or will something
bad happen to the wire?
There is a difference between audio and video.
Frequency-wise, audio only stretches from 20Hz to 20KHz or so.
Wire at those frequencies doesn't behave like a transmission
line, but more like a lumped load. You can split an audio
signal down multiple paths, subject to the loading of the
device at the end of each wire. (I.e. Put a big speaker
on a headphone circuit and it'll be pretty weak.) In other
words, audio doesn't really care what you do to the wires.
Higher frequency signals want to be maintained in a controlled
environment. That environment is a transmission line.
Driver -----75 ohms ------- coaxial cable --------
75 ohms |
GND --- 75 ohms
| |
GND GND
In the figure above, the driver has an "output impedance"
of 75 ohms. If a signal is reflected somewhere inside the
cable, and the reflected signal comes back at the driver,
the 75 ohm impedance of the driver, looks like an infinitely
long length of cable - the reflection is absorbed by that
perfectly matched impedance. Similarly, in the forward
direction, the abrupt end of the transmission line, at the
end of the cable, terminates in a 75 ohm load in the TV
or VCR.
This second chunk of schematic on this page, shows a video
receiving circuit, with a 75 ohm resistor to ground. That
matches the transmission line impedance of the rest of the
cabling. The 47 microfarad capacitor is for AC coupling of
the video signal. (Another thread I was reading, said the
baseband video goes down to 2 to 5 Hz, and that is why the
capacitor is so large. The video bandwidth is measured in
megahertz, much more than the kilohertz of audio.)
http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.html#ASCIISCHEM_011
Now, consider what you are trying to do:
+-------------- 75 ohm load
|
Driver -----75ohms -------+
|
+-------------- 75 ohm load
At the "fork" in the circuit, the line no longer
looks like 75 ohms. There will be reflections from
the fork, which will distort the signal.
http://www.epanorama.net/links/videocircuits.html#distribution
This shows a very simple video distribution circuit. It
presents a 75 ohm load to the source. The emitter follower
circuit is used to make "copies" of the signal. The
circuit is designed to have a roughly 75 ohm output
impedance.
http://www.anatekcorp.com/driving.htm
Good video gear will have a video in and a video out.
Depending on the mode of the device, the video out may
in fact be a copy of the video in, and that saves you on
needing to find a video buffering solution.
This thread basically discusses the issue. If you are
sending RF TV signals (like from a TV antenna), the
signal can withstand attenuation. A TV RF input has
AGC (automatic gain control), and if a splitter is used
to make two copies of a signal, the RF amplifier simply
turns up the gain. A baseband video circuit will not
likely be as well endowed, and expects to find a signal
of the proper amplitude (about 1V into 75 ohms). If a
splitter is used on a baseband video signal, the size
of the signal is reduced by the splitter.
http://www.epanorama.net/phpBB2/viewtopic.php?t=1755
This Radio Shack product makes four copies of A/V signals,
and accepts either a composite video or a S-video input
signal. The output is composite video or S-video on each
output channel. The device uses an AC adapter, to get
power for the amplifier circuit inside. ($44)
This would be the right way to solve the problem.
http://www.radioshack.com/product/index.jsp?parentPage=search&cp=&productId=2103065
http://RSK.imageg.net/graphics/uc/rsk/Support/ProductManuals/1501172_PM_EN.pdf
You can try "forking" the signal as you propose to, but
don't be surprised if the result is crap.
HTH,
Paul
