Have Internet Cable and TV Cable with Comcast. Can I run an RG6 cable from
the Wall to my PC TV Video Card, and then from my PC TV Video Card to the
Cable Modem? Or would it be better to run the Wall to a T connector and
then to both the Modem and PC?

Any problems with sharing the same cable connection for both Internet and
TV?

On Wed, 21 Jan 2004 14:56:44 GMT, "Al Franz"
<*deleted*@nospam.netmation.com> wrote:

Al,

You're internet connection is better off with as few splits as
possible before the cable modem. Either make a 3 way split (TV, cable
modem, PC TV card), or make a pair of 2 way splits (internet / TV,
then split TV to TV / PC video card). Either way you need to run 2
separate RG6 cables to your PC (1 to the cable modem, 1 to the video
card).

If you split TV / PC, then at the PC, you split cable modem / video
card, the cable modem will get 25% of the total signal level. If you
make a 3 way split, the cable modem gets 33% total signal level. If
you split TV / cable modem (then split TV to TV / PC video), the cable
modem gets 50% of the total signal level.

As far as I know, connecting the TV video card and cable modem in
series is the same as a split, and will give you 50% the available
signal level there, or 25% total level.

And try to keep the total cable run to the modem as short as possible
too.

Cheers,

Chuck
cacrollthespam@yahoo.com
Spam sucks - PLEASE get rid of the spam before emailing me!
Trusted Computing? Right! http://www.againsttcpa.com/

Chuck wrote:
<Snip>
Inputs can never be connected is parallel (daisy-chained), which I think is
what you are referring to (not series), i.e. a T-connector rather than a
splitter.

Connecting multiple inputs in parallel causes standing waves on the now
characteristic-impedance mis-matched coaxial feedline. This causes large
variations in levels throughout the broadband spectrum, and introduces
phase shift reflections which not only distort the picture, but make it all
but impossible for a cable modem to recover a good RF signal. Additionally,
interactions between impedances on paralleled ports can cause a frequency
suckout which may or may not vary as tuning is changed.

Don't do it.

Splitters are not merely cube-tap parallel connections. They are devices
which divide the power flowing into them in certain pre-defined ways. For a
two port (plus input) device the loss is -3.5 dB per port, or just over
50%. With a three port device (plus input) you have a choice of three -5dB
ports or one -3.5 dB port and two 7 dB ports. A four port (plus input)
device has four -7 dB outputs, leaving you with 25% of the input power at
any one output port.

This power division occurs whether other devices on the splitter are turned
on or off.

Splitter power division also affects the reverse path in the case of a cable
modem, so you can see why you don't want to be attenuating your modem's
transmitted signal back to the head-end any more than you have to.

The isolation output-port to output-port on a good quality splitter is over
-30 dB, that's better than 1000:1 and because of this isolation, each
(splitter) output is matched to the characteristic impedance of the coaxial
cable (75 Ohms) and no output port on a splitter is affected by other
output connections.

Additionally, look for EMI ratings of 130 dB or better. This is a measure of
how well the splitter is shielded, and how well it will keep the cable
signal in, and interference out. This is especially important with a
two-way signal like digital TV or a two-way cable modem. Cheap splitters
are terrible in this regard, and don't have smooth frequency responses
either.

There is enough said on the Internet already as to making proper F fitting
crimps with quality materials and tools by me and others, so I won't
elaborate on that further.

You get the idea.

As was said before, place a two-way splitter at the CATV demarcation point
of your home, run one line to the cable modem, split the other splitter
port as required to feed your TV's and TV card, running a separate
connection from there to each TV or TV card. You can choose splitter losses
and a splitting scheme to deliver stronger signals to your better equipment
and weaker signals to your smaller sets.

Keep in mind that every VCR has a two-port splitter built-in (that's how you
can record one program and watch another), so you'll have an additional
-3.5 dB loss wherever a VCR is in line with a TV.

Rick Kunath

Is there any disadvantage to getting a 3-way splitter instead of a 2-way.
Even if we only use 2 of the outputs do you loose any dB by having a 3rd
output connector on the splitter itself.

Al Franz wrote:

Splitters divide power, so on a two way splitter, each port receives 1/2 the
power (actually slighly less), on a 3 port, 1/3 etc. Also, unused ports
are supposed to be terminated in a resistor, to maintain system impedance.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

Al Franz wrote:

Yes,

As was mentioned unused ports need to be terminated (you can use either a
device or a special terminating cap) both to prevent ingress (noise and
interference getting into the cable) and to maintain ideal performance of
the splitter.

All ports of the splitter will see the designed loss in dB, whether you have
a device connected to them or not. In other words if you get a 3-way
splitter (let's use a -5 dB symmetrical split model for example), and
connect a TV to port 1, a cable modem to port 2, and nothing to port 3,
each of your devices will be at the level -5 dB stamped on the splitter.
The same would be true if you only connected one device to the splitter and
had two unused ports.

Bottom line... never get a splitter with more ports than you actually need.
It lowers the signal to connected devices unnecessarily, and as I mentioned
earlier lowers the upstream signal from a cable modem as it tries to
communicate back the the cable companie's head-end.

Use one and only one two-way split before a cable modem. Port one goes to
the cable modem direct, port two gets split again as you see fit to feed
your televisions and TV cards.

Do it any other way and you may have reliability issues. Know what your
upstream and downstream signal levels are if you deviate from this, and
monitor your connection reliability. If you aren't solid, do as I suggested
above.

Most inside the home cable television troubles are because of improper
splitting arrangements, poor quality splitters, poor quality coaxial cable,
and improperly installed F connectors.

If you have other questions... fire away.

Rick Kunath