Coaxial vs CAT 5

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Ro Cathain
Guest

Posted: Tue Feb 08, 2005 7:47 pm Post subject: Coaxial vs CAT 5

I have Cat 5 and Coaxial cabling installed in my house. I want to feed (a) an audio signal, (b) video signal, from a wirelessly controlled sub-floor PC to wall connections. So, I anticipate using 4 of the Cat 5 wires to feed an audio signal to hifi equipment. (ok quality?) Then, should I use the other cables of the CAT 5 to make up a scart connection to the TV... or should I use the co-axial cable for best quality??? Cheers.

Dmitri(Cabling-Design.com
Guest

Posted: Tue Feb 08, 2005 8:16 pm Post subject: Re: Coaxial vs CAT 5

Ro Cathain wrote:

Quote:

I have Cat 5 and Coaxial cabling installed in my house.

I want to feed (a) an audio signal, (b) video signal, from a wirelessly
controlled sub-floor PC to wall connections.

So, I anticipate using 4 of the Cat 5 wires to feed an audio signal to
hifi
equipment. (ok quality?)

Then, should I use the other cables of the CAT 5 to make up a scart
connection to the TV... or should I use the co-axial cable for best
quality???

Cheers.

It is best to use CAT5 for both audio and video because the coax cable is
designed for broadband video (TV). One thing you should look for in terms
of quality of the signal is a balun (balanced-to-unbalanced transformer)
on both ends. I have never seen one for SCART though. If your equipment
has either S-Video or RCA outputs, use those instead. For short distances
you could even go with unbalanced outputs. That is, use simple direct -
connection jacks. Besides, check with your equipment manuals - some of the
outputs may already be balanced, so you can save some money by not buying
one of the two baluns that are required to complete one circuit. one
circuit represents one channel of audio or one baseband video signal.

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------

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Ro Cathain
Guest

Posted: Tue Feb 08, 2005 9:44 pm Post subject: Re: Coaxial vs CAT 5

Thanks for that :-)

"Dmitri(Cabling-Design.com)" <info_at_cabling-design_dot_com@foo.com> wrote
in message news:bJ4Od.1478589$f47.252805@news.easynews.com...

Quote:

Ro Cathain wrote:

I have Cat 5 and Coaxial cabling installed in my house.

I want to feed (a) an audio signal, (b) video signal, from a wirelessly
controlled sub-floor PC to wall connections.

So, I anticipate using 4 of the Cat 5 wires to feed an audio signal to
hifi
equipment. (ok quality?)

Then, should I use the other cables of the CAT 5 to make up a scart
connection to the TV... or should I use the co-axial cable for best
quality???

Cheers.

It is best to use CAT5 for both audio and video because the coax cable is
designed for broadband video (TV). One thing you should look for in terms
of quality of the signal is a balun (balanced-to-unbalanced transformer)
on both ends. I have never seen one for SCART though. If your equipment
has either S-Video or RCA outputs, use those instead. For short distances
you could even go with unbalanced outputs. That is, use simple direct -
connection jacks. Besides, check with your equipment manuals - some of the
outputs may already be balanced, so you can save some money by not buying
one of the two baluns that are required to complete one circuit. one
circuit represents one channel of audio or one baseband video signal.

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------

##-----------------------------------------------##
Article posted with Cabling-Design.com Newsgroup Archive
http://www.cabling-design.com/forums
no-spam read and post WWW interface to your favorite newsgroup -
comp.dcom.cabling - 1210 messages and counting!
##-----------------------------------------------##

Tomi Holger Engdahl
Guest

Posted: Wed Feb 09, 2005 9:23 pm Post subject: Re: Coaxial vs CAT 5

info_at_cabling-design_dot_com@foo.com (Dmitri(Cabling-Design.com)) writes:

Quote:

All TV video signals are originally designed to be transfered through
75 ohm coax cable. That's the what the video professionals,
TV broadcasters, majority of CCTV installations etc. use.
There are various kinds of 75 ohm coaxial cables available (like
there are varioust types of 50 ohm ciaxila cables as well),
thicker, thinner, higher loss, lower loss, optimized for
high frequency use, designed for lower frequency use in mind,
cables that do well all frequencies well from DC to highest frequencies.
Propably most common type of cable used to carry video signals is
RG-59 B/U type 75 ohm coaxial cable. Many other 75 ohm cioaxial cables
work very all also. Generally if you take practically any 75 ohm coaxial
cable, evenones designed for antenna installations only in mind,
those carry baseband video signal at least somehow acceptably..
There are some data of some vieo coaxial cables at
http://www.epanorama.net/documents/video/videocoax.html

Nowadays it has also been possible to tranfer vidoe over
other kind of wire types, for example though CAT5 twisted pair
wiring with pretty good quality and quite cheaply.
Because the video is originally designed for 75 ohm coaxial
cable, you need to use a balun adapter between your video equipment
and the twisted pair wiring. This balun adapter adapts the unbalanced
video signal to balaced signal that can travel through twísted
pair wiring well and maybe also adapt the 75 ohm impedance to 100 ohm
wiring (there are many adapters that do not adapt the impedance,
they just rely that the 75 ohm - 100 ohm mismatch does not
cause too severe problems to picture quality at normal uses,
and usually this is true).

Quote:

One thing you should look for in terms
of quality of the signal is a balun (balanced-to-unbalanced transformer)
on both ends.

You need to use baluns for both audio and video signal if we are
talking about the audio and video signals that ae used in consumer
audio equipment, because both of those signal interfaces normally unbalanced
on those equipment.

Video and audio signals need different kind of balun transformer designs
to work well. There are commercial adapters available that have
baluns for both audio and vidoe signals built inside on compact unit.
It is also possible to build such adapters yourself. I have done that.
For audio signals the balun is notnign else than just 1:1 audio
isolation transformer. For video signals either a current mode balun
(common mode coil) or 75ohm-100ohm video isolation + impedance adaptation
transformer (possibly with DC blocking capacitor in input) is used.
Components are available for those tasks.

Quote:

I have never seen one for SCART though. If your equipment
has either S-Video or RCA outputs, use those instead.

I have never seen blauns with SCART interface either.
Generally with SCART interface you need to take an adapter that
for example adapts the SCART connector signals to one video connector
(S-video connector or composite video RCA) and stereo audio signals
(RCA connectors). Then you just wire those to your adapter
that adapts those signals to CAT5 wiring.

Quote:

For short distances you could even go with unbalanced outputs.
That is, use simple direct - connection jacks.

Very short distances whee cables are away from noise sources
direct connection to jacks might work somehow..
With shielded CAT5 wiring usually somewhat better than with more
common unshielded CAT5 wiring. In most practical
real world systems this kind of direct connection leads to a system
that picks lots of humming noise.. The unshielded CAT5 cabling resistance
against outside noise lies with the combination of use of twisted pair
wires and use of balanced signal sources+receivers. The twists and
balanced signal source make the systme so that the noise picked
by the wires is picked in such way that it gets canceled in the
balanced receiver. If you connect this wires to unbalanced signal source
and unbalanced signal receiver, those properties do not work, and the
noise that gets picked up the wiring gets added to the noise
(the twisted pair signal carrying wire picks less noise compared
to untwisted wire, but considerably more noise than a properly
shielded signal wire would pick in the same environment).

Quote:

Besides, check with your equipment manuals - some of the
outputs may already be balanced, so you can save some money by not buying
one of the two baluns that are required to complete one circuit. one
circuit represents one channel of audio or one baseband video signal.

That's one option if you have equipment that use this kind of interface.
balanced audio signals are seen on many professional audio equipment
and some expensive home hifi equipment.
I have seen balanced video signal interfaces built in only on some
CCTV cameras and related CCTV equipment... Practically other video
equipment I have seen have used "normal" unbalanced video interface
(connectors being usually RCA, BNC, SCART or S-video minidin).

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

James Knott
Guest

Posted: Wed Feb 09, 2005 9:43 pm Post subject: Re: Coaxial vs CAT 5

Tomi Holger Engdahl wrote:

Quote:

Nowadays it has also been possible to tranfer vidoe over
other kind of wire types, for example though CAT5 twisted pair
wiring with pretty good quality and quite cheaply.
Because the video is originally designed for 75 ohm coaxial
cable, you need to use a balun adapter between your video equipment
and the twisted pair wiring. This balun adapter adapts the unbalanced
video signal to balaced signal that can travel through twísted
pair wiring well and maybe also adapt the 75 ohm impedance to 100 ohm
wiring (there are many adapters that do not adapt the impedance,
they just rely that the 75 ohm - 100 ohm mismatch does not
cause too severe problems to picture quality at normal uses,
and usually this is true).

One thing that will cause problems, is the DC component of a composite video
signal. Transformers don't pass DC.

Al Dykes
Guest

Posted: Wed Feb 09, 2005 11:04 pm Post subject: Re: Coaxial vs CAT 5

In article <bJ4Od.1478589$f47.252805@news.easynews.com>,
Dmitri(Cabling-Design.com) <info_at_cabling-design_dot_com@foo.com> wrote:

Quote:

isn't anyone concerned with high-end rolloff for audio on UTP due to
the capacitance ?

For speakers UTP ad too much resistance.

--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Dmitri(Cabling-Design.com
Guest

Posted: Thu Feb 10, 2005 12:04 am Post subject: Re: Coaxial vs CAT 5

Al Dykes wrote:

Quote:

isn't anyone concerned with high-end rolloff for audio on UTP due to
the capacitance ?

The standard audio interconnect cables have HIGHER capacity (30 pf/ft)
than CAT5E UTP (15 pf/ft), so this is not a problem at all.

Quote:

For speakers UTP ad too much resistance.

You normally don't drive a speaker via UTP (although possible with
multiple pairs in parallel). You'd normally send a line level signal via
UTP, which works just perfect as long as it's balanced. Even unbalanced on
short distances is OK.

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------

##-----------------------------------------------#
Article posted with Cabling-Design.com Newsgroup Archiv
http://www.cabling-design.com/forum
no-spam read and post WWW interface to your favorite newsgroup -
comp.dcom.cabling - 1222 messages and counting
##-----------------------------------------------##

Robert Redelmeier
Guest

Posted: Thu Feb 10, 2005 12:07 am Post subject: Re: Coaxial vs CAT 5

Al Dykes <adykes@panix.com> wrote:

Quote:

isn't anyone concerned with high-end rolloff for
audio on UTP due to the capacitance ?

LOL! Do you think we have Golden Ears? Odd "capacitance"
that doesn't affect 100 MHz would somehow disturb 10kHz.

Quote:

For speakers UTP ad too much resistance.

This may be true for some low ohm speakers, but the
solution is usually just to boost the volume.

FWIW, I'm using about 50' of 24ga Cat5 to wire the
satellite speakers on a 5.1 audio system. Maybe
a bit softer (~3dB lower volume) than 20ga.

-- Robert

Ed Nielsen
Guest

Posted: Thu Feb 10, 2005 7:29 am Post subject: Re: Coaxial vs CAT 5

Or you could modulate the A/V outputs of your PC onto a TV channel, feed
it from the PC to the distribution center, and send it via the CATV
distribution system to every outlet in the house. That way, at any TV
in the house, you can tune to channel 85 (or whatever channel you
modulate the PC to) and there it is. At your entertainment center, tune
the VCR to channel 85 to listen to your PC through your entertainment
system.

CIAO!

Ed

Ro Cathain wrote:

Quote:

I have Cat 5 and Coaxial cabling installed in my house.

I want to feed (a) an audio signal, (b) video signal, from a wirelessly
controlled sub-floor PC to wall connections.

So, I anticipate using 4 of the Cat 5 wires to feed an audio signal to hifi
equipment. (ok quality?)

Then, should I use the other cables of the CAT 5 to make up a scart
connection to the TV... or should I use the co-axial cable for best
quality???

Cheers.

Tomi Holger Engdahl
Guest

Posted: Thu Feb 10, 2005 2:43 pm Post subject: Re: Coaxial vs CAT 5

James Knott <james.knott@rogers.com> writes:

Quote:

Tomi Holger Engdahl wrote:

Nowadays it has also been possible to tranfer vidoe over
other kind of wire types, for example though CAT5 twisted pair
wiring with pretty good quality and quite cheaply.
Because the video is originally designed for 75 ohm coaxial
cable, you need to use a balun adapter between your video equipment
and the twisted pair wiring. This balun adapter adapts the unbalanced
video signal to balaced signal that can travel through twísted
pair wiring well and maybe also adapt the 75 ohm impedance to 100 ohm
wiring (there are many adapters that do not adapt the impedance,
they just rely that the 75 ohm - 100 ohm mismatch does not
cause too severe problems to picture quality at normal uses,
and usually this is true).

One thing that will cause problems, is the DC component of a composite video
signal. Transformers don't pass DC.

A normal transformer with isolated primary and secondary does not
pass DC. That's true. There are video applications where
the DC matters and there are video applications where
the signal path does not need to pass DC through.
For example very many video transmission paths (fore example
when carryuing composie video signal) are AC coupled originally.
There is usually is usually a capcitor in the video output circuits
and video input circuits. This makes the system AC coupled.
The missing video DC level is restored on the video signa reception
with a black level clamp circuit that sets the DC level of black
picture to right DC level. Many video transmission paths
do not need to pass DC. And for those video isolation transformers
that apass frequencies from 50 Hz to highest video frequency
work well.

For the applications where there is need to pass DC there are
balun designs that can pass DC. Those are current mode baluns
(=common mode coil) that do blun conversion but can't provide
you galvanic isolation (between in and out) and can't easily
provide impdance matching (input impedance = output impedance).

I have used both types of baluns for video applications.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

Tomi Holger Engdahl
Guest

Posted: Thu Feb 10, 2005 2:58 pm Post subject: Re: Coaxial vs CAT 5

Robert Redelmeier <redelm@ev1.net.invalid> writes:

Quote:

Al Dykes <adykes@panix.com> wrote:
isn't anyone concerned with high-end rolloff for
audio on UTP due to the capacitance ?

LOL! Do you think we have Golden Ears? Odd "capacitance"
that doesn't affect 100 MHz would somehow disturb 10kHz.

The capacitance does affect 100 MHz signals on the cable,
and it will affect the 10 kHz audio signal as well.
The capacitance is there. For audio frequency signals
the capacitance is there to affect the high frequency
roll-off, but also the signal source impedance affect
how much this rolloff there is.
For high freuqency applications the CAT5 wiring
is always terminated to 100 ohms signal and source (=low
impedancde) and the cablign works a a transmission line
(it nis no longer modelled as just capacitance, but the
combination iof cable impedance and capacitance form a system
where the effect of just pure capacitance quite much dissapears).

A cable in audio applications for carrying microphone and line level
signals can be modeled as a low-pas filter. A first-order high-cut (or
low-pass) filter is formed by an output's source impedance and the
capacitance of the cable. The frequency at which a filter attenuates 3
dB is called its "corner frequency". With short cables (low
capacitance) and low output impedances, the corner frequency typically
occurs well above the audio band. With longer cables and higher output
impedances,the corner frequency drops and may drop into the audio
band. The formula for the corner frequency is:

F = 1 / (2 * PI * R * C)

where F is the corner frequency in Hz, PI is 3.14, R is the source's
output impedance in Ohms, and C is the cable's total capacitance in
Farads. A first-order filter has a slope of 6 dB per octave. This
means that beyond the corner frequency, the response will drop 6 dB
for each doubling of frequency. Generally it doesn't seem likely that
you would get detectable loss even at 20kHz unless you have one or
more of these conditions: unusually high source impedance (many
kilo-ohms), unusually high capacitance cable or unusually long cable
length (tens of meters).

Typical transmission characteristics of CAT5 wiring:
DC Resistance: 8.99 Ohms/100metres
Capacitance: 13.5-17 pF/feet (45-57 pf/meter)

The capacitance of a normal shielded audio interconnection
cables is typically 2-3 times higher than the capacitance
of the CAT5 wiring!
One meter of typical shielded audio interconnection cable
(RCA cable) has typically capacitance of around 100 picofarads.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

James Knott
Guest

Posted: Thu Feb 10, 2005 6:08 pm Post subject: Re: Coaxial vs CAT 5

Robert Redelmeier wrote:

Quote:

Actually, at least for long distances, cable characteristics are important
at audio frequencies. For example the cable used to run telephone service
to your home, has a significant rolloff within the voice band. The phone
companies use loading coils to flatten the response within the desired
frequency range.

Robert Redelmeier
Guest

Posted: Fri Feb 11, 2005 4:46 am Post subject: Re: Coaxial vs CAT 5

Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:

Quote:

F = 1 / (2 * PI * R * C)

where F is the corner frequency in Hz, PI is 3.14, R is the
source's output impedance in Ohms, and C is the cable's
total capacitance in Farads. A first-order filter has a
slope of 6 dB per octave. This means that beyond the corner
frequency, the response will drop 6 dB for each doubling of
frequency. Generally it doesn't seem likely that you would
get detectable loss even at 20kHz unless you have one or
more of these conditions: unusually high source impedance
(many kilo-ohms), unusually high capacitance cable or
unusually long cable length (tens of meters).

Typical transmission characteristics of CAT5 wiring: DC
Resistance: 8.99 Ohms/100metres Capacitance: 13.5-17 pF/feet
(45-57 pf/meter)

So for a 100m Cat5 cable, at 8 Ohms source impedence, the
corner frequency is 3.9 MHz . I don't hear up that high.
We're talking about speakers on Cat5. A phono cartridge
might have some trouble :)

Quote:

The capacitance of a normal shielded audio interconnection
cables is typically 2-3 times higher than the capacitance
of the CAT5 wiring! One meter of typical shielded audio
interconnection cable (RCA cable) has typically capacitance
of around 100 picofarads.

Good to know. So capacitance is a non-issue for using
Cat5 in audio.

-- Robert

Robert Redelmeier
Guest

Posted: Fri Feb 11, 2005 4:53 am Post subject: Re: Coaxial vs CAT 5

James Knott <james.knott@rogers.com> wrote:

Quote:

Actually, at least for long distances, cable characteristics are
important at audio frequencies. For example the cable used to
run telephone service to your home, has a significant rolloff
within the voice band. The phone companies use loading coils
to flatten the response within the desired frequency range.

Load coils don't go on lines until 20kft (6km). At that distance,
I don't think the Cat0 line would have bandwidth (S/N=1) over 100 kHz.

I thought the load coils were to retain signal strength (volume),
not frequency response.

-- Robert

Tomi Holger Engdahl
Guest

Posted: Fri Feb 11, 2005 8:02 am Post subject: Re: Coaxial vs CAT 5

Robert Redelmeier <redelm@ev1.net.invalid> writes:

Quote:

James Knott <james.knott@rogers.com> wrote:
Actually, at least for long distances, cable characteristics are
important at audio frequencies. For example the cable used to
run telephone service to your home, has a significant rolloff
within the voice band. The phone companies use loading coils
to flatten the response within the desired frequency range.

Load coils don't go on lines until 20kft (6km). At that distance,
I don't think the Cat0 line would have bandwidth (S/N=1) over 100 kHz.

I thought the load coils were to retain signal strength (volume),
not frequency response.

Loading coils have been eariler used to extend the range of a local
loop for voice applications. Load coils are inserted at specific
intervals along the loop (3..6 Kfeet distance). Load coils are
inductors that are added in series with the phone line. They
compensate for the parallel capacitance of the line, which attenuated
the higher voice frequencies more than lower frequencies. By adding
inductance (load coils) periodically into the cable facility, the
capacitive effect can be cancelled, thus causing the attenuation
across the voice band to be equal. Load coils benefit the frequencies
in the high end of the voice spectrum at the expense of the
frequencies above 4 kHz. Load coils are are often found at loops
extending farther than 12,000 ft. A typical load coil is 88mh coil
(type H88), which will cancel 6000 ft of typical telephone cable
capacity. They are typically installed at 6000 feet spacing. Load coils
benefit the normal telephone operation on normal line, but do not
allow modern broadbans services on lines with load coils. Since ADSL
and ISDN depend on frequencies much higher than 4 kHz, they will not
work a coil loaded line, because those highe frequencies cannot pass
through the coils properly. New digital telephone services require
'unloaded' copper pairs. For example all load coils must be removed
for any DSL or ISDN operation.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

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