Post by Michael QuinlanUnfortunately they want to add video/coax outlets, not data. When I
couldn't get there soon enough, they setup a wireless network as a
temporary solution for Internet sharing. When I told them that a wired
solution would not benefit them in terms of Internet connection speed,
they decided to make the wireless permanent.
Is there any possibility of using the existing UTP (currently wired for
telephone only) for video distribution?
The UTP wiring used on modern structured cabling system can be used
to carry variopus video signals. Modern CAT5e and CA6 wiring can
quite easily carry wide variety of signal with suitable adapters.
The UTP can carry nicely baseband video (composite video, S-video,
component video, RGB etc..), audio signals, digital audio,
RF video (antenna/cable TV signals).
The secret to sending signals over UTP is to balance them well in
order to limit both radiation and noise pick up. This kind of
unshielded twisted pair wiring method is used in many CCTV
applications nowadays to use existing in-house twisted pair wiring
instead of installing new coaxial cable for the CCTV camera. For at
least 20 years products have been available capable of transmitting
video using UTP wire.
Video signal can be adapted to UTP wiring using a special balun
transformer between BNC video connector and the wisted pair
wiring. This converter converts the unbalanced audio signal to
balanced signal which nicely travels through the cable. A similar
transformer can be used on the other end of the cable to convert the
video signal back to unbalanced format which fits to BNC
connector. There are both passive solutions (balun transformers) and
active converters available on the market for this application.
CAT5 cable is not great stuff for video signals, but with suitable
adapters it can work well. The converter will convert the unbalanced
video signal to the balanced signal that can nicely go though the
twisted pair cable without picking up too much noise or radiating too
much interference. The converter will also make more or less perfect
impedance matching between 75 ohm video system impedance and around
100 ohm impedance of the wiring.
One of the most demanding applications on the market today is
broadband video, commonly known as CATV or cable television. It
carries a broad range of signals extending from 54 MHz to beyond 600
MHz (usually up to around 900 MHz). Coaxial cable (RG-59 or RG-6) is
commonly used for these applications. There are also some products for
running broadband RF video through CAT5 or better twisted pair wiring.
The solution is to use a small transformer to convert from an
unbalanced to a balanced signal on the sending end and and vice-versa
on the receiving end. Baluns also make the necessary impedance
transformation between coaxial cable (75 ohms) and twisted pair wiring
(100 ohms). The use of CAT 5 for wireband RF video has been pretty
limited because of quite high attenuation, especially at higher
frequencies. The standard specifies attenuation of 24 dB per 100
meters of CAT5 cable, and when frequencies go higher, the attenuation
increases quicly. But the higher quality cables, like CAT5e and CAT6,
reduce the attenuation considerably. In practice with the suitable
amplifiers and suitable adapters you can run the cable TV or
TV antenna RF signal succesfully from tens of meters (or up to
100 meters on good conditions) through modern UTP wiring.
Unshielded twisted pair is suitable cable to carry balanced signals
(balanced audio interfaces in professional equipment), but is far from
optimal for unbalanced signals (like home hifi audio interfaces with
RCA connductors). To properly transfer unbalanced signal over UTP
thesignals need to be balanced (there are baluns for this).
If you need to carry digital audio signals, then the signals from
coaxial S/PDIF interface can be treated in the same way as video
signals (you can use video BNC to UTP adapters for them).
One word to the wise: not all Cat5 converters are alike. Not all of
them are good and there is a quality difference. They don't all use
the same technology to do the signal conversion and you need to
compare which one is good enough for your application.
When transmitting audio and video signals through twisted pair wiring,
use the adapters from the same manufacturer on the both ends of the
cable. There are no generic standards how this kind of adapters work,
so adapters from different manufacturers are most propably not
compatible with each other.
Here are some links on this topic:
http://www.epanorama.net/links/wire_av.html#utpvideo
http://www.nordx.com/public/htmen/pdf/Video_over_Twisted_Pair_Cabling.pdf
http://www.kat5.tv/
http://www.lexel.fi/
http://www.svideo.com/coaxbalun.html
http://www.infinity-cable.com/icp_balun_catv.htm
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/