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 What is
Balanced & Unbalanced?Signals
A difference in voltage between two conductors is how a receiver sees a signal,
a potential difference. As a result, it takes two wires to make a lane for a
signal to travel on. In fiber optic, light only needs the one glass tube to
make its journey. As electric signals travel through conductors, the electrons
that make the signal generate magnetic fields around their conductors. This
”radiation” of magnetic fields affects electrons in nearby conductors causing a
false signal in those nearby conductors. This problem is referred to as
”crosstalk”. Ways to conquer crosstalk are shown below. In fiber optic, there
is NO crosstalk, light traveling through the glass tube doesn’t get out of the
cable and can’t effect adjacent cables because photons don’t generate magnetic
fields like electrons do. Unbalanced RS232, Centronics
parallel, IEEE 1284, USB, Thinnet, Audio, Video, and “single end” SCSI are just
a few examples of Unbalanced signals. Most unbalanced signals travel Coax
cables but a few do not. As mentioned before, it takes two wires to make a lane
for data. In the case of the coax, one wire runs the middle while the other
wire is the foil or braid that wraps around the outside. The two signals of an
unbalanced connection are referred to as “signal” and “ground”. The ground is
the zero reference while the signal has a voltage level that is above or below
zero. This voltage level determines weather the signal is a 1 or a 0 (VGA,
Audio & Video are Analog signals, the analog signal can have a voltage level
anywhere between the high and low voltage levels). In RS232, the “ground” for
all signals is shared on one conductor; this is also true of some other
Unbalanced signals. RS232, Parallel and SCSI are more vulnerable to crosstalk
since they have more than one signal in the same jacket and in some cases,
sharing the same ground. Parallel and Single End SCSI suffer the worst, We
usually don’t guarantee a parallel cable (Centronic or IEEE 1284) to work any
longer than 40 to 50 feet. Because the signal is stronger for RS232, it can
usually reach lengths of 300 feet, but as the data or BAUD rate is increased,
the range is shortened. In coax cables, the “radiation” generated by the signal
on the center wire gets absorbed by the foil or braid on the outside. Coax
cables are the way to fight against crosstalk for Unbalanced signals. Balanced RS422, Differential SCSI,
Ethernet 10Base-T, and Ethernet 100Base-T are just a few examples of balanced
signals. Balanced signals have often been called “current loop” signals and
travel on “twisted pairs” (UTP for Unshielded Twisted Pair or STP for Shielded
Twisted Pair). The two signals in a balanced pair are like opposite charges of
each other. What that means is if one wire has 12 volts, the other wire will
have -12 volts. As the signal travels the pair, one wire radiates a magnetic
field but its partner wire generates an opposite field, the two fields cancel
out. This canceling is how balanced signals conquer crosstalk. Since Twisted
pair wire is usually cheaper then Coax wire, balanced signals are more popular.
Ethernet used to travel on a Coax (10Base-2 or Thinnet) but lately has been
traveling on twisted pairs (10Base-T, 100Base-T). 100Base-T is so fast that
the wire has to meet some specifications to carry it. The Cat 5 cable requires
that the pairs be twisted tight enough to continue the canceling of the
radiation. Also if the pairs are untwisted too much, the canceling won’t happen
and you’ll get that dreaded crosstalk. Impedance The
impedance is a value determined by the capacitance and attenuation effects that
a wire has on the signal traveling through it. It isn’t necessary to explain
the full details. Each signal has it’s own rating (Arcnet has 93 ohm, Audio and
Video have 75 ohm, and Thinnet has 50 ohm). Using a cable with the wrong rating
will distort the signal. Twisted pair cables also have an “impedance” but most
of the time, their name usually determines the signal they carry (a Cat 5 is
made for 100Base-T). What is the Balun? Some users
have Unbalanced signals like Arcnet or Thinnet,
which use coax cables, but they do not want to pull expensive coax cables. The
Balun allows them to string twisted pair in place of coax. Baluns are used in
pairs, one at each end of the twisted pair wire. The coax side of the Balun
has an impedance rating and you would need to find the balun with the impedance
rating to match the signal. The word “Balun” comes from combining the words
”BALanced” with “UNbalanced”. PLEASE NOTE: Putting a Balun on a Thinnet port
doesn’t convert it to 10Base-T, a converter would be needed for that.
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