Message 26476 in TECH.WW
From: G8MNY
Date: Thu, 23 Jul 26 08:51:00 Z
Newsgroups: TECH.WW
Subject: What is Multiplexing?
Message-ID: <68_GB7CIP>
Path: N2MH4|GB7BED|EI2GYB|GB7CIP
R:260723/0852Z 34232@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260723/0852Z 14735@GB7BED.#21.GBR.EU LinBPQ6.0.25
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 26)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
What is Multiplexing
This is where several circuits or channels use the same route/system.
There are only 3 types of Multiplexing or MUX.
1/ Space Division
2/ Frequency Division
3/ Time Division
1/ Space Division Multiplexing
This is not obvious, but is the simplest, it is where the circuits occupy
different physical space.
Examples are multi .---.
conductor cable /:::::\ : = Circuit pairs
is on different \:::::/Cable
conductors. '---'
X Band X Band X Band Another example would
Sat A Sat B Sat C be Satellites, where
Different 'Same different beam headings.
2/ Frequency Division Multiplexing
This is where the channels are split up on different frequencies like on a
radio. e.g. they all share the same aerial. Cable TV & old cable SSB telephone
system cram 1000s of channels down a coax this way.
4k 8k 12k 16k 20k 24k 28k 32k .... 30MHz
Some high capacity Fibre optics systems still use it with different coloured
light to multiply the fibre capacity 1000s of times.
3/ Time Division Multiplexing *
This is where channel is swapped for another normally in sequence. Simplest
example would be day & nighttime TV by 2 different stations. Further example is
Stereo Radio, where the left & right channels are swapped over at 76000 times a
second. Note a synchronisation system is needed to maintain channel separation.
76kHz
A switched audio system like this used to be used for busy transatlantic phone
calls, only switching in the those people who where actually talking.
More complex example is DAB/Digital TV where quality/digital statistical
multiplexing determines which channel get sent in the data stream next.
All 3 at once!
It is possible to get confused if more than one multiplex method is used.
Channels __________
Then huge capacities are possible with all 3 in use.
CONCLUSION
Quite often several of the above are used at once all invisibly computer
controlled. The advantage is more efficiency use of a route, but as a cost of
far more complexity and reduced reliability. E.g. a DAB Radio is running the
equivalent of a pentium processor to decode the bit stream.
QUESTION.
Now just ponder this:- Take two balanced 600ohm lines (diagonals of a quad
cable) and using balanced transformers (or op amps) make a 3rd circuit using
the centre tap phantoms...
___ _________________________________ ______
Circuit 1 )||(____ ____)||(
Phantom )||( Balanced )||(
Circuit ___)||(____ Quad ____)||(______
___)||(_________________________________)||(______
How is this 3rd Phantom circuit multiplexed, Space, Frequency or Time?
Actully it is a rare voltage multplexing! Where signals are added &
subtracted to produce the seperate chanels.
* See my TECH bul on "FM Stereo Radio Principles"
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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