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G8MNY > TECH 01.03.26 17:45l 114 Lines 4539 Bytes #9 (0) @ WW
BID : 53300_GB7CIP
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Subj: What is Multiplexing?
Path: JH4XSY<N3HYM<KA3VSP<WB4WPF<N2MH4<DK0WUE<VK5LEX<VE3KPG<GB7CIP
Sent: 260301/0841Z @:GB7CIP.#32.GBR.EURO #:53300 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Dec 08)
(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
where each circuit ｳ:::::::ｳ
is on different \:::::/Cable
conductors. '---'
X Band X Band X Band Another example would
Sat A Sat B Sat C be Satellites, where
\' . |'�. /� bands of frequencies
\ |� /�.'. or channels are reused
\ | /' .'�:. on satellites on
Different 'Same different beam headings.
Dish Angle Routes e.g. each 1.5� for comms Sats.
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.
ｳch1 ch2 ch3 ch4 ch5 ch6 ch7 ch8 ch7500
ﾀﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁ/ /ﾄﾁﾄﾄﾄ
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
Left ﾄﾄo Switch
\,_______________________ﾚﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ
Rightﾄﾄo /|\ ｳ Add ﾃﾄﾄ>ﾄｴ 53kHz ﾃﾄﾄﾄ> to Tx
ｳ ﾚﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾀﾄﾄﾂﾄﾄﾙ ｳLow Passｳ
76kHz >ﾄﾄﾁﾄﾄﾄｴ�4ﾃﾄﾄﾄｴ 19kHz ﾃﾄﾄﾄﾄﾄﾙ-20dB ｳ Filter ｳ
ﾀﾄﾄﾙ ｳFilter ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ
ﾀﾄﾄﾄﾄﾄﾄﾄﾙ
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 __________
---------ｴ Pulse ｳ _________
---------ｴ Code ｳ DIGITAL ｳColoured ｳ _____________
---------ｴModulationﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ Light ｳFREQUENCY ｳMulti Strand ｳHIGH
---------ｴ & Time ｳ >ｴFrequencyﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ Fibre Optic ｳCAPACITY
---------ｴ Division ｳ Other >ｴDivision ｳ Other >ｴCable. Space ｳTRUNK
---------ｴMultiplex ｳ Inputs>ｴMultiplexｳ Inputs >ｴDiv MultiplexｳROUTE
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
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 )||(____ ____)||(
___)||(____ｳ_______________________ｳ____)||(______
ｳ ｳ
___ ____ｳ ｳ____ ______
Phantom )||( Balanced )||(
Circuit ___)||(____ Quad ____)||(______
ｳ Cable ｳ
___ ____ｳ_______________________ｳ____ ______
Circuit 2 )||(____ｳ ｳ____)||(
___)||(_________________________________)||(______
How is this 3rd Phantom circuit multiplexed, Space, Frequency or Time?
* 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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