Transmission Parameters (Facility & Interface Parameters)

8/18/2019 Transmission Parameters (Facility & Interface Parameters)

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TELEPHONECIRCUITS

TRANSMISSION PARAMTERS AND PRIVATE LINE

CIRCUITS John Paul A. C


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INTERFACE PARAMETERS

Station equipment impedances should be 600 Ω resistive othe usable voice band.Station equipment should be isolated from ground by aminimum of 20MΩ dc and 50 kΩ ache basic voice!grade telephone circuit is a "002 channel

he circuit gain at "k#$ is " d% belo& the speci'ed in!bandsignal po&er.he gain at ( k#$ must be at least )5 d% belo& the gain athe ma*imum transmitted signal po&er for a private!line cis 0 d%m


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FACILIT PARAMETERS +acility parameters represent potential impairments to a data signahey include the follo&ing,

)--(!#$ variation

!message noise

/mpulse noise

ain hits and dropouts

phase hits phase 1itters

Single frequency interference

frequency shift

phase intercept distortion

eak!to!average ratio


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!OO4"H# VARIATION

he telephone industry has established )00( #$the standard test!tone frequency.

he )00(!#$ channel loss for a private!line datacircuit is typically )6 d%.

3ong!term variations in the gain of the transmisfacility are called )00(!#$ variation and should ne*ceed 4( d%.


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C"MESSA$E NOISE

!message noise measurementsdetermine the average &eightedrms noise po&er.

!message noise measurementsare the terminated rms po&erreadings at the receive end of acircuit &ith the transmit endterminated in the characteristicimpedance of the telephone line.


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IMPULSE NOISE

/mpulse noise ischaracteri$ed by high!amplitude peaksimpulses of shortduration having an

appro*imately 7atfrequency spectrum.

he primary cause ofimpulse noise is man!madesources8 such as

interference from ac po&erlines8 transients from


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$AIN HITS AND DROPOUTS

9 gain hit is a sudden8random change in the gainof a circuit resulting in atemporary change in thesignal level.

he primary cause of gainhits is noise transientsimpulses on transmissionfacilities.

9 dropout is a decrease in

circuit gain i.e.8 signallevel of more than )2 d%


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PHASE HITS

hase hits slips aresudden8 random changesin the phase of a signal.

hase hits are classi'edas temporary variationsin the phase of a signallasting longer than ( ms.


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PHASE JITTER

hase 1itter is a form ofincidental phasemodulation! a continuous8uncontrolled variation inthe $ero crossings of asignal.

enerally8 phase 1itteroccurs at a "00!#$ rate or

lo&er8 and its primarycause is lo&!fre uenc ac


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FRE%UENC SHIFT

+requency shift is &henthe frequency of a signalchanges duringtransmission.

9nalog transmissionsystems used bytelephone companiesrequire coherentdemodulation and forthis the receiver should

be synchronous.


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SIN$LE FRE%UENCINTERFERENCE

Single!frequencyinterference is the presence of one or morecontinuous8 un&antedtones &ithin a messagechannel.

Spurious tones aremeasured by terminatingthe transmit end of acircuit and then

observing the channel


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PHASE INTERCEPTDISTORTION

hase intercept distortion occurs in cohereSS%S systems8 such as those usingfrequency division multiple*ing &hen thereceived carrier is not reinserted &ith the

e*act phase relationship to the receivedsignal as the transmit carrier possessed.


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PEA&"TO"AVERA$E RATIO

9 signal containing a series of distinctly shaped pulses &ith a high peak voltage!to!average voltaratio is transmitted.

3o& peak!to!average ratios indicate the presenc

di:erential delay distortion.9; measurements are less sensitive to attenuadistortion than

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Transmission Parameters (Facility & Interface Parameters)