📄 7_3_01.txt
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unanimously declares the view
that Group 1 facsimile apparatus for use on the general
switched telephone network and international leased circuits should
be designed and operated according to the following standards:
1 Scanning track
The message area should be scanned in the same direction in
the transmitter and receiver. Viewing the message area in a verti-
cal plane, the scanning direction should be from left to right, and
subsequent scans should be adjacent and below the previous scan.
2 Index of cooperation
The nominal index of cooperation is 264. In cases where a
lower vertical resolution is acceptable, and by agreement between
the users, an optional index of cooperation of 176 may be used.
These values should be observed with a nominal tolerance of _
| % for each equipment.
3 Dimensions of apparatus
3.1 The apparatus should accept documents up to a minimum of
ISO A4 size (nominally 210 mm x 297 mm).
3.2 The total scanning line length ( active sector plus dead
sector) should be nominally 215 mm. Nominally 200 mm should be
available for scanning or recording, the remainder being the dead
sector
3.3 For any one document the nominal number of scans should
be 1144 for an index of cooperation of 264 (762 scans for an index
of 176). The receiver should be capable of recording nominally
1144 scans per document for an index of cooperation of 264 (or
762 scans for an index of 176).
3.4 Apparatus with other dimensions may be used provided that
the index of cooperation is respected, that the total scanning line
length lies between 210 and 250 mm and the usable recording line
length retains the same ratio to the total scanning line length.
4 Scanning density
Scanning density is normally 3.85 lines per mm.
5 Scanning line frequency
In the subscriber-to-subscriber service via the general
switched telephone network, the scanning line frequency should be
180 lines per minute (see Note).
For leased circuits operation the best line frequency, which
may be higher or lower than 180 lines per minute, may be chosen
according to the circuit characteristics.
The scanning line frequency during the transmission should be
kept within _ | 0 parts in 106 of the nominal value.
Note - With manual control at the two ends of connection set
up over the general switched telephone network, another scanning
line frequency (e.g. 240 per minute) may be chosen by agreement
between the two operators.
6 Phasing
The duration of the phasing signal for transmitters should be
15 _ 1 seconds.
In a preferred method of phasing (see Note 1), the transmitter
sends a series of alternating white and black signals in such a way
that the white pulse (phasing pulse) is 4 to 6% of the total scan-
ning line length and the leading edge is 2 to 3% in advance of the
middle of the dead sector.
Receiving apparatus should synchronize the middle of its dead
sector 0.5 to 4.5% lagging the leading edge of the received phasing
pulse (see Note 2).
Note 1 - In a permitted method of phasing for present genera-
tion machines, the transmitter sends a series of white and black
signals in such a way that the white pulse is 2 to 12% of the total
scanning line length and the leading edge is 2 to 3% in advance of
the middle of the dead sector.
Note 2 - Maximum reduction of recorded scanning line length
due to synchronizing misalignment should not exceed 3% of total
scanning line length. Maximum reduction of recorded scanning line
length due to the combined effect of deviations of the transmitter
and receiver scanning line frequencies should not exceed 4% of
total scanning line length. The effect of these reductions of
recorded scanning line length may cause it to be less than the nom-
inal 200 mm.
7 Modulation and demodulation equipments
7.1 Amplitude modulation | (for leased circuits only)
The facsimile signal level is higher for black and lower for
white.
The carrier frequency should range between 1300 and 1900 Hz
and will depend upon the characteristics of the circuits used.
7.2 Frequency modulation | (for leased circuits and for
switched connections)
The frequency corresponding to black will normally
be f0 + 400 Hz and the frequency corresponding to white will nor-
mally be f0 - 400 Hz (see Note).
For switched connections f0 = 1700 Hz (provisional). For
leased circuits f0should range between 1300 and 1900 Hz: the choice
of the centre frequency f0will depend upon the circuit characteris-
tics. However, if the user, in some cases, wishes to use the
apparatus on switched connections, f0 = 1700 Hz.
The stability of the transmitter must be such that the signi-
ficant frequencies do not vary by more than 32 Hz from their nomi-
nal value in a period of 15 minutes.
Note - Attention is drawn to the fact that there are some
equipments currently in operation for which black and white ele-
ments are represented in the opposite sense, but the preferred
standard for new equipment is as indicated above.
7.3 Power at the transmitter output
When amplitude modulation is used, the power of black at the
transmitter output must be able to be adjusted between -7 dBm and
0 dBm. The white level must be approximately 15 dB below the black
level.
In frequency-modulated systems, the level at the output of the
facsimile apparatus must be able to be adjusted between -15 dBm and
0 dBm.
The equipment should be so designed that there is no possibil-
ity of this adjustment being tampered with by an operator.
7.4 Power at the receiver input
The facsimile receiver must be so designed that it functions
correctly when the input power ranges between 0 dBm and -40 dBm,
the latter value being considered provisional. In the case of
amplitude modulation, this concerns the power of the black signal.
No control of receiver sensitivity should be provided for operator
use.
Recommendation T.3
STANDARDIZATION OF GROUP 2 FACSIMILE APPARATUS |
FOR DOCUMENT TRANSMISSION
(Geneva, 1976; amended at Geneva, 1980)
The CCITT,
considering
(a) that Recommendation T.2 refers to Group 1 type apparatus
for ISO A4 document transmission in approximately six minutes;
(b) that there is a demand for Group 2 apparatus which enables
an ISO A4 document to be transmitted over a telephone-type circuit
in approximately three minutes;
(c) that the Group 2 apparatus reproduces document quality
similar to Group 1 apparatus;
(d) that such a service may be requested either alternatively
with telephone conversation, or when either or both stations are
not attended; in both cases, the facsimile operation will follow
Recommendation T.30;
(e) interconnection between two machines of different designs,
both conforming to Recommendation T.3 as published in the
Orange Book may give a lower guaranteed reproducible area in cer-
tain cases;
unanimously declares the view
that Group 2 facsimile apparatus for use on the general
switched telephone network and international leased circuits shall,
in future, be designed and operated in accordance with this Recom-
mendation. Apparatus conforming to Recommendation T.3 of the
Orange Book may continue in service.
1 Scanning track
The message area should be scanned in the same direction in
the transmitter and receiver. Viewing the message area in a verti-
cal plane, the scanning direction should be from left to right and
subsequent scans should be adjacent and below the previous scan.
In order to avoid loss of information, users should insert
documents so that the scanning direction is from the wider to the
narrower margin.
2 Dimensions of apparatus
The following dimensions are recommended but apparatus with
other dimensions may be used provided that the factor of coopera-
tion is respected and that the total scanning line length lies
between 215 and 222 mm.
Factor of cooperation (FOC) 829 _ 1%
Total scanning line-length (TLL) 215 mm
Usable scanning line-length (ULL) 205 mm minimum
The end of ULL shall lie between 0 and 1 mm within
the nominal position of the right hand edge of an ISO A4 size docu-
ment.
Input document size Up to a minimum of ISO A4 size
(nominally 210 x 297 mm)
The foregoing dimensions give rise to the following approxi-
mate secondary dimensions.
Index of cooperation (IOC) 264
Scanning density 3.85 line/mm
Number of scanning lines in a document 297 mm long
1145
3 Scanning line frequency
3.1 The scanning line frequency should be 360 lines per
minute.
Note - Another scanning line frequency (e.g. 300 lines per
minute) may be chosen by agreement between the two stations.
3.2 The scanning line frequency during the transmission should
be kept within _ | parts in 106 of the nominal value.
4 Phasing
For phasing prior to transmission of document information the
transmitter sends a signal as shown in Figure 1/T.3. The start of
the carrier indicates the end of the lost time time to the start of
carrier should be _ | .5% of TLL. The receiver should phase its
reference point with an accuracy of _ | % of TLL to this start of
the carrier. The reference point should be 209 mm before the end of
ULL (see Figure 2/T.3).
Note - In the case of the multiple page transmission the
phasing procedure may need to be repeated between pages.
Figure 1/T.3, (M) p.
Figure 2/T.3, (M) p.
5 Document transmission
5.1 During transmission of document information the
transmitter should transmit full amplitude carrier during the lost
time for at least 4% of the transmission time for TLL. The phase of
the carrier may be reversed at the end of this signal.
Following the lost time the information transmitted to the
receiver is the one contained in ULL. The value of ULL is defined
in S 2.
The receiver must be able to reproduce at least ULL on the
reproduction media after the end of the lost time.
5.2 This signal may be used at the receiver as an amplitude
reference independent of the document signal and also to indicate
to the receiver that document transmission is still in progress.
6 Paper alignment
All types of apparatus should be designed to ensure that paper
is positioned within _ | .5 mm of nominal in the horizontal direc-
tion. In the vertical direction it must be ensured that paper is
positioned in such a way that scanning and recording start not more
than 4 mm down the document from the top edge.
7 Modulation and demodulation
7.1 Equivalent modulated waveforms with vestigial sideband
amplitude modulation - phase modulation characteristics should be
used for Group 2 apparatus operated on leased circuits and on the
general switched telephone network. The carrier frequency should be
2100 _ 10 Hz (see Note). A white signal should be represented by
maximum carrier and a black signal by minimum (at least 26 dB below
white) or no carrier. The phase of the carrier representing white
may be reversed after each transition through black.
Note - It should be noted that there are equipments in ser-
vice using, inter alia, a carrier frequency of 2048 Hz.
7.2 The facsimile transmission could contain a limited range
of half-tones represented by a carrier amplitude less than that
sent during the lost time.
7.3 A vestigial sideband filter symmetrical about the 2100-Hz
carrier frequency should be provided at the transmitter. The
response of this filter should conform to Figure 3/T.3. The accu-
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