Siemens SINAUT ST7 - Page 49

Mounting and Installation
6NH7811-0AA22 © Siemens AG 2002 All Rights Reserved
2-30 MD2 Modem (07/2002)
The values listed in Table 2-22 are approximate values and are based on the data
in Table 2-21.
A level reserve of 4 dB was included in the calculation of the maximum range. This
is to compensate for deviations in cable properties that experience has shown to
occur in actual operation, and thus always ensure that sufficient signal level is
available for undisturbed data transmission. To calculate the values listed in the
table the following formula was used:
[]
Cable
LTOPInsert
Cable
LTOPResSend
A
AA
NTP
A
ANNN
S
´+
´-
´--+
=
22
min
max
Legend:
A
Cable
Loss (Attenuation) per km of the used cable [in dB]
A
Insert
Insertion loss per tapping point [in dB]
A
LTOP
Loss per LTOP [in dB]
NTP Number of tapping points
N
min
Minimum receive level [in dB]
(-43 dB for MD2, enter only absolute value in formula)
N
Send
Send level [in dB]
(normally –6 dB or 0 dB)
N
Res
Level reserve [in dB]
(4 dB was calculated in Table 2-22)
S
max
Maximum range [in km]
Calculation example:
For core diameter 0.8 mm, at 2400 bps, with LTOPs and send level –6 dB
[]
4,1
4,022,0
4,1
4,024)6(43
max
´+
´-
´---+-
= NTPS
4,1
8,02,0
4,1
8,04643
max
+
´-
---
= NTPS
4,1
0,1
4,1
2,32
max
´-= NTPS 8,023
max
´-= NTPS
Using the above formula the user can make his own calculations if the data of the
cable actually used are known.
There is no need to calculate the maximum range for telecom leased lines. The
telecom is responsible for providing a sufficient signal level. Recommended cable
quality for telecom leased lines:
Analog fixed line connections, type M.1020 or M.1025.