Instructions

PSI-MODEMSHDSL/SERIAL
4-2
PHOENIX CONTACT 104275_en_c00
4.2 Increasing immunity to interference
If the SHDSL cables are subject to strong external sources of interference, you should fur-
ther increase the immunity to interference of data transmission. This means that the lower
the SHDSL data rate, the higher the immunity to interference.
Formulas for determining the SHDSL data rate which offers the best possible immu-
nity to interference
There are two formulas for an SHDSL serial device. Which of the two formulas is appropri-
ate depends on whether serial data transmission is character or frame based.
1. Character-based transmission (standard)
SHDSL data rate
Maximum immunity to interference
= Data rate
Serial x
1.34 + 8 kbps
2. Frame-based transmission
SHDSL data rate
Maximum immunity to interference
= Data rate
Serial x
4.76 + 8 kbps
You must set this SHDSL data rate manually. Proceed as follows:
• Set the DSL data rate to "manual" (see "Step 3: DSL line configuration" on page 3-6).
• Enter the SHDSL data rate you require.
Use the lowest possible serial data rate that your application permits.
The lower the serial data rate, the better the immunity to interference.
Example (formula for "character-based transmission")
Calculate new SHDSL data rate for maximum immunity to interference
Check
The lower the serial data rate, the lower the required SHDSL data rate and the more im-
mune the system is to interference.
Therefore, for your application, select the lowest possible serial data rate.
SHDSL line 100 m
Cable diameter 1.4 mm (1.539 mm²)
SHDSL data rate calculated by the configuration software 10,714 kbps
Lowest possible serial data rate (application-specific) 500 kbps
SHDSL data rate
Maximum immunity to interference
500 kbps
x
1.34 +
8kbps
678 kbps
SHDSL data rate calculated by the configuration software 10,714 kbps
SHDSL data rate
Maximum immunity to interference
678 kbps
SHDSL data rate
Maximum immunity to interference
should be less than the automatically
determined data rate.
Your calculated SHDSL data rate
Maximum immunity to interference
must always be less than
the SHDSL data rate calculated by the configuration software.
If the SHDSL data rate
Maximum immunity to interference
is greater than the configuration soft-
ware data rate, you must reduce the serial data rate.