n11. Curing EMC problems -
without causing bit error or syncloss

This page is under preparation

Representative audio line transformer in the 'kg'-class with good reputation.
NFLÜ 32.

Transformers for 2MB HDB3 line code. The first is 4x 10 turns (witstand 20kV spark), and the second is 2x 20turns and withstand 40kV spark
Have used several douzens for 2.048Mbit/s PCM regenerator systems on 120 ohm line impedance, and some with less turns for 75 ohm circuits
Ferrite core: Siemens B64290-K618-X27 25mm OD.

The 2nd type is also suggested for ADSL, and could have somewhat less turns than PCM (HDB3)), while HDSL and ISDN require larger
transformers which has not been available for me, but I can only rely of experience from another person in this area.

Spectrum for ADSL: from ca 140kHz up towards 1,1 MHz

1) Principal 1:1 transformer

usually 600 ohm or 120 ohm line impedance
1a) A 1:1 transformer with separate secondary and
primary divided into two sets of windings
2) Rewiring a 600 : 1100* ohm transformer (1:1,83 ratio)
to work as a 1:1 ratio type (600 :600 W)

The insulation voltage may not be so high as in the first place.

*) 1100 ohm was only for ancient pupinized long distance
telephone line systems, and has no relevance today, it is
rather more a tragedy if such line still exist.
3) Audio/LF choke to cure common mode noise on
telephone lines and improve balance to reduce hum level
from mains fields on the telephone lines near power stations or
other installations
4) Audio choke used to improve power feed noise
on HDB3 2MBit/s line systems. The choke could be
a 600:1100 ohm transformer rewired as 1:1 type, see
note above.

Requirement for 2MBit/s is 5-6kHz minimum frequencies
to pass through the ferrite transformer. Line impedance 120ohm

It seems to be the same configuration between the NT-box and
ISDN application unit and using AMI code, frequency limit is
lower than for 2MBit/s HDB3 codes.

Transformer for 2B1Q line code (HDSL or ISDN*) with power feed, one such arrangement per pair of wires.
The ferrite transformer must pass somewhat lower frequencies that HDB3

*) It is also possible to arrange a different mode ISDN which is used for power stations where line transformers are a must.


Expected block functions and frequency requirements for ADSL and ISDN, suggested extra transformer for lightening protection..
Spectrum for ADSL: from ca 140kHz up towards 1,1 MHz, while it seems to be 0.5-120kHz for ISDN, but I don't know for sure.


Last update: 2004.07.14