1. What is the difference between the ISDN/ADSL and TLB-HT translators ?

The case's characteristics are identical. However, condensers are added to the primary and secondary circuits in order not to short-circuit the 96V DC. A shielded supply can be added on the user side if needed.


2. Can a digital phone be protected with a simple translator ?

No, a simple translator would short-circuit the telephone line. A security translator for pulse and frequency selection must be installed. This allows the reconstruction of the fork contact on the line side, and the transmission of the dialling selection and the ringing frequency.


3. I have connected two pairs on the primary and secondary side in order to use both half-coils, but the transmission is practically impossible.

The translator can only be used to protect one pair. By connecting two pairs, the transmission cannot be achieved because of the crosstalk caused by the links between both half-coils.


4. A link with a telephone wire must be protected by translators. The carrier frequency is 40 kHz. Which translator impedance should be chosen, 600 ohm or 150 ohm ?

The phone wire has a very fluctuating impedance level at low frequency, about 3000 ohm at 100Hz, falling to about 150 ohm at 10kHz, depending on the wire construction. The impedance level is stable at a higher frequency, at about 150 ohm. The impedance of 600 ohm was chosen so as to represent the best compromise in the band between 300 and 3500 Hz. In your case the stable part of the impedance level has already been reached, you must therefore choose a 150 ohm model, type TLB.


5. What is the purpose of the electrostatic screen between the primary and secondary on certain models ?

Its purpose is to eliminate the capacitive coupling between the primary and secondary, it therefore reduces the interference on the line, which is specially important for analog telephone links.