Pulse transformers

The SEDLBAUER standard transmitter program complies with the full range of needs in wired communications engineering in the reflection-free interconnection of sub-elements of a complex system.

As special technical requirements cannot be met with the standard transformer program, we also develop transformers according to customer specifications. We will gladly advise you on planning and project configuration.

For a quick and safe installation we offer complete solutions, e.g. consisting of: cable termination cabinets and racks, pre-assembled, pre-wired and tested transfer rails or transformers pre-mounted on special installation support frames.

Standard programme

The respective data sheet is stored after each item number.

Item number
Electric strength
Adaptation Z
0,3 - 6
6 - 2000
0,3 - 6
6 - 2000
0,3 - 6
6 - 2000
PCM-FLÜ2150:15025 - 210009
0,3 - 6
6 - 2000
o. Geh.
NFLÜ 3216600:6000,3 - 3,403
NFLÜ 322600:6000,3 - 3,401
NFLÜ 326600:6000,3 - 3,401
NFLÜ 3246600:600
0,3 - 3,403
NFLÜ 3272600:600
0,3 - 3,401
NFLÜ 32201:10,01 - 3,4
NFLÜ 3220600:3000,3 - 3,460
NFLÜ22000:50000,3 - 3,401
NFLÜ20600:6000,3 - 660
NFLÜ2500:6750,3 - 3,401
NFLÜ2600:3000,3 - 3,401
NFLÜ2600:12000,3 - 3,401
NFLÜ2600:6000,3 - 3,401
NFLÜ2450:12000,3 - 3,401
TFLÜ 5272150:130/150/1746 - 25201
TFLÜ 5272150:130/150/1746 - 25209
TFLÜ 5256150:130/1746 - 25201
TFLÜ 5252,5150:130/1746 - 25201
NFGÜ2600:2x6000,3 - 1503
NFGÜ2600:4x6000,3 - 1503
NFGS2600:2x6000,3 - 603
BBÜ20600:600/150:1500,3 - 6/6 - 25260

* Prepared for overvoltage protection plug (see accessories)
** Ringing voltage

Technical changes reserved


Item number
Product nameFigure
307 874Plug for overvoltage protection wire/ground, 230 V
310 345Adapter set for attaching transformers with design type 03 or 15 on support rail 35 mm - top-hat profile (1 set = 10 adapter pieces).
Assembly instructions
318 868 1Mounting plate for mounting 2 transformers of type 01/03 or type 14/15, incl. fastening material for installation in bays
310 8743HE transfer rail for reception of 6 transformers of type 01/03/14/15 for installation in 19" racks (with adapter in metric racks)
345 192Marking-strip holder with guide strip (suitable for mounting plate 318 868 1 and 318 388) for labelling and cable fixing
337 471Mounting plate for transformer type 01/03 with accessories
319 554Double plug 6463F with 2 ÜSAG 230V with strand 150 mm and extend. plug

Inspection record

According to the data sheet, different attenuation values of the transformer are measured and the electric strength is checked. They as such represent a quality standard. In the following, the individual terms are explained:

Transmission ratio:

The ratio of the primary-side to the secondary-side matching resistance of the transformer.

Adaptation [Ω]:

The theoretical resistance value of the transformer in the required frequency range, which optimally "matches" the two line sections to be connected to their characteristic impedance.

Ringing voltage [V]:

If, in addition to the working frequency range, the transmitter can also transmit the signalling frequency of the ringing pulses (25 Hz) with the corresponding voltage (for example 60 V), this property is specified explicitly.

Effective attenuation [dB]:

The measure of transformer losses in the operating frequency range.

Error attenuation [dB] (or reflection attenuation):

The measure of the quality of the resistance adjustment in the operating frequency range.

Symmetry attenuation [dB] (or near-end-crosstalk attenuation):

The measure of the equality of the two winding halves of the primary and secondary windings.

Electric strength [kV]:

The measure of resistance to short-term surges.


We assure that the guidelines of the German Institute for Standardization (DIN) and the German Electrical Engineering Association (VDE) have been complied with during the development and construction of our transformers.

Technical information

The field of application of transformers is exclusively wired transmission technology - wherever adaptation in relation to the different characteristic impedances of individual line sections has to be made, where galvanic separation of line sections has to be made or where so-called ‘phantom circuits’ (the multiple use of cable conductors) have to be applied. With wired transmission technology there are no alternatives to the transformer, so there are no advantages or disadvantages.

Transformers also serve:

  • for adapting balanced cables to coaxial cables

  • to terminate symmetrical earth or aerial cables

  • as low-pass (frequencies of the near-end crosstalk are blocked)

  • for the hybrid termination circuit (the coupling of a four-wire cable with a two-wire cable)

  • for power

Transformer switching symbol:

Transformer application class: HSG (according to DIN 40040)

H: Lower-limit temperature -25°C

S: Upper-limit temperature +70°C

G: Limit of rel. annual average humidity <65% (note: no condensation)

Galvanic isolation

For safety reasons, the electrical isolation of the two windings is important for security reasons in order to protect users and devices (modems, SCADA, smart meters, etc.) from over-voltages. Such voltages are caused e.g. by lightning strikes or power lines parallel to telecommunication cables. The frequencies can of course be transmitted despite galvanic isolation. 

Characteristic impedance

The characteristic impedance (or wave impedance) is independent of the line length, but it is usually frequency-dependent (dispersion). Frequency dependence is caused by the dielectric of the cable and has to be considered in broadband signal transmissions. The characteristic impedance should not be confused with the ohmic resistance, which describes the (thermal) losses when a current flows through the line. The line characteristic resistance can be conceived as the input resistance of an infinitely long, homogeneous line on which no reflection can occur.

Operating frequency range

The transformer is used in this frequency range (or in this bandwidth). Depending on the characteristic impedance, the transformer can only be used for a specific frequency range. These are to be taken from the data sheet. Typical value for an NFLÜ: 0,3 – 3,4 kHz

Phantom circuits

A method for increasing the number of speech channels. Two double lines (with the same electrical constants) are connected to each other in such a way that a third telephone circuit (phantom circuit) is created.

Remote power supply

Similar to the phantom circuit, the centre tap is used here for DC power supply / decoupling. Thus, for example, a regenerator can be operated without an external power connection to amplify data over a longer range.

Near-end crosstalk

The unwanted transmission of message energy from one transmission path to another. 

Hybrid termination circuit

Echo compensation, for separating the sending and reception directions.

Impedance matching

Synonym for resistance adjustment. Lines and transmitters can have different resistances, which can lead to power losses without adaptation. Since low energy is transmitted in the telecommunications sector, adaptation plays a particularly important role here.


The inductance coating can be increased by additional coils or high-permeable wrappings of the line. This allows longer cable lengths for the distortion-free transmission of low frequencies. Due to the increased inductance, there is also bandwidth limitation, since the spooling of the line acts as a low-pass filter.


PCM (Pulse-Code Modulation)

To suppress noises occurring along the transmission path, there is the possibility of using time-division multiplexer systems instead of carrier-frequency systems. In PCM, the amplitude values of the input signal are transmitted as a digital message and the analog value is reconstructed from the message at the output.



NFLÜLow frequency - Trunk line transformer
TFLÜCarrier frequency - Trunk line transformer
PCM-FLÜPCM - Trunk line transformer

Design solutions

Here is an overview of the standard designs of our transformers:


What do I need a transformer for?

Mainly it serves for galvanic isolation. Therewith, service employees or devices on the secondary side are protected against high voltages. Furthermore, the adjustment is of course in the foreground. An optimal adaptation reduces reflections and transmission losses.

How can I additionally protect my devices on the secondary side?

By the use of surge arresters which we offer as double connectors in accessories, the devices are optimally protected.


I need a transformer for special adjustments or with a special housing. However, I could not find anything suitable in the transformer standard programme on your homepage.

In order to keep the list well organised, not all types have been listed. We are happy to check if we have a suitable product for your application.


Can a transformer be used by swapping the connections to achieve a reverse-match ratio?

No. In general, a transformer should only be used for the applications that correspond to the use described in the data sheet.


What is the function of a shield winding in transformers?

This winding protects the transformer additionally from higher-frequency interferences, or capacitive couplings are suppressed. The shield winding between the primary and secondary windings is connected to ground on one side, so it must not be closed. Without a ground connection, the additional shield winding can even have a negative effect. This shield winding is explicitly stated in the data sheet. Not all transformers are equipped with it.

Can the transformer also be attached to a top-hat rail (TS35)?

Yes. With our adapter (Part No. 310345), a transformer of type 03 or 15 can be attached to top-hat rails. The adapter set can be found in our accessories catalogue.

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