Schwarzbeck SY 9223-120B Broadband Balun 50Ω - 120Ω

The balun transforms an unsymmetrical signal at a 50 Ω source impedance into a galvanically isolated symmetrical signal at 120 Ω impedance in a wide frequency range.

Thus measurements on symmetrical quadripoles which have an impedance of 120 Ω can be done using regular measurement devices which work with a 50 Ω impedance usually.

For instance the response characteristic of VDSL2+ lines can be determined with the SYS9223-120B. Also measurements according to CISPR 17 (resp. DIN EN 55017) can be performed on components or filters.

The device under test or equipment under test (DuT, EuT) can be connected to the SY9223-120B using a RJ45 jack or two 4 mm jacks.

The measurement device has to be connected to the BNC connector using a shielded coaxial cable.

Practically the device under test has to be measured in between two broadband baluns. To avoid to measure the own attenuation of the measurement setup one can normalize the setup in advance. Therefore connect the EuT sides of two baluns to each other and connect the BNC cables to the measurement ports of the baluns.

Since the ripple is very low it will be sufficient to use the insertion loss of 10 dB per balun as stated in this data sheet.

Please note: the attenuation values refer to the transmitted power. Since an impedance transformation takes place the different reference resistor value has to be considered when measuring voltage or current.

So a signal of 1 V at a 50 Ω input (which equates 13 dBm or 20 mW) results in a power of 3 dBm (2 mW) after the 10 dB attenuation. This equates to a voltage of 490 mV (-6.2 dBV) at 120 Ω.

Besides this 120 Ω model there are broadband baluns available for 100 Ω, 135 Ω and 150 Ω from the SY9223 series.

The measurement setup should be placed on an isolated plane.

Frequency [MHz]

Fig. 1: Transmission of two SY9223-120B connected at the EuT port

Frequency [MHz]

Fig. 2: Return loss of SY9223-120B (EuT terminated with 120 Ω)