Step attenuator

To impinge a HF signal with any configurable attenuation, whose chronological sequence is adjustable, the “USB Step Attenuator” was developed. The “USB Step Attenuator” contains up to three channels, which can be impinged with a configurable attenuation individually.
These different attenuations can be controlled independently. Each channel can be impinged by an attenuation between 0 and 31.5 dB with an increment of 0.5 dB. The accuracy is 0.1 dB. Digital step attenuators (ZX76-31R5-PP+) of the firm Mini Circuits are used.

The “USB Step Attenuator” can be powered by a 12V power supply, which is shipped with the device. As an alternative the 12V may be feed externally via banana plugs.

The attached DC part is measured by using the internal microcontroller. Three different levels were differentiated:

    • 1V to 2V
    • 5V to 6V
    • 8V to 14V

The visualization of the three voltage ranges is realized by LEDs at the front panel. The channel is charged in accordance with the voltage.

    • 1V to 2V / charge 10mA (+/- 1mA)
    • 5V to 6V / charge 30mA (+/- 3mA) 
    • 8V to 14V / charge 30mA (+/- 3mA)

Following block diagram shows the wiring of a channel:

 

The “USB Step Attenuator” may be controlled offline or via a control computer (online modus). In offline mode the previously configured attenuation curves may be executed individually per channel. The resolution is 0.5 seconds and the run time can be up to 24 hours.

The control of the “USB Step Attenuator” takes place by USB. The control and the definition of the attenuation curve are realized by a separate application. With this application, it is possible to enter, visualize and change the attenuation curves. All attenuation curves are saved as an XML file and may be loaded on demand. The application is currently available for Windows (32/64-Bit).

The application allows programming of any attenuation curves. For this purpose the individual values may be entered manually or may be generated by predefined functions (e.g. sine wave). The resolution of the curve is adapted during the transfer to the “USB Step Attenuator”.