The QSF-06 is a freely configurable pre-selector with up to six switchable filters. The automatic control is designed for use with the FDM-DUO transceiver, but could be adapted to any other radio as well. The QSF-06 uses the same filter boards which are already available for the FDM-DUO-R SDR receiver. This includes empty prototyping boards for own filter designs.
The enclosure of the QSF-06 has the same size and design as the FDM-DUO qrp transceiver and therefore also fits optically very nicely. When shipped no filter is installed (except a "by pass" board). The user has to equip the preselector with up to six filters of his or her choice. Filters exist as high or low pass for long and medium wave, as well as band filters for the ham radio bands on shortwave.
The filter selection is driven via the "EXT I/O" port of the FDM-DUO, a suitable cable is provided with the QSF-06. The transmit/receive relay switches the filter into the signal path only on reception. A configuration of the filter selection in the "FDM-DUO Manager" software is required once, so the software knows which filter to use when. The QSF-06 includes all cables required for use of the preselector with the FDM-DUO.