Today I’ve been working on the Cavity duplex filter for the new DMR-repeater. The exact frequency is yet unknown but I assume it will be 438.3125 MHz for the output and 430.7125 MHz for the input, which makes a -7.6 MHz shift.
I’m the lucky owner of a Rigol DSA815 Spectrum Analyzer (9 kHz – 1,5 GHz) with tracking generator onboard so the mandatory tools are available.
The goal was to have a path attenuation of maximum 3 dB and the minimum attenuation between the transceiver and receive frequency should be 80 dB which worked tough the Duplex filter brand is Guang Zhou China. It’s not a German Kathrein but since the shift is 7.6 MHz and not 1.6 MHz things become less critical.