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.
lowpass (1 dB attenuation, 90 dB separation)
highpass (1 dB attenuation, 90 dB separation)
