Block Diagram

Calculations

The duplexer is obtained putting together two separated filters:

  • high pass for 433 MHz
  • low pass for 144 MHz

i calculated the two filters separately using lc-filter-design-tool/.

See below the calculation for the 432 MHz high pass filter: note that I set the cutoff frequency at 400 MHz

and the 144 MHz low pass filter. Please note I set a 150 MHz cutoff.

Schematic and LTSpice simulation

Assembly

I used a small case 74 x 74 x 22 (H) mm

The 56 nH, 91 nH and 82 nH inductances are obtained with 4 turns of 1 mm enameled copper wire on a 6 mm diameter.

Their different values are set with different length (The higher the length the lower the inductance)

The 15 nH are 1 single turn of 1 mm enameled copper wire on a 4 mm diameter. 

Results

144 MHz side

  • insertion loss at 144 MHz = -0.5 dB
  • attenuation at 432 MHz = - 52 dB

432 MHz side

  • insertion loss at 432 MHz = -0.4 dB
  • attenuation at 144 MHz = - 45 dB