To protect my 50 & 70 MHz transceiver against high RF from the HF station, the antennas are only separated 1 meter apart I designed a High Pass Filter with a cut-off frequency of 45 MHz. For this design I used the ELSIE software. You can find this super software HERE
The filter proofed to be working fine. The results were the following:
S21 50 MHz -0,4dB
S21 70 MHz -0,3dB
S21 30 MHz -42dB
S21 20 MHz -70dB
S11 50 – 70 MHz 20 – 25dB
Very nice results. Tuning is done by streching and pressing the inductors for best result.