The modification for suppress the spurious of this time is as follow. I hope this would be useful for you.
1) Add 3.3uF electrolytic capacitor and 0.1uF x 2 bypass capacitor to VCC line of Arduino board =>PIC1-1a PIC1-2a 2) Insert high frequency choke of about 100 uH in the power line of Arduino =>PIC2a 3) Connect the minus line of power supply line to the ground =>PIC3-1a PIC3-2a 4) Connect the minus line of BITX40s to the ground 5) Add 0.1 uF × 2 bypass capacitor to VDD of BITX 40 board=>PIC5a 6) To prevent common mode noise, add 0.01uF x 2 bypass capacitor to the power connector=>PIC6a
