★ Band Pass Filter with Low Insertion Loss for 2m (145Mhz) ★
This design is part of my VHF/UHF SDR receivers. The VHF /UHF receivers are assembled as “RF bricks”. The receiver is broad band design and determined with used mixer.
Input filter and local oscillator are determining receiving band. In some causes I am using preamplifier to improve receiver sensitivity also. This band pass filter is one of this bricks. It isinput filter for 2 m. It is very easily repetitive design but it is now realized with C SMT components. I didn’t try classic C size components but from some mine previously designs experience it is possible realization. One way is that capacitors are mounted from the ground(bottom) side. We can drill PCB for capacitors mounting and than capacitors leads solder from the top side. To prevent unwanted contacts with GND first we will drill PCB with borer smallersize for example 0.8 or 1 mm and than with borer 2.5-3 mm on the bottom GND side to remove copper surface only. The double side of PCB can be make as it is proposed with soldering the rest of resistor leads through the holes drilled between top and bottom PCB side. This is easy way how to make home made metallization of vias. I am recommending you that filter are mounting inside the some metal box or box made from soldered FR4 double side peaces.Filter is mounted at the front of the mine 2 m SDR receiver. Double balanced diodemixers are very sensitive to the very big number broad band input signals and harmonic receiving. The input band pass filter is improving IMD specification from receiver. The 2 meter receiver can be easily overload with out-band signals. The realized filter had moderateselectivity; FM and TV band are attenuated min 40 dB.I wish you successfully 2 m band pass filter realization. YU1LM / QRP
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