This document describes the design of a band pass filter for the 2 meter amateur radio band with low insertion loss. The filter uses surface mount capacitor and inductor components to create a band pass response that attenuates signals outside of the 2m band, including FM radio and TV bands, by at least 40 dB. It is intended to improve the performance of the author's 2m software defined radio receiver by reducing overload from out of band signals. Construction details are provided for building the filter using inexpensive surface mount components on a double sided printed circuit board.
Design For Accessibility: Getting it right from the start
2m bp filter yu1 lm
1. Band Pass Filter with Low Insertion
Loss for 2m
Dipl ing Tasić Siniša –Tasa YU1LM/QRP
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 is
input 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 smaller
size 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 diode
mixers 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 moderate
selectivity; FM and TV band are attenuated min 40 dB.
I wish you successfully 2 m band pass filter realization.
VY 73/72 and GL in SDR homebrew Tasa YU1LM/QRP
tasa@imtel-mikrotalasi.co.yu
stasic@eunet.yu
3. 0.044 0.094 0.144 0.194 0.244
Frequency (GHz)
TRANS
-80
-60
-40
-20
0
0.1377GHz
-3.63dB
0.1523GHz
-3.413 dB
0.1742 GHz
-41.16 dB
0.05028GHz
-69.11 dB
0.1079GHz
-45.03 dB
0.145GHz
-0.5083 dB
DB(|S(1,1)|)
BP2m
DB(|S(2,1)|)
BP2m
DB(|S(2,2)|)
BP2m
Amplitude frequency response for ideal C capacitors and real Q inductors
4. 0.044 0.094 0.144 0.194 0.244
Frequency (GHz)
TRANS
-80
-60
-40
-20
0
0.1375 GHz
-3.539 dB
0.1519 GHz
-3.592 dB
0.1742 GHz
-41.78 dB
0.05028 GHz
-69.1dB
0.1079GHz
-44.98 dB
0.145 GHz
-0.644 dB
DB(|S(1,1)|)
BP2m
DB(|S(2,1)|)
BP2m
DB(|S(2,2)|)
BP2m
Amplitude frequency response for real C capacitors from Murata and real Q inductors
L= self support isolated copper wire diameter 1mm (AVG18) wound at 5 mm 6 turn
close wound length 6mm Qo=350 and Frez=901 MHz.
5. Double side PCB (bottom side is completely copper side) dimension 50 x 20 mm
