Band Pass Filters; Circuit Description; Figure 10 Bpf Schematic; Figure 11 Completed Bpf - ozQRP MST3 Construction And Operation Manual

8 B P F
AND ASS ILTERS
8.1 C
IRCUIT DESCRIPTION
The bandpass filters are a two pole type with a Butterworth response and top coupled with a
small capacitor (C3). One end (T1) is link coupled to provide a balanced termination, while the
other end is capacitively coupled to 50 ohms by C4. Fixed capacitors C1 and C2 resonate with T1
and L2, while trimmer capacitors TC1 and TC2 allow fine adjustment of the centre frequency.
The schematic is shown in Figure 10, and a completed BPF is shown in Figure 11.
All coils are wound on T37 iron powder toroids. Type 2 (Red) is used for the lower bands while
Type 6 (Yellow) is used for the higher bands. All fixed capacitors are ceramic disc.
The TX and RX bandpass filters for each band are identical apart from the number of turns on
the coupling winding of T1. This is done to match the different impedance of the TX and RX
mixers.

Figure 10 BPF schematic

Figure 11 Completed BPF

MST3 Construction and Operation Manual – Issue 1 Page 38