A Bandpass Filter Pulls In The Signals

It’s an unfortunate side effect of proximity to a large transmitter that the received signal can overload a receiver’s front end even when tuned to other frequencies. [Rfrht]’s had this …. A Bandpass Filter Pulls In The Signals.

[Rfrht]’s had this problem with nearby FM broadcast transmissions overloading the 2 metre and 70 centimetre amateur bands. This allows the signals you want to pass through while rejecting or attenuating out-of-band frequencies. On board, aside from the filters themselves, are a low-noise preamplifier and relays to switch between receive and transmit.

Everything is controlled by logic-level signals. All components are surface-mount, and the PCB layout clearly takes special care with RF routing. We can honestly say there have been times in the past when we could have used this project.

Unfortunately, our filters, built Manhattan-style, weren’t anywhere near as elegant as this one.