Tagged: band pass filter

SignalSurge – An open source bandpass filter with selectable LNA for the VHF and UHF bands

Thank you to Rodrigo Freire for writing to us and sharing his project called 'SignalSurge'. The SignalSurge project started when Rodrigo discovered that adding an RTL-SDR Blog FM Bandstop filter to his Yaesu FT-991A significantly improved his reception in the 2-meter band.

An FM bandstop filter can improve reception by reducing the power of strong broadcast FM signals, which can overload the front end of radios, causing the desensitization of signals on other bands.

This finding led Rodrigo to design SignalSurge, a bandpass filter for VHF and UHF bands, with a selectable LNA. The design includes selectable 2m and 70cm bandpass filters, a selectable 15dB LNA, automatic LNA shutdown when the radio is transmitting, and ESD protection. A 50W relay gives the ability to select between filters and switch the LNA in or out.

The design is entirely open source and available on the SignalSurge GitHub.

SignalSurge Schematic
SignalSurge Schematic

Building a DIY 137 MHz Band Pass Filter

Over on YouTube Adam 9A4QV has uploaded a video showing how to build a DIY bandpass filter for 137 MHz. This can help improve the reception of NOAA and Meteor M weather satellites, by blocking strong out of band signals. Adams design is a 132 MHz – 142 MHz Butterworth bandpass filter which gives about 35 dB attenuation outside of the pass band. He’s also posted a write up documenting the filter design on his website.

Lucas Teske recently went ahead and built the 137 MHz filter suggested by Adam. Lucas didn’t have the correct capacitor values so he ended up cascading several in series. His results showed that the filter did improve his reception significantly.