fm95

FM95 is a audio processor for FM, it does:

• Pre-Emphasis
• Low Pass Filtering
• AGC
• Stereo (Polar too)
• SCA
• BS412 (mpx power limiter, simplest implementation ever)

Supports these inputs:

• Audio (via Pulse)
• MPX (via Pulse, basically passthrough, i don't recommend this unless you have something else than rds or sca to modulate, you could run chimer95 via here)
• RDS (via Pulse, expects unmodulated RDS, rds95 is recommended here, in modulation this is quadrature to the pilot, number of channels is specified by the argument, each of the channels (max 4) go on these freqs: 57, 66.5, 71.25, 76)
• SCA (via Pulse, by default on 67 khz with a 7 khz deviation)

and one output:

• MPX (via Pulse)

How to compile?

Note that you're required also to load submodules, if you don't know what that means, ask ChatGPT

To compile you need cmake, liquid-dsp and libpulse-dev, if you have those then do these commands:

mkdir build
cd build
cmake ..
make

Done!

CPU Usage?

Should run completly fine on a pi 5, fine on a pi 3b (30% cpu, 45% with lpf)

Other Apps

FM95 also includes some other apps, such as chimer95 which generates GTS tones each half hour, and dcf95 which creates a DCF77 compatible signal, and vban95 now which is a buffered VBAN receiver

FM95 Calibration

FM95 features a calibration mode -V which instead of outputing the MPX just outputs a 400 hz tone, use that tone to match the deviation on your transmitter

Usage of other projects

The apps use inih by Ben Hoyt.