RT-880 nicFW's First "Real" APRS Packet
Added 2025-10-02 15:42:54 +0000 UTCYet to be tested before release.
Comments
Love it
M0FXB HAM RADIO DIARY
2025-10-03 13:54:51 +0000 UTCstd::array crc compute_crc(std::begin(packet_data), std::end(packet_data)); // Insert CRC at the end of the frame std::vector frame_bytes(std::begin(packet_data), std::end (packet_data)); frame_bytes.insert(frame_bytes.end(), {crc[0], crc[1] }); // Convert the frame bytes to a LS8 bitstream std::vectorsuint8_t> frame_bits; frame_bits.reserve(frame_bytes.size() 8); bytes_to_bits(frame_bytes.begin(), frame_bytes.end(), std::back_inserter (frame_bits)); // Bit stuffing std::vector stuffed_bits; bit_stuff(frame_bits.begin(), frame_bits.end(), std::back_inserter(stuffed_bits)); // Build complete bitstream: preamble data + postamble // Preamble: 45 HDLC Flags (0x7E = 01111110) // Postamble: 3 HDLC Flags std::vector bitstream; add_hdlc_flags(std::back_inserter(bitstream), 45); bitstream.insert(bitstream.end(), stuffed_bits.begin(), stuffed_bits.end()); add_hdl.c_flags(std::back_inserter (bitstream), 3); // NRZI encoding of the bitstream nrzi_encode(bitstream.begin(), bitstream.end()); //AFSK modulation std::vector audio_stream; int sample_rate = 48000; dds_afsk_modulator modulator(1200.0, 2200.0, 1200, sample_rate, 0.88); double silence_duration = 1.0; // seconds int silence_samples = static_cast(silence_duration sample_rate); // 1 second at 48kHz int signal samples = bitstream.size() modulator.samples_per_bit(); audio_stream.resize(silence_samples + signal samples); int write_pos = silence_samples; for (uint8_t bit bitstream) for (int i = 0; i < modulator.samples_per_bit(); ++i) { audio_stream [write_pos++] = modulator.modulate(bit); apply preemphasis (audio_stream.begin() + silence_samples, audio_stream.end(), sample_rate, /tau/75e-6); apply_gain(audio_stream.begin() + silence_samples, audio_stream.end(), 8.3); // scale to 30% volume insert_silence(audio_stream.begin(), sample_rate, silence_duration);
Daniel
2025-10-03 03:54:45 +0000 UTCI found the following code snippet by chance on Facebook which claims to explain APRS/AFSK in 60 lines, just in case it is of any help:
Daniel
2025-10-03 03:54:12 +0000 UTChttps://github.com/wb2osz/direwolf
medal.bricks
2025-10-02 16:48:09 +0000 UTCCopy, I’ll try again when able. I’ve used a few APRS programs on PC, and I believe at least one of them allows for diagnostics. I’ll double check, but the best is “Yakk”
medal.bricks
2025-10-02 16:43:06 +0000 UTCReally excited seeing all the progress with APRS! Can’t wait to be able to send messages to my VR N76 when this is fully fleshed out
Nathan Philip
2025-10-02 16:30:07 +0000 UTCI did enode a full test APRS message, but I could have made a hundred mistakes. I really need something that lets me analyze it.
Marcus Dudley
2025-10-02 16:05:47 +0000 UTCThat sounds EXACTLY like APRS. I did try to decode it with the aprs .fi app, and it didn’t decode, but I’m also working on so the volume was pretty low. Did you actually encode an APRS message? Or was that just tones which sound like APRS?
medal.bricks
2025-10-02 16:03:13 +0000 UTC
