multimon-ng used as demodulator, corrupts packet data - this igate must not be used on APRS-IS

[hessu]

https://github.com/cceremuga/pypacket/blob/5f6060311958104bfecedb135e15e241610d42e8/pypacket/implementations/multimon_decoder.py#L5

Hi,

multimon-ng AX.25 packet radio decoder output is not binary clean. It is designed for decoding packets for human-readable use, and it strips/modifies out some bytes (non-printable packets which do appear in some packet formats) and does not handle multi-line packets well. Using it on an iGate will cause modified duplicate packets to be generated on the APRS-IS, when other iGates forward an intact packet and this igate forwards a corrupted packet.

A far better strategy for creating an iGate with an RTL-SDR is doing FM demodulation with rtl_fm, and passing the audio stream to Direwolf which can either be configured to act as a standalone iGate, or used as a KISS TNC for another iGate software (I use it with aprx). This provides a proper, safe APRS implementation, which treats the packets the same way as other iGates on the network, without data corruption.

Please see https://github.com/hessu/aprsc/blob/main/doc/IGATE-HINTS.md for details.