Raspberry Pi Vs RTCM

App_rpt-users
1

Hello, so I’m getting ready to setup a multi receive system with one transmitter. Do I have to use a RTCM still or can I use a raspi for that instead? Any info would be appriciated!

Thanks,
KF0QDL

2

For a RTCM voting system you need:

  • One computer. Either a RPi or AMD64.
  • An RTCM at each radio site and one at the computer.
  • The RTCM at the computer must be on the same LAN segment and can be shared with a radio.
  • A GPS for each RTCM to provide 1PPS.
1 Like
3

So do I need the gps? There is only going to be one transmitter and like 3-4 receive only sites. That’s why I was curious if I even needed the RTCM.

4

For real voting with chan_voter, yes you must use RTCMs or VOTERs with GPS units connected to each client.

Or, you can use Simple Voter which would use Pi’s (or PCs, etc) instead of RTCMs / VOTERs, and would also not require GPS hardware. However, there will be an audibly noticeable change whenever the receivers switch - which could be several times per second depending on the system, architecture, geography, users, etc - it’s a trade-off.

1 Like
5

As @Mason10198 mentioned, you can go with a simple voter. I don’t think that’s a viable option because your users won’t be happy.

Here are some points to consider when setting up a voting system:

  • The GPS 1PPS (one pulse / second) is needed for synchronization.
  • Each receive packet contains the following: The computer uses this information to align and vote for the strongest signal.
    • 80ms of audio
    • An RSSI value of 0 to 255 (derived from the noise/squelch circuit)
    • A precise time stamp from the GPS
  • The receivers need to have a discriminator output with noise above 3Khz or so for RSSI and squelch. Digital radios typically do not have a real discriminator output. The Motorola SLR5000 is one example that won’t work for RTCM voting. The Motorola Quantar works only because there is code in the RTCM to filter voice peaks out of its inadequate noise bandpass.