P25 Receive tuning

ADC levels have overflowed
P25RX: pos/neg/centre/threshold 223 -189 17 206
P25RX: sync found in Ldu pos/centre/threshold 2580 -28 184
P25, LDU2 audio, errs: 131/1233
P25RX: sync timed out, lost lock
P25, received RF end of transmission, 2.5 seconds, BER: 3.3%

If ADC overflow messages come up during normal P25 talking, the level into the modem cpu from the ZUM/NTH board is too high. It is not unusual to have it happen at the end of a PTT when you are running pretty hot receive audio. The 206 on the end of the P25RX frame is also a little higher than I see on my system when it is aligned well. Mine is more like 135. If the MMDVM.ini rx level digital pot is higher than 75 I also see these two telltales on my test system. The capture buffer is 1233 frames. 131/1233 means 131 error packets in the 1233 string. You want to get that to zero or as close as possible on the bench as it only gets worse in real world operation with weak signals etc. Sync timed out lost lock is normal at end of PTT. BER of 3.3% means you have more tuning to do. Your receive is too high is my best analysis. The modems have limited tuning ranges and may be over-driven in the first place, so sometimes it is difficult to see where the overdrive is. An oscilloscope makes this a lot easier if you can get access to one. Doug KD8B