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This is a collection of notes I've captured on the MMDVM. Where possible I'll attribute the author. I make NO claim that I was the author. I will organize this when possible.

The pos number is an indication of the detected sync word position. Ideally it should remain constant. If it increments or decrements it is a sign of timing drift between the Arduino and the radio. The faster it changes the worse the timing error. That is what the external high precision oscillator fixes. With a precision oscillator the pos number only changes very slowly, maybe one or two over a three minute transmission. BER will rise slightly around pos changes because the sampling point of the data is not in an ideal position at these times. A steady sample position gives more consistent decodes.

The centre and threshold are the amplitude decision points used by the decoder when deciding the symbol values of an incoming transmission. They are calculated automatically from the max and min values of the received signal. Altering the receive level pot will change these. I don't think there is an optimum setting. My threshold tends to sit around 750. Higher values will make more use of the full range of the ADC so in theory they should provide better decoding.

A low RX level in MMDVM.ini brings low ADC overflow point regardless of the pot setting, so keep it high.

Colin G4EML