#1 2015-11-30 14:47:50

DB1NTO
Member
Registered: 2014-12-01
Posts: 52

How important is the ADC BIAS resistor precision for decoding?

Hi Mark,

how important is the BIAS voltage accodring to decoding performance?

Correct BIAS and AREF give us a ADC value of 512 (half of 1024).
What is, if the ADC value is 500 instead 512 with no audio on input due to resistor tolerances?

I have made some tests and think that makes a noticeable difference. Can this be true?
Especially on LOW audio sources! Maybe the audio is then complete below the 0 line?
If its so. We should think about to implement a ADC "calibration procedure" to learn correct center of BIAS voltage.
If your code meassures the zero crossings for demodulate, this can be a good idea to improve decoding of weak signals!

Thank you for your reply.

Taner

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#2 2015-12-01 11:19:29

LZ1PPL
Member
Registered: 2014-12-22
Posts: 13

Re: How important is the ADC BIAS resistor precision for decoding?

Hi Taner,

I have made one experiment. When i use lm1117 and an 5% resistors i got like 10% less decoded packet then when i use precision voltage regulator like TC1014 and 1% resistors. So i think it make a big difference.

73 LZ1PPL
Plamen

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#3 2015-12-14 19:06:57

markqvist
Administrator
Registered: 2014-12-01
Posts: 112

Re: How important is the ADC BIAS resistor precision for decoding?

As LZ1PPL summed up, it is very important smile A bad/usntable reference voltage will basically ruin your decoding.

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