DD4WH June, 9th 2016
====================



./hardware/mchf_board.h:

    uchar       display_dbm;                    // display dbm or dbm/Hz or OFF
    uchar       s_meter;                        // defines S-Meter style/configuration


./drivers/ui/menu/ui_menu_internal.h:    
// Enumeration for menu.
enum
{
...
  MENU_DBM_CALIBRATE,
...
}

./drivers/ui/ui_configuration.h:
#define EEPROM_DBM_CALIBRATE                379

./drivers/audio/audio_driver.h:    
  float32_t dbm;
  float32_t dbmhz;

// S meter public
typedef struct SMeter
{
    ulong       skip;
    ulong       s_count;
    float       gain_calc;
    int         curr_max;
    float32_t dbm;
    float32_t dbmhz;

} SMeter;


extern __IO SMeter              sm;

./drivers/audio/audio_driver.c

void AudioDriver_Init(void)
{
...
    // Reset S meter public
    sm.skip             = 0;
    sm.s_count  = 0;
    sm.curr_max = 0;
    sm.gain_calc = 0;   // gain calculation used for S-meter
...
}


./drivers/ui/ui_driver.c

static void UiDriver_HandleSMeter()
{
...
            else if (ts.s_meter == DISPLAY_S_METER_DBM) // based on dBm calculation
            {
                sm.gain_calc = sm.dbm;
            }
...
            // find corresponding signal level
            for (
                    sm.s_count = 0;
                    (sm.gain_calc >= S_Meter_Cal_Ptr[sm.s_count]) && (sm.s_count < S_Meter_Cal_Size);
                    sm.s_count++)
            {
                // nothing to do here
            }
...
            // make sure that the S meter always reads something!
            UiDriver_UpdateTopMeterA((sm.s_count>0) ? sm.s_count : 1);
...
}

./drivers/ui/lcd/ui_spectrum.c
static void UiSpectrum_DisplayDbm()
{
...
  //Nur printout to LCD, do not care!
...
}

static void UiSpectrum_CalculateDBm()
{
...
        if( ts.txrx_mode == TRX_MODE_RX && ((ts.s_meter != DISPLAY_S_METER_STD) || (ts.display_dbm != DISPLAY_S_METER_STD )))
        {
            float32_t slope = 19.8; // 19.6; --> empirical values derived from measurements by DL8MBY, 2016/06/30, Thanks!

...
            float32_t bin_BW = (float32_t) (IQ_SAMPLE_RATE_F * 2.0 / buff_len);
            // width of a 256 tap FFT bin = 187.5Hz
            // we have to take into account the magnify mode
            // --> recalculation of bin_BW
            bin_BW = bin_BW / (1 << sd.magnify); // correct bin bandwidth is determined by the Zoom FFT display setting

            int buff_len_int = FFT_IQ_BUFF_LEN;

            //  determine posbin (where we receive at the moment) from ts.iq_freq_mode

            // frequency translation off, IF = 0 Hz OR
            // in all magnify cases (2x up to 32x) the posbin is in the centre of the spectrum display
...
}