diff --git a/NOTES.txt b/NOTES.txt index 30ad49b..893ec77 100644 --- a/NOTES.txt +++ b/NOTES.txt @@ -88,6 +88,10 @@ Strong stations benefit from a wider IF filter to reduce harmonics. Effect of settings on baseband SNR ---------------------------------- +Note: all measurements 10 second duration +Note: all measurements have LO frequency set to station + 250 kHz + + STATION SRATE LNA IF GAIN AGC SOFT BW IF LEVEL GUARD/PILOT radio3 1 MS/s 24 dB default off 150 kHz 0.19 -62.6 dB/Hz @@ -107,15 +111,57 @@ radio4 2 MS/s 34 dB default off 150 kHz 0.10 -42.4 dB/Hz radio4 2 MS/s 34 dB default off 80 kHz -48.2 dB/Hz radio4 2 MS/s 34 dB default off 150 kHz adccal -42.4 dB/Hz -Note: all measurements 10 second duration -Note: all measurements have LO frequency set to station + 250 kHz - Conclusion: Sample rate (1 MS/s to 2 MS/s) has little effect on quality. Conclusion: LNA gain has little effect on quality. Conclusion: Narrow IF filter improves quality of weak station. Conclusion: ADC gain/offset calibration has no effect on quality. +STATION SRATE LNA IF GAIN AGC SOFT BW IF LEVEL GUARD/PILOT + +radio3 2 MS/s 34 dB 9,0,0,0,9,9 off 80 kHz 0.38 -63.2 dB/Hz +radio3 2 MS/s 34 dB 0,0,0,0,3,3 off 80 kHz 0.03 -61.5 dB/Hz +radio3 2 MS/s 34 dB 0,0,0,0,3,9 off 80 kHz 0.07 -61.5 dB/Hz +radio3 2 MS/s 34 dB 0,0,0,0,3,15 off 80 kHz 0.11 -60.5 dB/Hz +radio3 2 MS/s 34 dB 0,0,0,0,9,15 off 80 kHz 0.22 -61.0 dB/Hz +radio3 2 MS/s 34 dB 0,0,0,0,15,15 off 80 kHz 0.36 -61.4 dB/Hz +radio3 2 MS/s 34 dB 0,0,6,0,15,15 off 80 kHz 0.66 CLIP -63.5 dB/Hz +radio3 2 MS/s 34 dB 0,6,0,0,3,3 off 80 kHz 0.07 -62.9 dB/Hz +radio3 2 MS/s 34 dB 9,3,0,0,3,3 off 80 kHz 0.14 -63.9 dB/Hz +radio3 2 MS/s 34 dB 9,9,0,0,3,3 off 80 kHz 0.26 -64.2 dB/Hz +radio3 2 MS/s 34 dB 9,9,3,2,3,3 off 80 kHz 0.45 -64.1 dB/Hz +radio3 2 MS/s 34 dB 9,9,6,0,3,3 off 80 kHz 0.49 -63.7 dB/Hz +radio3 2 MS/s 34 dB 9,9,9,0,6,3 off 80 kHz 0.77 CLIP -61.2 dB/Hz + +radio4 2 MS/s 34 dB 9,0,0,0,9,9 off 80 kHz 0.09 -41.5 dB/Hz +radio4 2 MS/s 34 dB 0,0,0,0,3,3 off 80 kHz 0.01 -36.7 dB/Hz +radio4 2 MS/s 34 dB 0,0,0,0,3,9 off 80 kHz 0.02 -39.9 dB/Hz +radio4 2 MS/s 34 dB 0,0,0,0,3,15 off 80 kHz 0.03 -40.4 dB/Hz +radio4 2 MS/s 34 dB 0,0,0,0,9,15 off 80 kHz 0.06 -39.9 dB/Hz +radio4 2 MS/s 34 dB 0,0,0,0,15,15 off 80 kHz 0.09 -40.9 dB/Hz +radio4 2 MS/s 34 dB 0,0,6,0,15,15 off 80 kHz 0.17 -38.4 dB/Hz +radio4 2 MS/s 34 dB 0,6,0,0,3,3 off 80 kHz 0.02 -36.9 dB/Hz +radio4 2 MS/s 34 dB 9,3,0,0,3,3 off 80 kHz 0.03 -37.5 dB/Hz +radio4 2 MS/s 34 dB 9,9,0,0,3,3 off 80 kHz 0.07 -39.4 dB/Hz +radio4 2 MS/s 34 dB 9,9,3,2,3,3 off 80 kHz 0.11 -38.5 dB/Hz +radio4 2 MS/s 34 dB 9,9,6,0,3,3 off 80 kHz 0.12 -38.0 dB/Hz +radio4 2 MS/s 34 dB 9,9,9,0,6,3 off 80 kHz 0.22 -37.5 dB/Hz + +Conclusion: IF gain has little effect on quality, although very low gain + has an adverse effect. Librtlsdr defaults look good. + + +STATION SRATE LNA IF GAIN AGC SOFT BW IF LEVEL GUARD/PILOT + +radio3 2 MS/s 34 dB default off 80 kHz 0.36 -62.1 dB/Hz +radio3 2 MS/s 34 dB default ON 80 kHz 0.36 -61.6 dB/Hz + +radio4 2 MS/s 34 dB default off 80 kHz 0.11 -38.5 dB/Hz +radio4 2 MS/s 34 dB default ON 80 kHz 0.36 CLIP -38.0 dB/Hz + +Conclusion: AGC mode has little effect on quality. + + Local radio stations -------------------- diff --git a/TODO.txt b/TODO.txt index d9e0683..9ff5f34 100644 --- a/TODO.txt +++ b/TODO.txt @@ -1,8 +1,5 @@ * (experiment) consider reducing IF filter bandwidth to ~ 80 kHz * (experiment) consider downsampling IF signal before FM detection -* (experiment) measure effect of IF gain on baseband SNR -* (experiment) measure effect of IF gain linearity on baseband SNR -* (experiment) measure effect of RTL AGC mode on baseband SNR * (experiment) try if RTL AGC mode improves FM decoding * (feature) support 'M' 'k' suffixes for sample rates and tuning frequency