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Experimented with IF gain and AGC mode; does not seem to help much.

This commit is contained in:
Joris van Rantwijk 2014-01-12 22:08:22 +01:00
parent 4619295d9a
commit ff985cd623
2 changed files with 49 additions and 6 deletions
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52
NOTES.txt
View File

@ -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
--------------------

3
TODO.txt
View File

@ -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