joris
/
SoftFM
1
0
Fork 0
Code Pull Requests Activity

More notes about gain and filters.

This commit is contained in:
Joris van Rantwijk 2014-01-05 21:56:06 +01:00
parent 32dcfdd57f
commit 357451f639
2 changed files with 36 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
NOTES.txt
View File

@ -15,3 +15,33 @@ Casual test of ADC errors:
* I/Q gain mismatch in order of 4%
* I/Q phase mismatch in order of 1% of sample interval
With tuner in auto-gain mode, device autonomously switches between gain
settings during a run. The tuner gain seems to switch between ~ 24 dB
and ~ 34 dB without intermediate steps.
With RTL in AGC mode, the level of the digital sample stream is normalized
to -6 dBFS. Unknown whether this is an analog or digital gain stage.
Unknown whether AGC mode is coupled to Elonics IF gain or purely
a digital thing in the RTL chip.
Does this improve SNR or not?
Default settings in librtlsdr:
Elonics LNA gain: when auto tuner gain: autonomous control with slow update
otherwise gain as configured via rtlsdr_set_tuner_gain
Elonics mixer gain: autonomous control disabled,
gain depending on rtlsdr_set_tuner_gain
Elonics IF linearity: optimize sensitivity (default), auto switch disabled
Elonics IF gain: +6, +0, +0, +0, +9, +9 (non-standard mode)
Elonics IF filters: matched to sample rate (note this may not be optimal)
RTL AGC mode off
Local radio stations:
radio2 92600000 (good)
radio3 96800000 (good)
radio4 94300000 (bad)
qmusic 100700000 (medium)
radio538 102100000 (medium)
radio10 103800000 (bad)
radio west 89300000 (medium)

11
TODO.txt
View File

@ -1,12 +1,13 @@
* (experiment) measure raw signal for radio3, radio4 for ~ 1 minute
* different gain settings
* with/without RTL AGC mode
* with several IF gain settings
* confirm theories about effect of gain, IF gain, AGC
* (experiment) measure raw signal with several IF gain settings
with/without AGC mode
* figure out whether AGC mode is coupled to the Elonics IF gain settings
or purely an RTL-internal thing
* look for effect of gain on baseband SNR
* look for effect of ADC calibration on baseband SNR
* look for effect of IF bandwidth on baseband SNR
* (experiment) try if RTL AGC mode improves FM decoding
* (experiment) try if RTL2832 FIR filter can be optimized
* (feature) support 'M' 'k' suffixes for sample rates and tuning frequency
* (feature) implement off-line FM decoder in Python for experimentation