From 357451f6398749d20c6d458e36b2022fcd4131de Mon Sep 17 00:00:00 2001 From: Joris van Rantwijk Date: Sun, 5 Jan 2014 21:56:06 +0100 Subject: [PATCH] More notes about gain and filters. --- NOTES.txt | 30 ++++++++++++++++++++++++++++++ TODO.txt | 11 ++++++----- 2 files changed, 36 insertions(+), 5 deletions(-) diff --git a/NOTES.txt b/NOTES.txt index 78eeef5..c69ba7d 100644 --- a/NOTES.txt +++ b/NOTES.txt @@ -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) + diff --git a/TODO.txt b/TODO.txt index e3af8f5..800ef25 100644 --- a/TODO.txt +++ b/TODO.txt @@ -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