2014-01-05 16:33:05 +01:00
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This file contains random notitions
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-----------------------------------
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2014-01-05 22:01:22 +01:00
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Sample rates between 300001 Hz and 900000 Hz (inclusive) are not supported.
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2014-01-05 16:33:05 +01:00
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They cause an invalid configuration of the RTL chip.
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rsamp_ratio = 28.8 MHz * 2**22 / sample_rate
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If bit 27 and bit 28 of rsamp_ratio are different, the RTL chip malfunctions.
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The RTL chip has a configurable 32-tap FIR filter.
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RTL-SDR currently configures it for cutoff at 1.2 MHz (2.4 MS/s).
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Casual test of ADC errors:
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* DC offset in order of 1 code step
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* I/Q gain mismatch in order of 4%
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* I/Q phase mismatch in order of 1% of sample interval
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2014-01-05 21:56:06 +01:00
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With tuner in auto-gain mode, device autonomously switches between gain
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2014-01-09 21:18:44 +01:00
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settings during a run. The LNA gain seems to switch between ~ 24 dB
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2014-01-05 21:56:06 +01:00
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and ~ 34 dB without intermediate steps.
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With RTL in AGC mode, the level of the digital sample stream is normalized
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2014-01-09 21:18:44 +01:00
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to -6 dB FS.
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Unknown whether this is an analog or digital gain stage.
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2014-01-05 21:56:06 +01:00
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Does this improve SNR or not?
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2014-01-09 21:18:44 +01:00
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At first I suspected that AGC mode may be a cooperation between the RTL and
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the Elonics tuner. I thought that the RTL would monitor the level and send
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digital control signals to the Elonics to dynamically change the tuner IF gain.
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However that is in fact NOT what happens. (Manually changing IF gain in AGC
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mode causes a brief level spike, while manually rewriting the same IF gain in
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AGC mode does not have any effect).
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It seems more likely that AGC is a digital gain in the downsampling filter.
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2014-01-05 21:56:06 +01:00
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Default settings in librtlsdr:
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Elonics LNA gain: when auto tuner gain: autonomous control with slow update
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otherwise gain as configured via rtlsdr_set_tuner_gain
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Elonics mixer gain: autonomous control disabled,
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gain depending on rtlsdr_set_tuner_gain
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Elonics IF linearity: optimize sensitivity (default), auto switch disabled
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Elonics IF gain: +6, +0, +0, +0, +9, +9 (non-standard mode)
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Elonics IF filters: matched to sample rate (note this may not be optimal)
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RTL AGC mode off
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Local radio stations:
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radio2 92600000 (good)
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radio3 96800000 (good)
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radio4 94300000 (bad)
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qmusic 100700000 (medium)
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radio538 102100000 (medium)
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radio10 103800000 (bad)
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radio west 89300000 (medium)
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