rtlsdr ppm correction, how

janvgils commented 4 years ago

How can we correct the ppm value with soapyrtlsdr? The current SoapySDRUtil --probe="driver=rtlsdr" isn't showing a corr=value option anymore.

`SoapySDRUtil --probe="driver=rtlsdr" ######################################################

Soapy SDR -- the SDR abstraction library

######################################################

Probe device driver=rtlsdr Found Rafael Micro R820T tuner Found Rafael Micro R820T tuner

-- Device identification

driver=RTLSDR hardware=R820T origin=https://github.com/pothosware/SoapyRTLSDR rtl=0

-- Peripheral summary

Channels: 1 Rx, 0 Tx Timestamps: NO Other Settings:

Direct Sampling - RTL-SDR Direct Sampling Mode [key=direct_samp, default=0, type=string, options=(0, 1, 2)]
Offset Tune - RTL-SDR Offset Tuning Mode [key=offset_tune, default=false, type=bool]
I/Q Swap - RTL-SDR I/Q Swap Mode [key=iq_swap, default=false, type=bool]
Digital AGC - RTL-SDR digital AGC Mode [key=digital_agc, default=false, type=bool]

-- RX Channel 0

Full-duplex: YES Supports AGC: YES Stream formats: CS8, CS16, CF32 Native format: CS8 [full-scale=128] Stream args:

Buffer Size - Number of bytes per buffer, multiples of 512 only. [key=bufflen, units=bytes, default=262144, type=int]
Ring buffers - Number of buffers in the ring. [key=buffers, units=buffers, default=15, type=int]
Async buffers - Number of async usb buffers (advanced). [key=asyncBuffs, units=buffers, default=0, type=int] Antennas: RX Full gain range: [0, 49.6] dB TUNER gain range: [0, 49.6] dB Full freq range: [23.999, 1764] MHz RF freq range: [24, 1764] MHz CORR freq range: [-0.001, 0.001] MHz Sample rates: 0.25, 1.024, 1.536, 1.792, 1.92, 2.048, 2.16, 2.56, 2.88, 3.2 MSps`

kerel-fs commented 4 years ago

To answer a part of the question our-self: There are two possible ways to set the frequency correction via the provided SoapySDR APIs:

via Frequency API by SoapyRTLSDR::setFrequency with name="CORR":

const double corr_frequency = 49;  # in ppm
std::vector<SoapySDR::Kwargs> d_tune_args;
d_device->setFrequency(SOAPY_SDR_RX, channel, "CORR", corr_frequency, d_tune_args);

via Frontend corrections API by SoapyRTLSDR::setFrequencyCorrection

const double corr_frequency = 49;  # in ppm
d_device->setFrequencyCorrection(SOAPY_SDR_RX, channel, corr_frequency);

(Note that the underlying rtlsdr_set_freq_correction method supports integer values only (include/rtl-sdr.h#L155-L162) while both Soapy APIs accept doubles and type-casts them.)

The only question remaining: Which of those two possibilities is preferred / do you plan to deprecate one of the two APIs in the future?

cjcliffe commented 4 years ago

Looks like setFrequencyCorrection was added two years after the initial method of using "CORR" as a workaround was implemented.

Use setFrequencyCorrection and consider calling setFrequency with "CORR" to be deprecated -- I'll be updating my own application to use the new function as well so that it will work with all supported devices.

pothosware / SoapyRTLSDR