RTL SDR device notes

Problems with Elonics E4000 tuners

RTL-SDR devices come in many sizes and shapes. One thing that will vary is the type of tuner chip that has been chosen by the manufacturer. As far as we are aware, all of them work, including the E4000 tuner. There has been many reports of issues with devices containing E4000 tuners though since they do not initially work due to the value "rf_gain": 30 that is contained in the default configuration. The E4000 tuners do not support this value, so the simple solution for these issues is to change this to a supported value (the next possible values are 29 and 34).

One other very common complaint with the E4000 tuners is that they show a very prominent DC offset, which shows as a very strong "line" going right down the middle of the waterfall, sometimes even flanking out to the sides. This cannot be fixed by OpenWebRX since it is contained in the IQ data that is sent by the device, or in other words: What you see is what OpenWebRX receives from the hardware. There is algorithms to compensate for this issue, they are however unable to recover any signals that have been compromised. OpenWebRX does not currently implement any such algorithm.

Sample configuration

This config shows some more advanced use of an RTL-SDR device, including the direct_sampling mode which allows to tune to shortwave frequencies. Please note that direct sampling is not available on al RTL-SDR devices.

sdrs = {
    "rtlsdr": {
        "name": "RTL-SDR",
        "type": "rtl_sdr",
        "ppm": 0,
        "direct_sampling": 0,
        "profiles": {
            "NOAA": {
                "name": "NOAA Weather",
                "center_freq": 162475000,
                "rf_gain": 30,
                "samp_rate": 2000000,
                "start_freq": 162475000,
                "start_mod": "nfm",
            },
            "2m": {
                "name": "2m Packet",
                "center_freq": 144390000,
                "rf_gain": 30,
                "samp_rate": 2000000,
                "start_freq": 144390000,
                "start_mod": "nfm",
            },
            "70cm": {
                "name": "70cm 440",
                "center_freq": 438800000,
                "rf_gain": 30,
                "samp_rate": 2000000,
                "start_freq": 439275000,
                "start_mod": "nfm",
            },
            "FM1": {
                "name": "FM1",
                "center_freq": 9000000,
                "rf_gain": 10,
                "samp_rate": 2000000,
                "start_freq": 9000000,
                "start_mod": "wfm",
            },
            "20m": {
                "name": "20m",
                "center_freq": 14150000,
                "rf_gain": 10,
                "samp_rate": 2000000,
                "start_freq": 14070000,
                "start_mod": "usb",
                "direct_sampling": 2,
            },
            "30m": {
                "name": "30m",
                "center_freq": 10125000,
                "rf_gain": 10,
                "samp_rate": 2000000,
                "start_freq": 10142000,
                "start_mod": "usb",
                "direct_sampling": 2,
            },
            "40m": {
                "name": "40m",
                "center_freq": 7100000,
                "rf_gain": 10,
                "samp_rate": 2000000,
                "start_freq": 7070000,
                "start_mod": "usb",
                "direct_sampling": 2,
            },
        },
    },
}