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I am using SDRsharp to monitor air band with an RTL-SDR dongle. Sometimes I receive ATC voice clearly but at times it's distorted,

I am using RTL AGC gain of 29dB with no tuner gain. My filter bandwidth is 10 KHz but with 8-12Khz the results are identical. My antenna is a dipole placed outdoors.

What might cause reception to be distorted sometimes?

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An RTL-SDR is susceptible to overload from strong signals, such as from an AM broadcast station, from another aircraft flying overhead, or other nearby transmitters or sources of RFI.

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  • $\begingroup$ SDRSharp has the option to use RTL AGC and Tuner AGC besides setting RF gain. Does it mean that these AGCs are useless? $\endgroup$
    – user3696623
    Oct 5, 2022 at 18:16
  • $\begingroup$ Those AGCs were designed for DVB channel characteristics and modulation, not airband AM. And an AGC doesn't help much, if at all, if the overload greatly exceeds the dynamic range of the ADC. $\endgroup$
    – hotpaw2
    Oct 5, 2022 at 21:16
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    $\begingroup$ @user3696623 they're not useless, but they're not magic either. If a strong adjacent signal makes the AGC crank the gain down so that your desired signal is now lost in the quantization noise, well, what are you going to do about that? If intermod in the front-end covers up your desired signal with noise, how is AGC going to help? There are receivers with higher dynamic range, better linearity, and better filtering, if you want to get one of those. $\endgroup$
    – hobbs - KC2G
    Oct 6, 2022 at 4:45

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