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A direct-sampling SDR doesn't require a mixer, which can simplify the design. Also, provided the receiver has sufficient dynamic range and processing power, a direct-sampling receiver can monitor all the bands at once. On the other hand, a direct-sampling SDR must have an ADC and DAC at a sample rate above twice the maximum frequency. So for an SDR that ...

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Everything works very well, but on some frequencies I hear loud AM broadcast stations. I think this is caused by harmonics from the VFO, but I am not sure. What you're possibly hearing is intermodulation distortions created by your receiver from the mixer and amplifier. A local AM broadcasting station has high radiated power, making the problem even worse. ...

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It might be harmonics of the oscillator, as you suppose, but it also might be that any mixer doesn't only produce the difference frequency of its two inputs ($|f_\text{RF}-f_\text{local oscillator}|$, here), but also higher-order intermodulation products (like $|2f_\text{RF}-f_\text{LO}|$ and $|f_\text{RF}-2f_\text{LO}|$). I think I've posted multiple ...

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On the one hand: just add the numbers. 50 dBm + 24 dB - 30 dB + 24 dB = 68 dBm. On the other hand: that's more power out than in! What that's telling you is that you will never have path loss as low as 30 dB and a pair of 24 dB gain antennas at the same time. For instance, say we're working at a wavelength of 2 meters. The Friis formula tells us that the ...

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Growing up in Europe and hanging on the SW dial, there were lots of stations received in cities without even any special antenna gear. At a maximum a totally non-tuned wire thrown anywhere along an inner wall was all that was had. Lots of stuff was received even so. But that was Europe, Europe is crowded and small, and the stations were perhaps less than 500 ...

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