Question often comes up, Answer: 27 feet / 9 meters with RTL-SDR dongles:
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For testing, I tried four separate RTL-SDR dongles in image above: rtl-sdr.com v3, Nooelec Mini 2, Nooelec E4000 SMArtee and regular Nooelec SMArt.
USB connector cable is crucial, as mentioned in a previous post detailing stuff I'm happy with, blue 5 feet / 1.5 m USB connector with ferrites were used. Tried several USB connectors over the years, these worked best, 27 feet / 9 m connectors totaled 5 dollars off eBay.
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Computers were a Lenovo and a ThinkPad, identical results, all computers provide 5V to USB devices, so host computer should not matter.
Nope at these extreme lengths, in fact, better with once section of USB cable as receiver is moved away from computer, didn't see any noise pickup from 5 feet /1.5 m to 27 feet / 9 meters.
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If distance between antenna and receiver is within these lengths, substitute coax with USB cables. Cheaper, and since signal received is immediately chewed into digital ones and zeros, there's no chance of electrical noise pickup by coax cable.
Doubtful? Check printscreens of various lengths, top image without any USB cable connection, then adding one section (5 feet / 1.5m) at a time.
Really, I can't see any changes between the second image from top (one section) and the last image on the bottom (5 sections).
For testing, I tried four separate RTL-SDR dongles in image above: rtl-sdr.com v3, Nooelec Mini 2, Nooelec E4000 SMArtee and regular Nooelec SMArt.
USB connector cable is crucial, as mentioned in a previous post detailing stuff I'm happy with, blue 5 feet / 1.5 m USB connector with ferrites were used. Tried several USB connectors over the years, these worked best, 27 feet / 9 m connectors totaled 5 dollars off eBay.
Computers were a Lenovo and a ThinkPad, identical results, all computers provide 5V to USB devices, so host computer should not matter.
Noise pickup
Nope at these extreme lengths, in fact, better with once section of USB cable as receiver is moved away from computer, didn't see any noise pickup from 5 feet /1.5 m to 27 feet / 9 meters.
Try not to use coax below 20 feet / 6 meter
If distance between antenna and receiver is within these lengths, substitute coax with USB cables. Cheaper, and since signal received is immediately chewed into digital ones and zeros, there's no chance of electrical noise pickup by coax cable.Doubtful? Check printscreens of various lengths, top image without any USB cable connection, then adding one section (5 feet / 1.5m) at a time.
Really, I can't see any changes between the second image from top (one section) and the last image on the bottom (5 sections).