I have an SDR (RTL2832u) that connects to an antenna and can receive over the air just fine. I'm wondering if the signal of a home cable connection would be too strong to connect to the SDR input or is it safe?

Say for example my home cable modem transmit power is 35dBmv. Downstream power is showing around 10dbmv. Is this too much RF energy to feed into the SDR's antenna input?

EDIT: My capture card uses the e4000 Elonics tuner. datasheet.


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    \$\begingroup\$ Since you created the new SDR tag, can you also fill in the wiki summary, so that I don't have to look up what SDR means? Thank you. \$\endgroup\$ – Federico Russo Sep 19 '12 at 14:48
  • \$\begingroup\$ Yes please. What is SDR- I looked at the RTL28xxx but there is no mention of SDR? Do you just want to watch cable on your USB DVB? Yea go for it . I used to do it. \$\endgroup\$ – Piotr Kula Sep 19 '12 at 16:04
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    \$\begingroup\$ SDR is well know and established acronym for software-defined radio. For those that want to know more about this specific receiver, this article may be helpful. \$\endgroup\$ – AndrejaKo Sep 19 '12 at 16:07
  • \$\begingroup\$ I added wiki article (my first) but it's awaiting approval. \$\endgroup\$ – Brad Hein Sep 19 '12 at 17:25
  • \$\begingroup\$ Updated question with actual power readings (per cable modem diagnostics page) in dbmv \$\endgroup\$ – Brad Hein Sep 19 '12 at 17:30

35 dBmV means "35 decibels stronger than 1 mV", or about 10^(35/20) = 56 mV RMS. 56 mV is a pretty small signal, so it's unlikely to damage any input that wouldn't be completely destroyed by the ESD of casual handling.

There is still the possibility (though unlikely) that the input signal may be too strong for the receiver and would cause clipping. This may make it hard to separate a weak signal of interest from harmonics of a stronger signal. If that happens, you could try placing an attenuator between the RTL2832u's input and the cable.


No, the RTL2832u will not be damaged by the cable signal. After all, that's the application it was originally designed for! You'll probably have to reduce the gain settings in your SDR software to get useful results, though.

  • \$\begingroup\$ Actually it was designed with an aerial antenna in mind! \$\endgroup\$ – Brad Hein Feb 8 '17 at 13:27

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