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Hello can a device emit unintentional RF emissions when there is no power supplied to the RF embedded device such as a wireless router ?

[UPDATE 1] YES when there is absolute NO power whatsoever supplied to the device. That includes AC,DC. battery and so on.....

[UPDATE 2] My apologies everyone but the questions refers to RF enable devices such as cell phones, wireless routers, cordless phones and any other RF device that has an embedded transmitter or transceiver**

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  • \$\begingroup\$ Yes it can (if you mean, no DC power) \$\endgroup\$
    – user16324
    Apr 11, 2016 at 13:58
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    \$\begingroup\$ So you're asking, can a device emit power when no power source is connected to it. Assuming there is no other power source (a battery or it receives power wirelessly or any other power source) then my answer would be no as there is no power to keep the emission going. \$\endgroup\$
    – Bimpelrekkie
    Apr 11, 2016 at 14:04
  • \$\begingroup\$ Physics, energy can't be created or destroyed. You can't create EM waves (RF) without an energy source (AC mains) or other EM waves \$\endgroup\$
    – Voltage Spike ♦
    Apr 11, 2016 at 17:09
  • \$\begingroup\$ @Brian what if there is no power whatsoever such as AC, DC or battery DC and so ? Would the answer be the same as what the others have said which is no ? Thank you. \$\endgroup\$
    – VikkiM
    Apr 13, 2016 at 7:38
  • \$\begingroup\$ @FakeMoustache one question is unintentional RF emissions typically emitted by way of an antenna or by way of the integrated circuits ? \$\endgroup\$
    – VikkiM
    Apr 13, 2016 at 7:43

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RF emissions are radiated power. That power has to come from somewhere. Physics can be annoying like that.

So, no, a unpowered device can't emit RF power on its own. Note that "unpowered" includes not just no externally supplied power, but also no use of internal stored power, like from a battery.

Unpowered devices can receive RF power, then reflect it or re-radiate it in some different pattern. In that case, the input power is the received RF. You still can't emit RF power without some kind of power input.

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  • \$\begingroup\$ The re-radiation can be particularly problematic when a device connected to an antenna is linear when powered, but becomes highly non-linear (thanks to protection diodes) when unpowered... \$\endgroup\$
    – user16324
    Apr 11, 2016 at 17:36
  • \$\begingroup\$ @Brian thanks very much that was the answer I was looking for reradiation. Radiation that is emitted or reradiated due to incidental rf waves that collect on the antenna of the non transmitting rf embedded device. Brian is this what you mean by reradiation and the source of the reradiation ? Thanks to everyone. \$\endgroup\$
    – VikkiM
    May 13, 2016 at 10:08
  • \$\begingroup\$ Exactly. For a simple example, some security tags consist of an antenna and a diode. The antenna receives on one frequency. the diode generates a harmonic of that, which is coupled to the same antenna : the alarm detects the harmonic. NB there is not "zero power" here, there is power received from the antenna. \$\endgroup\$
    – user16324
    May 13, 2016 at 10:15

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