<story><title>iPhone audio detectable with AM radio</title><url>https://twitter.com/doctorcube/status/1300953606221422594</url></story><parent_chain></parent_chain><comment><author>commonjcb</author><text>It&amp;#x27;s probably by design, iPhones support magnetic-induction hearing aids, see here:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;support.apple.com&amp;#x2F;en-us&amp;#x2F;HT202186&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;support.apple.com&amp;#x2F;en-us&amp;#x2F;HT202186&lt;/a&gt;&lt;p&gt;The are 2 standards, the old &amp;quot;telecoil&amp;quot; (direct) and the new FM loop, both operating at low frequencies...&lt;p&gt;Both work at very short ranges (inverse cube of the distance)</text></comment>
<story><title>iPhone audio detectable with AM radio</title><url>https://twitter.com/doctorcube/status/1300953606221422594</url></story><parent_chain></parent_chain><comment><author>IndrekR</author><text>Most likely not an FCC (EMC) issue. This sounds like direct inductive coupling from speaker D class amplifier output (or power, which would be worse, but not likely) circuit at &amp;lt;100 kHz. Below 30 MHz only conducted emissions are measured (common mode emission via cable, say, forming a large antenna together with the power grid). The emitting component may be the speaker or (unshielded) output filter (for EMC compliance!) of the amplifier.&lt;p&gt;Why it is not an issue, is that magnetic field decays really rapidly, (inversely proportional to the cube of the distance [1]) and thus is not a general concern. In fact some &amp;quot;secure by physics&amp;quot; nearby communication methods like RuBee [2] relay on this.&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Near_and_far_field&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Near_and_far_field&lt;/a&gt;&lt;p&gt;[2] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;RuBee&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;RuBee&lt;/a&gt;</text></comment>