<story><title>Turning the Raspberry Pi Into an FM Transmitter</title><url>http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter</url></story><parent_chain><item><author>jdietrich</author><text>&lt;i&gt;Emissions must be kept within the 88.0 to 108.0 MHz band&lt;/i&gt;&lt;p&gt;Without a spectrum analyser, you have absolutely no idea how much energy is being emitted on other frequencies. A crude unfiltered transmitter of this sort is probably emitting more spurious energy than on the intended frequency. Ignorance is no defence and it is the obligation of the operator to ensure that their transmission is compliant.&lt;p&gt;Lots of serious, life-or-death stuff depends on radio. The FM broadcast frequencies are directly adjacent to the VHF Airband, either side of 108MHz. The lowest part of the Airband is allocated to VOR and ILS navigation aids. Transmit a couple of watts on 107MHz and you&apos;re just going to interfere with broadcast radio; A couple of watts on 109MHz could take down a light aircraft. If you&apos;re going to experiment, you have a moral duty to get yourself an amateur license and ensure you have the skills and equipment to be a good neighbour.</text></item><item><author>bhousel</author><text>&lt;a href=&quot;http://en.wikipedia.org/wiki/Part_15_%28FCC_rules%29&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Part_15_%28FCC_rules%29&lt;/a&gt;&lt;p&gt;&lt;i&gt;Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.&lt;/i&gt;</text></item><item><author>meaty</author><text>I bet the FCC (or RCA in the UK) will love that :)&lt;p&gt;The amount of noise and harmonics that come off that sort of transmitter will be horrible. At least chuck a bandpass on the end of it.</text></item></parent_chain><comment><author>bigiain</author><text>While I agree with everything you say, this:&lt;p&gt;&quot;A couple of watts on 109MHz could take down a light aircraft.&quot;&lt;p&gt;is without doubt the sort of unnecessary hyperbolic statement that leads directly to the modern security-theatre over reaction. Sure, it might lead to navigation problems which combined with enough other co-incidental bad luck might lead to a crash, but the reductio ad absurdum statement &quot;$30 worth of widely available electronics could crash a Cessna&quot; would surely lead to an entirely justified call from Cessna&apos;s legal department if published prominently enough.&lt;p&gt;Yeah, fucking around with poorly controlled transmitters in the FM broadcast band isn&apos;t a great idea. but telling people &quot;you&apos;ll crash planes!&quot; is a sure-fire way to have the rest of your message&apos;s reliability questioned.&lt;p&gt;(And, for the record, I&apos;m going to try this out with my RaspberryPi and see if I can get some sort of handle on unexpected emissions using my FunCube software radio to listen above and below the tx frequency...)</text></comment>
<story><title>Turning the Raspberry Pi Into an FM Transmitter</title><url>http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter</url></story><parent_chain><item><author>jdietrich</author><text>&lt;i&gt;Emissions must be kept within the 88.0 to 108.0 MHz band&lt;/i&gt;&lt;p&gt;Without a spectrum analyser, you have absolutely no idea how much energy is being emitted on other frequencies. A crude unfiltered transmitter of this sort is probably emitting more spurious energy than on the intended frequency. Ignorance is no defence and it is the obligation of the operator to ensure that their transmission is compliant.&lt;p&gt;Lots of serious, life-or-death stuff depends on radio. The FM broadcast frequencies are directly adjacent to the VHF Airband, either side of 108MHz. The lowest part of the Airband is allocated to VOR and ILS navigation aids. Transmit a couple of watts on 107MHz and you&apos;re just going to interfere with broadcast radio; A couple of watts on 109MHz could take down a light aircraft. If you&apos;re going to experiment, you have a moral duty to get yourself an amateur license and ensure you have the skills and equipment to be a good neighbour.</text></item><item><author>bhousel</author><text>&lt;a href=&quot;http://en.wikipedia.org/wiki/Part_15_%28FCC_rules%29&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Part_15_%28FCC_rules%29&lt;/a&gt;&lt;p&gt;&lt;i&gt;Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.&lt;/i&gt;</text></item><item><author>meaty</author><text>I bet the FCC (or RCA in the UK) will love that :)&lt;p&gt;The amount of noise and harmonics that come off that sort of transmitter will be horrible. At least chuck a bandpass on the end of it.</text></item></parent_chain><comment><author>Nrsolis</author><text>Agree.&lt;p&gt;Amateur radio operators have dummy loads and SWR meters to make sure that the signal they are putting out isn&apos;t stomping on some other critical portion of the RF band.  Experimentation is a good thing, but this is the equivalent of someone being disturbingly careless experimenting with chemicals in their home &quot;lab.&quot;  The chance you could cause a serious problem with contamination for your neighbors is small but definitely non-zero.</text></comment>