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Topic: Dumb Dirt Cheeep Wireless Environment Sensor (Read 15402 times) previous topic - next topic


Jan 04, 2011, 05:21 pm Last Edit: Jan 04, 2011, 05:28 pm by AltairLabs Reason: 1
gardner, Grumpy_Mike,

Youre partly right, except the sparkfun wireless ARE legal.  The freqs 315 and 433 are authorized for use subject to restrictions.  They are Govt frequencies.  The key to understanding legality of these is the terms "PRIMARY", "SECONDARY", "CO-SECONDARY", "LICENSED", "UNLICENSED" and "HARMFUL INTERFERENCE" as defined in CFR 47, which is the telecommunications law of the USA.

315 is military UHF for aviation, the sparkfun TX (actually IIRC made by HolyStone) are authorized as UNLICENSED CO_SECONDARY devices with relaxed technical specifications and low power.  

CO-SECONDARY means if a primary user come to you and says knock it off you must knock it off.  Any PRIMARY user may complain at any time that you are causing HARMFUL INTERFERENCE, and their complaint instantly has force of law, and without any further notice or legal action on their part any further operation on your part at that location is now illegal.  

UNLICENSED means you kowtow to LICENSED CO-SECONDARY users also.

433 is military radar, similar situation.  Ham radio are LICENSED CO-SECONDARY and may legally run hundreds of watts, and can legally shut you down with a single complaint.  But in turn several UHF repeaters in ham band were shut down, re located, etc. due to proximity and HARMFUL INTERFERENCE with nearby PAVE PAWS radar sites who are PRIMARY.  

Its a food chain, and these UNLICENSED devices are at the bottom, but are *absolutely legal* under the restrictions given.  Otherwise FCC could come down on SparkFun for selling them.  Obviously its illegal to use with a power amplifier, not so obviously it also may be illegal to use high gain antennas.  

Globally, other nations in ITU region 2 have similar rules, the other two ITU regions may vary somewhat more.  From the ITU the US Executive Office inherits frequency spectrum by international treaty, which is delegated to Commerce Dept and down to NTIA.  From there the NTIA divvies it up and coordinates between FCC for civilians and DoD for military.  We little civilians get ours from FCC.  

See the NTIA chart of US Allocations at


Although my SparkFun modules have not yet arrived they should come with a legal notice
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions:
1. This device may not cause harmful interference.
2. This device must accept any interference received, including interference that may cause undesired operation.

I forgat to mention the second condition of being UNLICENSED CO-SECONDARY (bottom of the food chain) is that you may not complain about anyone who outranks you, no matter how much HARMFUL INTERFERENCE they cause to *YOU*.   ;D


Hi Guys, Ive only just found this topic, and its a subject close to my heart, so i joined the forum. Ive recently purchased an Arduino clone, the Seeeduino, so it will take a little time for me to get upto speed on the software side of things, hopefully i will soon be able to offer my contributions in the near future, so in the meantime excuse any dumb questions guys.

John UK


Welcome, John from UK, the development is proceeding under the name.
Dirt Cheap Dumb Wireless  =  DCDW
on a new Arduino Forum thread
and new web page
youre in plenty time to join in

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