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FCC Part 15.249

FCC Part 15.249

FCC Part 15.249

I would appreciate helping me with interpretation of the FCC Part 15.249 regulations.
Section 249 allows for low power (EM field less than 50 mV/m) devices to operate with a fixed carrier - no spread spectrum.   That section points specifically to “fixed” entities.
So, the question is …
Is a hand-held unit, with a capability to transmit a signal, in the “fixed” device category, Section 249 talks about?  What if I move my sniffer arround?  What if I mount my sniffer onto a truck, and I interrogate slave devices while I drive?  I need to transmit short radio packets to do that.
I don’t see any reference, in the section 249, preventing moving my transmitting entity to different locations?
Is this the right way to interpret the section 15.249?
Would my sniffer need to comply with any other FCC regulations?


RE: FCC Part 15.249

15.249 Section A applies to all transmitters - portable devices like yours and fixed devices; this is where the 50 mV/m limit is defined.  Section B applies to fixed systems only.  

You'll also need to read through sub-part B (15.107 and 15.109 come to mind) to check for unintentional emissions.  

RE: FCC Part 15.249

Now that I look at it again the wording is very vague in 15.249.  Why don't you operate under 15.245 where you can have 500 mV/m (10x more)?  15.245 is where most cordless phones are  operating and they are very mobile.  

RE: FCC Part 15.249

Hi Zappedagain,
Operating below 50 mV/m allows fixed carrier (at a chosen frequency), with "old" FM-like modulation (FM, FSK, PSK, ..., also AM, OOK, ...). To generate 500 mV/m a spread spectrum is needed, complicating the transmit/receive circuit. The spread spectrum usually is FHSS or DSSS, with a number of modulation techniques allowed.  Spread spectrum needs extra time to lock and synchronize the receiver.
A simplified system (with a fixed carrier) can work below 50 mV/m within tens/hundreds feet of the range, but it is more sensitive to interference, and can be killed if a strong interfering harmonics (or a carrier) accidentally sits at the frequency of operation.

RE: FCC Part 15.249

Sorry, forget my reference to 15.245; I meant 15.231.  If you can tolerate a 10% duty cycle (10 mS packet every 100 mS) you can get the same power in 15.231 as 15.249 (see 15.231e and 15.35c).  15.231 allows the use of omnidirectional antennas.  

The FCC has set up mailboxes (oetinfo@fcc.gov, https://gullfoss2.fcc.gov/prod/oet/cf/kdb/forms/InquiryForm.cfm) where you can ask for clarification on issues like this.  

Check out http://www.fcc.gov/oet/faqs/ for more info.  

Good luck.  

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