[teknoids] "white spaces" rules may create wireless microphone problems for law schools

Overdorf, Ryan ryan.overdorf at utoledo.edu
Thu Sep 30 16:41:28 EDT 2010

Last week the FCC released its White Spaces Second Memorandum Opinion and Order (http://www.fcc.gov/Daily_Releases/Daily_Business/2010/db0924/FCC-10-174A1.pdf <http://www.fcc.gov/Daily_Releases/Daily_Business/2010/db0924/FCC-10-174A1.pdf> ) regulating Television Band Devices (TVBDs). Law schools are likely to benefit from these "super WiFi" devices.


Alas, wireless microphones at law schools and similar institutions will be protected from interference by TVBDs only if operating on certain TV channels.  TVBDs are prohibited from operating on the first vacant TV channel above and below channel 37. The FCC refers to these as "reserved" channels for wireless microphones (but the first vacant channel in a given market might change over time due to TV station changes). Vacant channels from 14-21 will also be reserved for wireless microphones in most markets (but with a host of caveats that would unnecessarily complicate this summary).


You can find a list of TV channel frequencies at 47 CFR § 73. 603(a) (http://edocket.access.gpo.gov/cfr_2009/octqtr/pdf/47cfr73.603.pdf) if you are not sure which channels your microphones operate in.  The number of microphones that can be protected in a reserved channel depends on the manufacturer and model of wireless microphones. You can consult your manufacturer's manual for a chart or use the FCC list to create your own chart.


The vendors have been selling replacement microphone systems to the church and educational market that operate on channels not reserved because the vendors guessed wrong about the final rules.  Too many technical details are still unknown to quantify the interference risk. However, if your institution owns wireless microphones operating on unreserved channels, there is a distinct possibility that they will not continue to be reliably interference free.


In my own case, the College of Law administration gave me permission to wait until I saw the final rules before purchasing new microphones to replace the ones the FCC prohibited (even though it meant a reduced number of microphones for a few months).  The use of wireless microphones is important enough to my institution that the administration was willing to accept the risk of the new microphones being prohibited when the FCC reallocates more of the TV spectrum in 2015. 


TVBDs may not reach the market for another year or more. If your institution has not recently purchased new microphones but plans to in spite of the obsolescence risk, you will be able to select systems that operate on reserved channels in your area.  If your institution cannot afford to purchase new microphones (e.g., if you just purchased new microphones operating on unreserved channels to comply with the 700 MHz ban), there may be ways to mitigate the interference risk.


You may be able to increase the microphone squelch sufficiently to suppress a TVBD signal. Unfortunately, no one will know whether this works until the first time someone walks in with a TVBD. You can also institute the airline rule. Unfortunately, no one yet knows how much of a "quiet zone" is needed.


Please feel free to e-mail me if you have questions or think you might have wireless microphone issues. I can give you or help you find as much detail as you need.



Ryan S. Overdorf

Senior Electronic/Media Services Librarian

LaValley Law Library 

University of Toledo College of Law

(419) 530-2759

Ryan.Overdorf at utoledo.edu <mailto:Ryan.Overdorf at utoledo.edu> 


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