Wireless Guide


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Wireless microphone systems are a key component in almost every broadcast, motion picture, theatrical and sound stage production, as well as corporate, religious and educational venues. The Wireless Guide offers readers an excellent foundation in the concepts of designing and operating a wireless microphone system.

This guide is intended to uncover some of the mysteries behind the operating principles of wireless systems and help the reader separate fact from fiction when selecting a wireless system for a particular application. Far too much propaganda has been published by various manufacturers, with boastful, and sometimes incredible claims about the quality of the equipment being offered. Armed with an understanding of the basic principles of wireless operation, it becomes possible to see through the maze and make intelligent choices.

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FCC & Spectrum Updates

Broadcast Television Spectrum Incentive Auction NPRM

Although it has already been several years since the 700 MHz band was made unavailable for use by wireless microphones in the US, please keep these points in mind:

  1. No wireless microphone or IEM users are allowed (since June 12, 2010) to operate in the range between 698 and 806 MHz in the US.
  2. For those customers who would like to convert their Lectrosonics block 27, 28 or 29 systems to lower blocks, it applies only to current products and to those products purchased new within approximately the last 7 years from an authorized dealer. Please contact our This email address is being protected from spambots. You need JavaScript enabled to view it. for an exact quote.

The National Broadband Plan, outlined in 2012, promises further changes to the spectrum within the next 10 years. Here are the details of HR3630 including the upcoming incentive auction plan, scheduled for mid-2015.

This, along with the previous Report and Order from the FCC in September, 2010, means you need to be aware of the following points:


  1. New, mobile "Super WiFi" devices are now allowed to share the broadcast RF spectrum (470 - 698 MHz) with TV broadcasts and wireless microphones. These "White Space Devices" or WSDs will be available both as personal/portable devices (40 mW to 100mW maximum power depending on proximity to TV broadcasting channels), as well as for fixed installation (4W maximum power). Personal/portable devices however will not be allowed to operate below TV 21, thus in many cities the spectrum between 470 – 511 MHz will be a relatively good place to operate wireless microphones. Lectrosonics blocks 470 (470.1-495.6) and 19 (486.4-511.9) are in this frequency band. Currently we have received very few (5 as of February, 2014) reports of interference from WSDs.
  2. That said, many major metro areas have public safety channels within this part of the spectrum. For instance, Los Angeles has TV 14 (470-476), 16 (482-488) and 20 (506-512) as public safety channels. When using blocks 470 and 19, it will be important to avoid frequencies that fall within the public safety channels if they may be used in your locality.
  3. Currently there are two TV channels reserved for wireless microphone and IEM use. However, these two channels vary by metro area based on what TV channels are already occupied. In general, they will be the 2 closest unoccupied channels above and below channel TV37 (608-614). (TV37 itself is reserved for radio astronomy). If a particular locality does not have at least 1 unoccupied channel both below and above channel 37, then there will be 2 channels on one side assigned. So, for example, in Los Angeles, TV 36 (602-608) is already occupied, so TV27 and TV30 are the reserved channels in the LA metro area for wireless microphone use. This chart shows where the reserved channels are for 13 major markets.
  4. Additionally, according to the new rules, fixed (4W) WSDs may not operate in a channel adjacent to a broadcast TV station, so that will afford an additional level of protection for wireless microphones, especially in large urban centers. For example, if there is a licensed TV station on channel 25, fixed devices would not be able to operate on channels 24, or 26 (the adjacent channels). Or in LA, where TV channels 28, 31, 34, and 36, are in operation, fixed TVBD's would not be able to operate at all between channels 27-39 leaving channels 29, 30, 32, 33, 35, and 38 clear of these high powered WSDs. (It gets rather complicated in detail, but it may be possible that personal portable devices could operate there in those channels, but only if they include a GPS and a means of consulting the protected channels database, as well as limiting their power to only 40mW.).
  5. As for the "unprotected" portions of the spectrum, please keep in mind that due to the nature of the signals from the new broadband WSDs (digital modulation spread over 6 MHz) and the amount of power allowed - 100 mW for portable devices (only 40mW if operating in a channel adjacent to an occupied TV channel), and 4 W for fixed devices - that these signals will often appear as low-level noise in the spectrum. In addition, TV bands devices must use transmit power control to operate with the minimum power necessary for reliable communications and will therefore often operate at power levels below 40 mW. In the vast majority of cases where your wireless microphones are close to your antennas/receivers (such as on a stage) these new broadband signals will probably not cause a lot of problems. If, however, you are routinely running your wireless mics out at the limits of their range, you may indeed have issues due to the new competing signals.
  6. For unlicensed users, the FCC has also added the possibility of obtaining a temporary protection in cases where users may need more frequencies than what they can successfully coordinate within the protected channels. To do so, users must state that they have exhausted the protected and exclusion zone channels by operating at least 6 – 8 wireless mics in each available TV channel. Such licenses will need to be requested 30 days in advance of an event where the wireless mics will be used. Once this request is granted, the requested channels will be entered into a central database so that all TV Band devices will know to avoid these channels. Spectrum Bridge and Keybridge are services offering access to a database for white space protection.
  7. If you are already a Licensed Part 74 user, the same restrictions apply although registering in the database only requires a 24 hour advance notice.


  1. Based on the new legislation in HR3630, Lectrosonics, along with representatives from other manufacturers, content creators (ESPN, Disney, NBC) and top level frequency coordinators met with several parties within the FCC in February, 2014 to discuss the upcoming issues. Here is what we learned:
  2. It is possible that within 3-4 years following a successful spectrum auction (now planned for mid-2015) much of the 600 MHz band (blocks 24, 25 & 26) will be re-allocated and thus unavailable for our use. However, our view is that, realistically, we have 5-8 years before we are blocked from this band, based on the complication of the auction process and the massive pushback coming from content creators.
  3. Along with much of the 600 MHz band on the auction block, any TV broadcasters now located there will similarly have to vacate and "re-pack" down in the lower bands. This means that the remaining available spectrum will become even more congested than it is today. What this means to you is that good setup, good, solid equipment and proper planning will be essential for success.
  4. Another topic of discussion during the meetings with the FCC was the group's request for compensation for users who purchased new equipment following the 700 MHz auctions, and may have to again abandon this equipment within its service life. We are not sure how this will play out although you can imagine that the FCC was not warm to this idea.
  5. Finally, the group also asked for expansion of license eligibility to include other professional applications such as (ironically) government facilities, theater, churches, touring groups, etc. In other countries (UK, Canada, for instance) this categories of users are eligible for licenses.
  6. Meanwhile, we are researching potential alternative frequency bands for development of new product lines. Unfortunately, all practical frequency bands (up to 10 GHz) are occupied and thus we are looking at shared use. Until we have a clear path from the FCC on potential access to these new bands, we can't yet make a heavy investment.
  7. What can YOU do? First, if you have not already done so, register for a Part 74 license as soon as possible. With this, you will have additional protection and convenience via the White Space databases. You will also have a voice with the FCC (they aren't nearly as interested in the opinions of unlicensed users). Also, please let your elected federal officials know how important this issue is. Remember, content distribution (WSDs, LTE, etc.) requires content creation. That's you and your clients.

Lectrosonics is very concerned about these issues, and we hope to do everything possible to make you aware of what is happening and help you with the transition. If you have any questions, please don't hesitate to contact us.