UHF Spectrum Update
Now that most of the dust has settled around the fate of the 700 MHz band, please keep these points in mind:
- 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.
Based on the latest FCC Report and Order, dated September 23, 2010, there are a number of important points relevant to wireless microphone users in the US.
- New, mobile “Super WiFi” devices will be allowed to share the broadcast RF spectrum (470 - 698 MHz) with DTV broadcasts and wireless microphones. The “white spaces” between TV broadcasts offer a lot of spectrum for these devices and is therefore very valuable to broadband service providers. For one thing, this range of frequencies provides good propagation characteristics with low power and practical antenna sizes.
- These broadband devices will be available both as personal/portable devices(100mW maximum power), 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.
- 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.
- The next major part of the FCC’s report & order is that there will be two TV channels reserved for wireless microphone and IEM use. However, these two channels will 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 it will likely be TV35 (596-602) and 38 (614-620) that will be reserved in this metro area for wireless microphone use. In another city it may be channels 38 and 39. Until these reserved channels are set by the FCC, we cannot know exactly which channels they will be in a given metro area. Ultimately, the new FCC mandated central database will be available to the public for lookup, so end users could know in advance which channels are available to them. This chart shows where the reserved channels are for 13 major markets.
- Based on this, the Lectrosonics blocks 23 (588.800 to 614.300 MHz) and 24 (614.400 to 639.900) will likely be popular blocks in many metro areas.
- Additionally, according to the new rules, fixed (4W) TVBD devices 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 TVBD devices. (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.).
- In most areas therefore, it is estimated that there will at least 40MHz of clear spectrum for wireless microphone use. This would support the use of at least 16, and perhaps as many as 32 or more channels of wireless microphones which can be successfully coordinated and operated simultaneously to a high degree of performance.
- As for the “unprotected” portions of the spectrum, please keep in mind that due to the nature of the signals from the new broadband “Super WiFi” devices (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.
- However, if 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.
- The FCC has also added the possibility of obtaining a temporary license in cases where users may need more channels 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.
- If you are already a Licensed Part 74 user, the same restrictions apply although registering in the database does not require a 30 day advance notice. As long as you register a few days in advance (in order that enough time has elapsed for the information to propagate to the database and hence be accessible to the new broadband devices).
- Finally, we will need to see how things turn out once these devices actually enter the market. This is likely to be many months from now, i.e., no sooner than mid-2011. The devices themselves must be manufactured and FCC certified and then distributed. The database must be in place and working. We will update this page at that time since we will know more about the realities of the situation.
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.