Wireless Microphone FAQ

[mbenonis]

I've decided to post a list of frequently asked questions relating to the RF side of wireless microphones, digital TV, the 700 MHz auctions, and related issues. It will be geared toward the United States, but I will try to research other countries' laws if it is requested.

The FAQ is very much a work in progress, and I will be updating it regularly. Please feel free to post additional questions, and I'll try to answer them and add them to this FAQ.

New May 20, 2008:
I've added the tutorial to my website, and to keep things simple (so I don't have to update both places every time I change it).

New September 8th, 2008:
Added information about 900 MHz wireless mics (DON'T BUY THEM!) and the NPRM for the 700 MHz spectrum.

New November 7, 2008:
Updated to reflect the reality of White Space Devices.

Last Updated: November 7, 2008.

http://benonis.net/?q=node/4

[Chris15]

Mike, I'm noticing an absence of mention to Wireless Workbench which from memory also will do the intermod calculations for one... As well as then updating the freqs on UHF-R or U series receivers upon direction. This after you connect an omni antenna and let it do a spectrum sweep...

[mbenonis]

Originally Posted by Chris15

Mike, I'm noticing an absence of mention to Wireless Workbench which from memory also will do the intermod calculations for one... As well as then updating the freqs on UHF-R or U series receivers upon direction. This after you connect an omni antenna and let it do a spectrum sweep...

I don't have any UHF-R systems, but I'll take a look into it.

[mbenonis]

I just updated the FAQ with a few new things.

[mbenonis]

Here's an article in Broadcast Engineering that summarizes the whole DTV/700 MHz spectrum issue very well:

http://broadcastengineering.com/audi...s_spaces_0307/

[avkid]

Originally Posted by mbenonis

Here's an article in Broadcast Engineering that summarizes the whole DTV/700 MHz spectrum issue very well:
http://broadcastengineering.com/audi...s_spaces_0307/

Ooohhhh, I like the chart:

[mbenonis]

I didn't even see the chart. I do feel obligated to point out one error on the chart though. The 902-928 and 2400-2450 bands are actually allocated to the Amateur Radio Service in the US, and licensed amateurs have priority over unlicensed devices (Wi-Fi, cordless phones, etc).

[museav]

A detail I have had pointed out to me is that at least up until now, the auctions of the 698MHz and above frequencies do not specifically require that devices like wireless mics cease operation in those bands, other than perhaps the public safety bands. There may be problems if you interfere with the licensed users in those bands but there may also be a lot of this bandwidth that is not used, at least for some time and especially in rural areas.

For example, I believe the Qualcomm bought the Channel 52 (698MHz to 704MHz) rights nationwide for their MediaFLO mobile TV service, but that may not be active in many geographic areas and apparently nothing would prevent you from using those frequencies as long as that use does not interfere with the licensed user. Some other bandwidth rights are being purchased for future technologies and may be open for some unknown time.

So I don't think that wireless mics operating at 698MHz and above will necessarily have to stop being used. I believe they will stop being sold and their use may be limited if the bandwidth is used in that area, but at least for now (or until the relevant laws change), for some people there may apparently be nothing preventing their use.

[mbenonis]

Originally Posted by museav

A detail I have had pointed out to me is that at least up until now, the auctions of the 698MHz and above frequencies do not specifically require that devices like wireless mics cease operation in those bands, other than perhaps the public safety bands.

Unfortunately, things aren't quite that clear. The sticking point is that wireless microphones are not Part 15 devices in the US, but rather Part 74 devices. Part 74 devices, defined in 47 CFR 74.800, may only operate on unused television channels. After February 2009, the spectrum from 698-806 MHz will no longer be allocated to television - so part 74 no longer applies. So the bottom line is, while you probably won't get caught immediately for operating there, you can't legally operate the device there - licensed or not (a whole other issue).

[museav]

Originally Posted by mbenonis

So the bottom line is, while you probably won't get caught immediately for operating there, you can't legally operate the device there - licensed or not (a whole other issue).

Which doesn't really change anything for the probably 90%+ of the total number of wireless mic users who are technically already operating illegally.

Here's the response I received last Saturday from a very knowledgeable individual when I made basically the same comment that you would not be able to use wireless mics in the "700MHz" bands after February, 2009 on another forum:

Not necessarily: as of the October 2007 revision to Part 74 and last Wednesday's FCC release of Amendment of Parts 1, 2, 25, 73, 74, 90 and 97 of the Commission's Rules to Make Non-Substantive Editorial Revisions to the Table of Frequency Allocations and to Various Service Rules still have BAS devices permitted to operate in channels 52-69.

As I understand it, the FCC has stated an intent to prohibit continued operation of Part 74 BAS devices, and specifically wireless mics, in the 700MHz bands but have not yet actually revised the rules to reflect this. I'm not arguing, more just agreeing on how unclear some of this still is.