Reply to "Stay Away from 900MHz band"

[Landon2006]

There was recently a post on here titled “Stay Away from the 900MHz wireless Mics”. I would like to reply to that. The entire 900MHz band is not licensed by the FCC. In fact, many cordless phones operate on the 900MHz band.

900MHz and 2.4Ghz are both unlicensed bands in the united states, from what I have been able to gather.

I know about the 944-954 MHz band is licensed, but not the entire 900Mhz band. If I recently recall, there are Sony wireless mics that operate in the 900Mhz band, but not that high in the band.

I have a cordless phone that operates at 900MHz, and the 2 way radios we use for communications offer 1,000 channels in the 900MHz range.

Can you clear this up for me?

 

[mbenonis]

Sure, I'd be happy to. I am specifically warning people to stay far, far away from the 944 MHz band, because it is licensed and very fragile links are there (for instance, most radio stations use this as a point to point communications band to get their signal up to their transmitter site).

The 902-928 MHz band is also a licensed band (actually, licensed for radiolocation and amateur radio use first, and then for ISM* use. After those users, unlicensed use is permitted under Part 15 of the Commission's rules. The catch here is that to qualify for Part 15, you need to use relatively low power. You must also accept interference from other users (such as amateur radio, etc), and not cause anyone else interference.

I know of only one wireless mic system that operates in the 902-928 MHz band, made by Line6. It's a digital system, and based on a cursory look it's primarily for guitar players for use in their garage. I certainly would not use it in a stage show.

Lectrosonics makes 944-952 MHz gear, as does Shure (I believe). Sennheiser may as well. But like I said, do not buy it. You may ask, why would they make it if it's a bad idea to buy it? TV stations may have a legitimate interest in this gear for remote operation (i.e., anchor out in the field). TV stations coordinate the use of this frequency with their regional frequency coordinator to ensure that it does not cause interference, and they also hold an FCC license for the frequency to ensure that they are protected from harmful interference. We, as theatres, are not eligible for such a license (see the FAQ for why).

*ISM - ISM stands for Industrial, scientific, and medical applications. These are NOT communications systems, but rather other uses of radio waves for, say, heating, manufacturing, medical, or research purposes. Think microwave oven. Many people have this confused with Part 15 devices, such as Wi-Fi access points. They are just that - Part 15 - and not ISM.

That clear it up hopefully? If not, keep asking questions!

 

[Chris15]

Whilst I will not get into stuff I don't understand nor want to understand that is the current US regulatory situation, let me say this. If you are proposing that because your cordless phone works in that band, then you should use a radio mic in that band, I have to start asking questions.

To me, using a frequency that is liable to have spurious noise generated at a moment's notice, ie. by someone using a phone, sound like a recipe for disaster mid show. Ditto if someone can insert radio noise over the top.

 

[FMEng]

Just because somebody sells it doesn't make it a good idea to buy it. I sure wouldn't try to run wireless mics in a band full of part 15 users. It is just asking for trouble. A cordless phone is a bit less demanding than a wireless mic, so what works for one may not for the other.

As a broadcast engineer, let me add my voice to what Mike says about 944 systems. Using equipment in that band is likely to get a visit from the FCC or, at the very least, a very unhappy engineer who has lawyers. In my opinion, systems should not be sold on those channels without proof of a valid license to use them.