2.4ghz FCC license requirements?

[MarkWebber]

I've seen various mw numbers quoted as being FCC compliant for unlicensed use. Attempting to search for an answer within the FCC sight provided no worthwhile results :roll: Does anyone have a link to a specific answer.

Thanks

[PaulH]

According to this:

http://www.fcc.gov/Bureaus/Engineering_Technology/News_Releases/2001/nret0104.html

100 mW is the maximum output power for an unlicensed transmitter.

According to this:

http://www.arrl.org/FandES/field/regulations/news/part97/d-305.html#311

100 Watts :!: is the maximum output power for a spread spectrum transmitter, but shall be variable and limited based on the SN ratio if more than 1 Watt is needed.

[Raven_darkcloud]

2.4g is open use, no license requiered.

[PaulH]

Raven,

You're just quoting the same "common knowledge" that everyone else does. Where's your proof? Show us some links to read.

[MarkWebber]

I'm with Paul. I've tried to read through the mess on the FCC site. I prefer a difinative answer. I've seen limits as high as 1watt for channel hopping tx. That doesn't really apply to us. And the links that Paul put up are supported elsewhere.

Pity the governing bodys can't make it more b/w for us. :dontknow

[oscillator]

2.4GHz is part of the ISM - industrial scientific and medical "unlicensed" band and falls under FCC rules part 15. See part 15.247 for maximum power restrictions.

The simple answer is 1 watt or 30dBm. However, antenna gain is also a factor, and Effective Isotropically Radiated Power (EIRP) is limited to 36dBm (4 watts) assuming a 6dBi antenna. The FCC allows the antenna gain to be increased by 3dB for each dB the radio output is lowered, thus if you decrease the output power to 21dBm and use a 32dBi gain antenna, you are allowed 53dBm EIRP.

So I guess the real answer is, it depends.

Update: OK, here is the full FCC part 15 - happy reading!
http://www.fcc.gov/oet/info/rules/part15/part15-8-14-06.pdf

[enigma]

I just ordered a 1.240ghz 100mw tx/rx that claims you need a license. What is the limit? 100mw? Now I'm confused! Has anyone used this before?
http://www.boostervision.com/cart/scripts/prodView.asp?idproduct=104

[MarkWebber]

Here's what I have trouble with:

Page 101. subsection (iii)
Frequency hopping systems in the 2400-2483.5 MHz band shall use at least 15 channels. The average time of occupancy on any channel shall not be greater than 0.4 seconds multiplied by the number of hopping channels employed.

The whole part 15.247 section deals with frequency hopping system maximum transmission levels. None of the downlinks I've looked at are frequency hopping. Most only have 4 channels at best. I still haven't found a section that directly indicates maximum transmission levels for transmitters like we would be using. :dontknow

I think I'm getting a headache :arggg:

[enigma]

They don't make doing the right thing easy, do they? I wonder how many people actually get a license for these, and how they go about it.

[MarkWebber]

I'm sure it's like most things of this nature. Most probably don't worry about getting the license. However, I'm the guy that gets caught doing anything wrong so I want to be sure which P's and Q's to mind. It's sad that a document containing 155 pages can't contain any clarity. Clarity seems to be elusive to our regulators!

[enigma]

Would it be the same as the license that's required for the 10 mile walkie talkies?

[oscillator]

The 10 mile walkie talkies are GMRS (General Mobile Radio Service) and are ~150MHz (just above the 2m ham band) and similar to the FRS radios, so I doubt it is the same license for 2.4GHz.

Most of the FCC regs are for people building commercial equipment to sell. If you are planning on selling something, yes, I would absolutely make sure you were in strict compliance.

That said, since 2.4GHz is an unlicensed band and is considered ISM (industrial, scientific and medical), there is all sorts of stuff that operates here - microwave ovens, WiFi, Bluetooth (what I do), plasma generators for chemical vapor deposition, etc, etc.

If you built something for your personal use in this band that did not knock out everyone's WiFi on the block or cause major interference issues, I doubt anyone would care. Since it is an unlicensed band, communications equipment here must be robust to deal with all sorts of potential interference.

While there are plenty of CW (continuous wave) devices like microwave ovens and plasma deposition machines that leak emissions into the 2.4GHz band, all the communications devices I am aware of in this band are spread spectrum. I may be wrong, but I don't think the FCC allows non spread spectrum communication devices in this band. If they do, it will be somewhere in part 15.

[oscillator]

Mark,

I just went back and read your original post. There is no mention of 2.4GHz (or any other frequency), so not sure how we got on the 2.4 thing. Sorry about that.

Perhaps you could tell us more about what you are trying to accomplish and we might be able to help you better. Feel free to PM me if you don't want to broadcast your plans.

What bands you can use at what power and what modulation requirements will depend on if your use is personal hobby, commercial, or selling equipment for one of the above. Obtaining an amateur radio license opens up all sorts of bands for personal hobby use, but commercial use is not allowed.

There are also off the shelf communications "modules" that may be useful depending on your application, and then there is modifying existing equipment. The data rate you need to support and the range you require will also be factors. Power is only one way to address the range issue - higher gain antennas, more robust modulation, and lower data rates can also improve range.

Hope this helps...

[MarkWebber]

Sorry, the 2.4 mention was only in the topic header.

Anyhow, I'm just looking to do the same as everyone else for a downlink. Definately qualifies us as commercial as we are selling the photo/video results, right?

[enigma]

stumbled across this site today, it has a few links for license info, as well as other interesting info on AP
http://www.hicam.com.au/art_lic.htm

[oscillator]

Mark,

yes, that would be commercial use. The link posted by enigma describes privileges available with a HAM licence - which is non commercial use only.

Unless you have an extensive RF background, you are going to want an off the shelf system. Such a system will either state it is unlicensed, or if a license is required the mfg or the retailer will provide some information on how to apply for the license. The vast majority of systems will be unlicensed aimed at joe consumer. The licensed systems will be industrial quality and likely too heavy or bulky for your application.

So what to do?

You can vastly improve the unlicensed system without braking any rules. The best way to do this is with a high gain antenna on the receiver. Since the RX does not transmit, you can make the antenna as high gain as you like and not violate any regs. Commercial antennas abound, but you can make a very good RX antenna with a tin can. Just google "2.4GHz can antenna", "WiFi tin can antenna" something similar. (Note: the classic Pringles can design is not very good, so make sure whatever design you choose has measured gain values. I've seen claims as high as 9dB!).

A 9dB RX antenna gives you 8 times the signal power over a dipole (0dB gain) and should significantly improve your range. With a commercial antenna you could get even higher gain. Note that this means the antenna will be highly directional. Not a problem as you can point the RX antenna at the heli.

The TX antenna is a slightly different story. Here you want an antenna that only radiates down. Such an antenna has 3dB gain. This insures there is no wasted energy going up (skyward). You can purchase a commercial antenna like the one in this thread: http://www.helifreak.com/viewtopic.php?t=23050 , or you can simply place a reflector behind your existing Tx antenna.

Range will be based on the following factors:
1. TX power
2. TX antenna gain
3. Data rate (lower data rate = longer range)
4. Transmission loss path (vacuum (space) is best case)
5. Interference sources (the more "noisy" the airwaves, the lower the range)
6. RX antenna gain

So...looking at these case by case:

1. TX power is limited by regulation. Furthermore, adding a power amp to an existing system is non trivial requiring proper impedance matching.
2. As discussed above, 3dBi is the most you can take advantage of here, unless you want to devise a system that always points the antenna at you!
3. If you can live with lower frame rate or lower res (and your system will let you adjust these parameters) you may find your range improves.
4. Expect decreased range on humid days.
5. Not much you can do about this one unless you can identify the source of the transmission and get it turned off.
6. Get the highest gain antenna you can and keep it aimed at the TX antenna.

Hope this helps!
Mark

[billyd]

I looked into getting a license and it's difficult and time consuming. For what most of us are using this for, getting a ham license to be in strict compliance for wireless ap, would be like going to college to get an electrical engineering degree so that you could make toast.

Thanks, but no.

Also, our sub one watt transmitters (mine's 500 mw) aren't going to draw much attention unless you happen to fly over the governor's house while he's surfing the net with his wifi phone.

What the FCC should have is a license available to rc'ers which entails paying some nominal yearly fee and signing off a user responsibilities form which if violated would result in a fine or other appropriate action. But instead we have to become a surgeon to cut a toenail. Got to love big government.