315mhz or 433mhz FCC rules

Hi,
Can anybody help me understand the FCC rules on 315mhz or 433mhz wireless modules in US?

I don't really understand what its written in here

Basically I need to know followings
1. Maximum transmit duration
2. Minimum wait between two transmission or maximum number of such transmission in a given period.
3. Maximum transmit power in miliwatts
4. Data type restriction e.g. audio/video/random signal etc.

Also, is there any band (however tiny it is!) under 1Ghz frequency that is open to all in complete un-restrictive. I understand such band might be too crowded or noisy to do anything serious... but at least no worry about any regulation!

Thanks!

jay11421:
Basically I need to know followings

  1. Maximum transmit duration

See under "Any" in the table.

jay11421:
2. Minimum wait between two transmission or maximum number of such transmission in a given period.

I think you can interpret that as "periodic transmissions" if your transmit interval is significantly less than 50%.

jay11421:
3. Maximum transmit power in milliwatts

Whatever is confined within the specified field strength, which depends on antenna gain.

jay11421:
4. Data type restriction e.g. audio/video/random signal etc.

Audio/ Video is "Any". "Random signal" will be either periodic or intermittent, depending on what you mean by "random".

jay11421:
Also, is there any band (however tiny it is!) under 1Ghz frequency that is open to all in complete un-restrictive. I understand such band might be too crowded or noisy to do anything serious... but at least no worry about any regulation!

That is a rather silly question. You clearly have the rules in front of you.

Also, is there any band (however tiny it is!) under 1Ghz frequency that is open to all in complete un-restrictive. I understand such band might be too crowded or noisy to do anything serious... but at least no worry about any regulation!

I'm just curious about why your are concerned about regulation.

Are you building a commercial product?

Checking the FCC regs are not normally top of my list when experimenting with for example VirtualWire between two devices on 433Mhz.

Also 433 and 315 are not the only available bands, Though I'm not sure about the US, I thought there was a 915MHz band.

I know you mentioned "below 1GHz" but why do you need to stay below ?
There are great 2.4GHz modules that are very inexpensive, or you could look at Wifi (there are some interesting new inexpensive modules appearing for this band as well)

If its just for your own experimentation, you may like to consider getting a Ham Radio license, this gives you more options of bands (though it kinda depends on what you are doing).

There is no band that has no rules. Though some of the Ham bands - you would need an amateur license! - might allow more flexibility since they assume you know what you are doing.

Thank you Paul. but its still not clear to me! :~

Paul__B:

jay11421:
Basically I need to know followings

  1. Maximum transmit duration

See under "Any" in the table.

under "Any" it says 200 uV/m @3m, . is that means 3 minutes of continuous transmission?

Paul__B:

jay11421:
3. Maximum transmit power in milliwatts

Whatever is confined within the specified field strength, which depends on antenna gain.

is there any conversion table where i can get the number? say if i have a 2db antenna then what would be the maximum allowed transmit power? i'm saying it because on the module spec it says the card is 10 milliwatts but from the table it seems like it should be few hundreds micro watts :~

Thanks again.

rogerClark:
Are you building a commercial product?

nop! just some personal project. i'm sure a commercial product maker wouldn't ask all these silly questions!

rogerClark:
Checking the FCC regs are not normally top of my list when experimenting with for example VirtualWire between two devices on 433Mhz.

Thats not what it seems like from FCC documents and bulletins... it seems like they are very serious about these stuff. i have no idea how often they actually enforce it. i wouldn't be surprise if they do enforce it word by word... specially in big cities.

Thats not what it seems like from FCC documents and bulletins... it seems like they are very serious about these stuff. i have no idea how often they actually enforce it. i wouldn't be surprise if they do enforce it word by word... specially in big cities.

Its your call.

However I suspect there are a large number of wireless devices in use, especially ones bought from eBay (from overseas - you can guess where I mean..... ) that don't conform to FCC rules.

If you buy a module legally from a reputable supplier in the USA, it will operate on the correct frequency and should conform to the correct power limits.

Then the only thing you need to worry about is the time domain i.e what percentage of air time are you using.

rogerClark:
If you buy a module legally from a reputable supplier in the USA, it will operate on the correct frequency and should conform to the correct power limits.

Then the only thing you need to worry about is the time domain i.e what percentage of air time are you using.

yes that would simplify things a lot. although i'm yet to find an FCC certified module!

anyway
I think i found the FCR 47 document they mention on the table... §15.209 and §15.231

what i gather... here is the summary

For contiguous transmission ------ maximum 200 micro volt/m at 3 meter distance
For Maximum 5 seconds (manual 10 sec) duration transmission (can not be periodic) ------ maximum 12,500 micro volt /m at 3 meter distance
For Maximum 1 second duration, for period transmission (wait time 30 times of transmission time) ----- maximum 5,000 micro volt/m at 3 meter distance

now in order to calculate the actual transmission power... i guess i have to buy a Field strength meter :frowning: $$$

Please correct me if i understood anything wrong in the above.

Thanks

@jay11421

I think you better divulge a bit more information about what you are trying to do.

If buying from one of the big reputable suppliers e.g. Adafruit or Sparkfun is not good enough for you from a legal standpoint I suspect you will find difficulty meeting your requirements in what is essentially a hobbiest sector.

I did a quick search and Adafruit sell a load of 315Mhz stuff Search Results for '315mhz' on Adafruit Industries
and sparkfun sell 433mhz
Search Results for 433 - SparkFun Electronics
and 315mhz
Search Results for 315mhz - SparkFun Electronics
and 915Mhz
Search Results for 915mhz - SparkFun Electronics

However if you want to send streaming data, I think you could let us know, as in which case you’d probably need to use the video transmission frequency bands, and I’m not sure what hardware is available to send raw data on those frequencies (though there are plenty of video TX’s)

Just a thought, have you tried Farnell, or mouser etc, they are normally sell items that are fully legally compliant

No affordable field strength meter is going to tell you any kind of reliable measure of uV/m. Plus an anechoic radio chamber.

under "Any" it says 200 uV/m @3m, . is that means 3 minutes of continuous transmission?

You've figured out now that this is a measure of signal strength, yes? 200uV/m measured at 3meters distance?

This part I think excludes you from altering the transmitter in any way, including the antenna:

Section 15.203
In order to prevent such interference problems, each Part 15 transmitter must be
designed to ensure that no type of antenna can be used with it other than the one used
to demonstrate compliance with the technical standards. This means that Part 15
transmitters must have permanently attached antennas, or detachable antennas with
unique connectors. A "unique connector" is one that is not of a standard type found in
electronic supply stores.

It is recognized that suppliers of Part 15 transmitters often want their customers to be
able to replace an antenna if it should break. With this in mind, Part 15 allows
transmitters to be designed so that the user can replace a broken antenna. When this
is done, the replacement antenna must be electrically identical to the antenna that was
used to obtain FCC authorization for the transmitter. The replacement antenna also
must include the unique connector described above to ensure it is used with the proper
transmitter.

What you are reading is really more for an EE and GROL license holder who is designing a Part 15 transmitter.

What is it you are trying to do? Digikey, Mouser, Jameco, Seeed Studio, Sparkfun, Amazon, and others sell RF modules. Presumably, if they weren't legal, they'd have been stopped by now. As far as FCC certification, those are unlicensed bands as long as they stay within the confines of the regulations, so I don't think the FCC certifies them.

Since wireless LANs, Bluetooth, and ZigBee have been introduced, much of the design effort within the unlicensed spectrum in the U.S. has been focused on the 2.4-GHz band. But other unlicensed bands that the Federal Communications Commission (FCC) set aside for industrial, science and medical (ISM) applications also have a lot to offer design engineers who need wireless links for short-range audio and video transmission, as well as a variety of remote control, metering and sensing applications.

FCC regulations for the 915-MHz ISM band, for example, place no restrictions on type of application or duty cycle. In addition, the power output permitted by the regulations is considerably higher than it is in other portions of the ISM spectrum.

915 MHz is the center frequency of the band bounded by 902 and 928 MHz. Within this band, FCC regulations allow 50 mV/m electrical field strength, at a distance of 3 meters from the transmitting antenna.

Oh, and we can't tell you the power in milliwatts, as it depends on the transmitting antenna, too.

antenna gain is essentially 0, unless you go buy a yagi.
Often the gain is quite negative, e.g., with those helical springy coil antennas.

With an easy to get Ham license, you can operate to your heart's content in the 70cm band, using $4 HopeRF RFM22, RFM69 modules. Not all regions have the 70cm ham band.

And RadioHead is a nice ready to go protocol stack, upto an option for meshing.

jay11421:
under "Any" it says 200 uV/m @3m, . is that means 3 minutes of continuous transmission?

It clearly does. Audio and video senders are an obvious examples of continuous transmission, whereas slightly higher power levels are permitted for low and very low duty cycle (that was the word I was looking for earlier) transmission.

jay11421:
is there any conversion table where I can get the number? say if i have a 2db antenna then what would be the maximum allowed transmit power? I'm saying it because on the module spec it says the card is 10 milliwatts but from the table it seems like it should be few hundreds micro watts

I'm sure there are such tables, but I certainly don't know where. Theoretically I should, as the regulations now specify "safe" radiation levels for communications antenna installations.

jay11421:
That's not what it seems like from FCC documents and bulletins... it seems like they are very serious about these stuff. i have no idea how often they actually enforce it. I wouldn't be surprised if they do enforce it word by word... specially in big cities.

They are serious about instilling a healthy level of fear into miscreants. In practice however, this only swings into effect when a complaint of interference is made. Generally on (regarding reception within) the ISM bands, such complaints are politely and automatically rebuffed unless they perceive that there is a real problem, since acceptance of interference is part of the "deal" when using ISM bands.

Paul__B:

jay11421:
under "Any" it says 200 uV/m @3m, . is that means 3 minutes of continuous transmission?

It clearly does. Audio and video senders are an obvious examples of continuous transmission, whereas slightly higher power levels are permitted for low and very low duty cycle (that was the word I was looking for earlier) transmission.

It clearly does NOT mean 3 minutes. That is referring to field strength at 3 meters distance from the antenna.

I am not aware of any limits, as several devices that fall into the category of low-power, non-licensed transmitters such as cordless phones, baby monitors, etc are not time limited in any manner.

I was referring to the "Any" - which would include one minute, three minutes or several hours.

Yes, of course "3m" is three metres, and cannot be interpreted in any other way. :smiley: If you want to specify minutes, that would if anything be "min".