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FCC Regulations???

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Buddie

New Member
I have built a project that uses a TWS-434 Transmitter and RWS-434 receiver and Linx LS encoder/decoder that remotely controls the operation of a relay. This is just for use in my own house. Does anybody know if there are any FCC regulations for this application?
Thanks!
 

ke5frf

New Member
Yes indeed there are FCC regulations. Under Part 15 rules, technically, you can operate "intermittent control signals" in the 70 cm UHF band from 410-470 Mhz. I would refer to and familiarize myself with this FCC bulletin to know the rules:

https://www.electro-tech-online.com/custompdfs/2009/12/oet63rev.pdf

Here is the deal though. Be aware that this frequency is smack in the middle of the 70 cm AMATEUR RADIO band. Amateur Radio is the primary user of this band segment. Your device MUST NOT cause interference with "ham" transmissions. For instance, if your next door neighbor happened to be an amateur operator, he would have priority and a legitimate right to file a complaint if your transmitter interfered with his equipment. Generally speaking, many wireless devices operate control signals in this segment...ie alarm keyless entry, garage doors, wireless fans and lamps, etc. A very low power UHF transmitter will not create a strong enough signal to interfere with much and the "blips" of remote controlled signals like this are trivial. So as long as you do not modify the device or attempt to increase its power or use an unapproved antenna of your own design (with gain), you should be OK.

One more thing to be aware of. Amateur Radio being the primary allocant of this band is not bound to concerns of interfering with your device. If your ham neighbor keeps opening and closing your garage door when he transmits, for example, it is unfortunately something you have to live with. Any good ham, and most are, will honor the integrity of his license and if you politely ask him he will ensure his equipment is properly functioning, installed correctly, and radiating a clean signal. But that is just about all you can expect or ask being this is his frequency allocation as a primary user. UHF transmissions are usually FM and are somewhat wideband so that he need not be directly on your frequency to cause a problem.

I encourage you, if you are interested in radio technique, to get your own license an become a ham. It is fun. Note though that having a ham license doesn't legitimize a part 15 device making it "primary use" equipment. It does permit you to modify it however if I'm not mistaken if it is within an amateur allocation.

FCC: Wireless Services: Amateur Radio Service: Amateur Home
 

Buddie

New Member
Thanks for the info. It seems that I'm okay if I'm under a certain power, but I do not understand how to know my power. My datasheet says that at 5 to 6v the output power into a 50Ω antenna is 14 dBm. I am using 3.3v and a piece of wire for an antenna (≈30-35 cm). Would this be low enough? I am fairly sure that I am using a intermittent control signal, but the transmitter is always connected to power. So am I correct or not?
Thanks.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks for the info. It seems that I'm okay if I'm under a certain power, but I do not understand how to know my power. My datasheet says that at 5 to 6v the output power into a 50Ω antenna is 14 dBm. I am using 3.3v and a piece of wire for an antenna (≈30-35 cm). Would this be low enough? I am fairly sure that I am using a intermittent control signal, but the transmitter is always connected to power. So am I correct or not?
Thanks.

As it's a licence free radio module, simply follow the instructions that came with it - or are on the datasheet for it.
 

ke5frf

New Member
OK, basically you are using a Part 15 device that is built to a manufacturer's specification. They specify 14 dB which is about 25 mW.

The formula they give for calculating compliance is essentially to arrive at "effective radiated power". This includes the gains and losses associated with the entire circuit including the antenna at a reference elevation. They are using 3 meters above grade it appears. They want you to comply with 200 uV/m or therabouts. To calculate your compliance these antenna, amplifier, and loss variables have to be known.

I think the formula goes something like:
V/m= sqrt[30*P*G]/r,

But I wouldn't stress over doing this calculation.

Being that this is a commercial device, it should be certified by the FCC. The caveat is that you are following manufacturer's specifications. Is the antenna you are using supplied with the device, or if not did you make it to their specifications?

Honestly though, I wouldn't worry myself a whole bunch if you aren't using a gain antenna like a yagi on a 100 ft tower. 25 mW isn't much. You likely will never bother a soul. Just be prepared to throw the thing in the trash if you are unlucky enough to interfere and get reported by someone.
 

Mr RB

Well-Known Member
The rentron website says the transmitter is "up to 8mW".

These are a cheap and proven RF module pair, I thought of using about 20 of them around the house for a heap of home automation sensors but maybe that would contravene "intermittant use" if they were all pinging away every couple of seconds.
 
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