FCC rules about RF data transceivers?

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I am working on a one off project for my home that will monitor items
(like temperature and humidity) in several out buildings and have a
status display in the house.  There is buried power wiring in the way so
I don't want to try putting in underground cable.  Lightning is also a
concern.  I'm on a high spot and have had three tree's hit in 12 years.

An RF data link sounds like an answer.

Ready made RF modules like the MaxStream XC09-009WNC (900MHz) sound
good.  Probably enough range, plenty fast at 9600 bps, not too expensive
and they look easy to use at first glance (no spec like make the data
bits average out to 50% bits on).

The docs for the module says "Devices that embed XCite Radio Modems can
inherit MaxStreamís FCC certification".  Does that mean if I follow the
manufacturer's rules on antennas and labeling I can use this in the US
without doing any testing?

The prepackaged RF modems would certainly work and take care of the
testing and certification worries.  But the ones I've seen are all over
$200 each, which is more than I'd like to spend when I will be getting 3
transceivers to start.

Thanks for the help.

Gerald Bonnstetter

Re: FCC rules about RF data transceivers?

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More than 40 years ago I worked on a college radio station which
"broadcast" a "carrier current" signal. IE impressed a AM broadcast band
signal on secondary side of "pole transformer". Have no idea of current
regulations but suspect is still allowed. Wouldn't this be same as
X10(?) remote controls?

Re: FCC rules about RF data transceivers?
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My original plan was to use an X10 command that can transfer data.  But
it is only 2 bytes at a time and very slow.  About a byte a second.

That might not be too bad with very little data, but the "it sure would
be nice to have..." added a bit more data.  Then I realized that I would
have to worry about collisions between the X10 transmissions I was using
for some lights.  Still would be doable but I would need to build my own
X10 controller into the status display so it could synchronize data
transfers in between X10 lighting commands.

But there are "phone line" through AC modules that could be used.  I had
considered it, but all the modems and modem chips I was finding seem to
be for 56 K bps anymore so are rather costly after getting the "phone
line" through AC modules.  It would save on the certification worries as
I wouldn't be connecting to a real phone line on either end.  And with a
little luck, maybe I could design a bit banging "modem circuit" to send
data without a real modem.

Re: FCC rules about RF data transceivers?
$aqh$ snipped-for-privacy@news.netins.net:

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 Without a specific FCC radio license you would be constrained to a PART 15
certified device.  I suspect everyone who makes such a device like the
XCite unit would not be cheap since they had to get their units certified.
If you do not use their recommened antenna configuration or modify the
radio in any way and someone complains about interference the fines can get
pretty big pretty quick.  Of course you can design you own unit and get it
certified, but it will cost you many $$$$.  So you choice is pay a little
more an be safe or take a chance you will not get caught.


Re: FCC rules about RF data transceivers?

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Or maybe I should look into getting a Technician Class then I would have
a license.  No code now so I could probably do it.  Also might be
helpful in emergencies.

Hum, I wonder if any micros have a UART that does Morse Code?  ;-)  No,
wait I couldn'y use that without learning it myself.

Re: FCC rules about RF data transceivers?
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As far as the "intentional radiator" requirements of FCC Part 15 goes, that is
exactly what it means.

If I understood your note correctly, you are building these for personal use and
can claim exemption in 15.23 for homebuilt devices to Part 15.  That exemption
is good for up to 5 units.  If you were planning to market these, you would
still have to meet the "unintentional radiator" requirements of  FCC Part 15.
For your reference see
<http://www.fcc.gov/oet/info/rules/part15/part15-61305.pdf .

Also, I think you should probably use the XC09-009NSC MaxStream module since it
has a Reverse Polarity SMA connector on it.  Design your electronics so that you
plug the XC09 module into it and then just mount it so that the RPSMA connector
sticks out of the box.

James T. White

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