On 7/24/2012 2:41 PM, Jeff Liebermann wrote:
On Tue, 24 Jul 2012 12:57:33 -0500, John S
wrote:

On 7/24/2012 12:12 PM, Jeff Liebermann wrote:

Microwatts doesn't seem to make sense as there are products being sold
that advertise 10mw and 100mw output power levels. Obviously they are
not being certified under Part 15. However, I can't find another US
service on 433MHz that qualifies (except ham radio). FCC frequency
allocations table is of no use:
http://ecfr.gpoaccess.gov/graphics/pdfs/er27ja12.018.pdf
433MHz is an ISM band, but only in region 1 (Europe) and not in region
2 (US).
http://en.wikipedia.org/wiki/ISM_band
My guess(tm) is that the higher power 433MHz devices can only be sold
in Europe. Yet, that's not apparent on any of the sites selling
433MHz data radios.

It appears that we have both looked very hard and have come to the same
conclusion. I now wonder if the US suppliers are unaware of the region
1/region 2 thing.

I still have some more reading to do, and ask a few experts. However,
offhand, methinks there's a problem.

"FCC Compliance testing Using the MICRF112"
http://www.micrel.com/_PDF/App-Notes/an-55.pdf
Page 9 has the calcs for a typical key fob transmitter.
36 microwatts.

I saw that. Lower left corner of page 4 says that continuous operation
is allowed. Where do they get that?

It's there, although I had to read it several times before I found it.
http://louise.hallikainen.org/FCC/FccRules/2012/15/231/
See section (e):
Intentional radiators may operate at a periodic rate exceeding
that specified in paragraph ...

Yes, but continuing with paragraph (e) includes the last paragraph which
you quoted earlier:

quote you

See the last paragraph of 15.231
http://louise.hallikainen.org/FCC/FccRules/2012/15/231/
In addition, devices operated under the provisions of this
paragraph shall be provided with a means for automatically
limiting operation so that the duration of each transmission
shall not be greater than one second and the silent period
between transmissions shall be at least 30 times the
duration of the transmission but in no case less than 10
seconds.

/quote you

And this last paragraph is part of FCC paragraph (e).

There is nothing in that section which allows continuous transmission.


The field strength is limited to about 4500 uV/meter. There's also
some notes on the topic on Pg 14 of the TI app note:
http://www.ti.com/lit/an/swra090/swra090.pdf

It is parroting paragraph (e). Nothing new nor informative there.

I'm enjoying this, Jeff. Finally, I have someone with which to kick this
around and learn something. I'd really like to get to the bottom of this
whole thing.