Could you not turn down the TX power of the module and it would then
be OK to have it closer than 20cm to a person?

As for using Zigbee one-way: Zigbee is a protocol layer on top of the
IEEE 802.15.4 physical/link layer. Most Zigbee modules will work in a
dumbed-down mode where they are only using 802.15.4. In that mode, you
can usually turn retries down to 0 so it won't continue to try to
transmit a packet if it doesn't get a response. Similarly, on the RX
side, you could make some adjustments to prevent transmit (like
setting the channel clear threshold so low that it always thinks the
channel is busy).

Sean


On Thu, Jul 8, 2010 at 4:42 PM, Harold Hallikainen
<harold@hallikainen.org> wrote:
>
> I need a one way RF link. I'm considering use of 915MHz, but I can not
> find any transmitters with FCC modular transmitter certifications
> (http://louise.hallikainen.org/FCC/FccRules/2010/15/212/ ).
>
> Section 3.1 of http://ww1.microchip.com/downloads/en/DeviceDoc/70329b.pdf
> states that the MRF24J40MA has certification as a modular transmitter.
>
> I COULD go Zigbee all the way, except that the "receivers" would generally
> need to transmit back to the "transmitter" where the data originates.
> Section 3.1.1 of the datasheet requires the antenna be 20cm or more away
> from people. This disallows a handheld or portable "receiver."
>
> So, what about the possibility of operating one MRF24J40MA as a
> transmitter and multiple MRF24J40MA modules as receivers where the
> receivers NEVER transmit? Has anyone tried anything like this? Is it a
> good or bad idea?
>
> THANKS!
>
>
> Harold
>
>
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