>
>
> - For all I know, I need FCC certification of the transmitter. Due to the
> small quantities (and the lack of experience I have with this), it seems
> to
> me that getting my own is not going to make much sense. OTOH, it seems
> that
> with something like these Laipac <http://www.laipac.com/easy_315a_eng.htm>
> or Linx modules http://tinyurl.com/yks8c3,


RF digital also does certified modules.


> - I'm not sure whether one-way transmission will be good enough. I want to
> get close to 0 false positives at the receiver, and false negatives should
> ideally be less than 1 in 1M. Is this realistic with one-way transmission?
> Or would I need transceivers and a protocol? (In this I'm not considering
> concurrent presses of switches connected to the two transmitters.)


The RF digital boards use CRC'd packets, so if they get a packet, it's
valid.


- In case running my own FCC certification doesn't make sense


Big bucks.
I've not done this end myself, but it's supposed to be that if you use a
pre-certed module and antenna, that you don't need cert beyond part 15.

- I'm thinking about using Lithium coin batteries (like CR2354 or so, size
> depending on what I end up needing for the transmitter/transceiver). Is
> this a good idea? Any better suited alternatives? They should be
> user-replaceable. I'm not sure how important it is that they are readily
> available, but it would be a bonus if they didn't have to order the
> batteries from us.


They really don't like pulses of current, even at the 20mA level.

- Last not least is the antenna question. I'd like to come by without any
> antenna external to the (very small) enclosure. The MaxStream module comes
> in a version with what they call a "chip antenna". Its performance seems
> to
> be just fine for my needs. Is this more than just a skillfully placed
> track?


There is no "magic" in antennas.  Remember, a 50 ohm resistor will show a
1-1 VSWR with a 50 ohm source, but it's a really poor antenna. :)    If the
antenna is small, you're giving up gain.

A while back, I had the pleasure of fighting all the bigwigs in the company,
because they wanted to use this magic "chip antenna".  Very high gain it
said, and $7 each so they MUST be real good, right?
A small track on the PCB gave far better results. "High gain" in this
company's language meant -10dBi maximum, and in most directions
significantly less.

When you see an antenna gain figure posted, if it dosen't say dB(something)
then assume it's dBi.
Also know that this is the peak gain, and gain in other directions of the
sphere will be less.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist