On Wed, 23 Aug 2000, Miguel Angel Heredia Moreno wrote:

> for the FM transmission first post ... consider this :
>
> 1) You got 50-100 people around a city working office-time jobs
> 2) Each one of them collect about 20 numbers every minute
> 3) They mut send this and verify they were received well and store them locally
> 4) They need this units to be mobile (no car)

Tall order, especially if you need it done cheaply.

> theres another way to do this than packet radio ?

Sure.  Does it **HAVE** to be done in real time?  I bet not.

If it's got to be done in real time, you're looking at possibly 100 * 20 =
2000 messages, plus ACK packets, for a total of 4000 packets per minute,
or roughly 67 packets per *second*, assuming no retries or collisions. To
say that would be difficult to engineer would be an understatement.  You
would need to be running very high data rates on UHF with several Watts at
the very least, and I doubt even that would work.  The battery to keep a
radio delivering that kind of duty would be heavy, too.

If it's got to be fast but not real-time, you could store up X amount of
messages from a remote and send them in a batch.  You would still wind up
with a pretty busy channel.  Send a packet every five minutes, maybe.
Then you could get away with 1200BPS at VHF, and 1200 is a *lot* easier to
get working reliably than 9600 or higher.

If it doesn't have to be real time, why not a small, portable, non-radio
device to store the information during the day and uplink it via modem, or
even by packet radio, at night?  If real-time is not a requirement, I
would trade lots of on-board RAM and occasional uplinks for the complexity
and cost of a radio solution.

Just some ideas for you.  I love radios.  I love working solutions even
better, though.

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
                -- Isaac Asimov

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