At 10:56 p.m. 23/08/00 -0500, you wrote:
>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.

No, I can afford a little delay, lets say : the guy is in the street with
his unit and put the numbers in and it say : "wait, busy" and then he
retries till its ready, lets say about really 10 numbers per minute.



>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.

I was taking this in account too, to upload the data in the evenings but,
Wouldn be more problems if ALL them send ALL their data around a time ? it
wouldnt be better if they upload piece-by-piece bytes of data every few
minutes ?



>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


Thank you Dale, a lot! :)



>---
>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
>
>--
>http://www.piclist.com hint: The list server can filter out subtopics
>(like ads or off topics) for you. See http://www.piclist.com/#topics

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.