Re: Low cost Radio tranceiver Range :5Km Baud Rate : 19200-115200baud

From: Paul Keinanen (keinanen_at_sci.fi)
Date: 07/13/04 

Date: Tue, 13 Jul 2004 13:35:43 +0300

On Tue, 13 Jul 2004 19:32:38 +1000, <Poniasahgsour Uryeghama> wrote:

>I'm looking for "Low Cost" radio tranceiver with 5Km range and full-dublex
>19200-115200 baud rate. Would you suggest one?

A full duplex system requires two separate radio links, one for each
direction. To avoid the problem with duplex filters, use two complete
separate unidirectional radio links operating at different frequency
bands.

A 5 km range is easy, if you have a _guaranteed_ line of sight, but if
not, it becomes quite tricky to get a decent reliability, requiring a
lot of power (several watts), special modulation and coding systems to
avoid selective fading etc.

Then you have to consider in which countries this system should be
operated and check separately for each country which frequency bands
can be used for this kind of operation. Remember, you need two
separate bands, if you insist on full-duplex operation.

It would be easiest if some license exempt bands could be used, but
these are usually limited to 10-100 mW, which would not be sufficient
for reliable 5 km non-light of sight paths at those speeds. Also note
that there are usually a lot of all kinds of other activities on
license exempt bands that could block your link at much shorter
distances, thus, you may need some frequency hopping or spread
spectrum system to avoid the other users.

For reliable systems, most likely a licensed radio system would have
to be used, with type accepted devices and separate licenses for each
installed transmitter. Depending on your definition of "Low Cost" this
may or may not be acceptable :-).

Paul

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