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26/27Mhz RS-232 Transciever Design...

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Jethro

New Member
I need a design to transcieve RS-232 data from a Laptop to a PIC system. I am quite clued up with digital electronic systems, but have a scant knowledge of RF communications systems. The reason for these frequencies is the availability of antenna's and hardware for CB's. (26Mhz here in NZ) Parallax Inc have several Serial Transcievers designed for use with their BASIC Stamp products, but the prices are out of my reach and I don't see any reason why I can't make my own...

- Baudrates need to be at least 2400, asynchronous.
- Range needs to be at least 100m line of sight. Supply power for longer range is not a problem.

Unfortunately I don't have a clue as to where I should start, so I'd really appreciate it if someone could push me in the right direction. A link to information and specifications of RF digital transmission or whatever.

Thanks
 

stevez

Active Member
Sorry I can't provide URLs for on-line stuff but I can tell you that radio amateurs (hams) do plenty of data communications on various bands including those near 26 mHz. Radio Amateurs Handbook by ARRL might be a good reference. There are certainly other ham radio handbooks that would be good resources as well. At least it's a place to start. Be aware that regulations relative to RF transmission may exist.
 

mechie

New Member
RF comms?

Just before you get too entrenched in a particular frequency...
just a bit further up the spectrum (just below 1/2 Gig :shock:)
take a look at EasyRadio ER400TRS this little beastie does a lot of the housekeeping for you.
Around £25 (UKpounds) or $60 (US) each.
Aerials are small and easy to make, range is claimed as 150m+

Or take a look at RF Solutions (http://www.rfsolutions.co.uk/), they do an excellent book, "An Introduction to Low power Radio". This is well worth getting to find out why RS232 cannot be fed directly into a transmitter (the EasyRadio modules have a processor onboard to deal with issues such as preamble for you so they literally work straight out of the box :) ).
This little book is well worth reading regardless of your chosen frequency.

Both items are available from Radio Spares (http://rswww.com/) in the UK.
New Zealand website at www.wwwrs.co.nz - seems to always return "not found" for me!
They will mail though!

RS pages
Easyradio
Book
 

Jethro

New Member
The NZ page did not load. :( Sent an email to EasyRadio USA, but I think its gonna cost over the top to get anything shipped to New Zealand. The ER400TRS looked very good though.

I'm not to fixed on any particular frequency at this point, in fact I would have though higher frequencies to be more efficient. It just so happens that CB's are available for use without a lisence in NZ and transmission on this frequency may be more legal. (Hold on... don't most garage door openers operate at 433Mhz?? Hell)
 
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