Any suggestions or recommendations for transmitting data 5km to 10km ?

The transmitting unit has these requirements -

 - No bigger than 100mm x 100mm x 20mm (100 x 50 x 20 prefered)
- Battery-powered for up to 2 years (if possible, solar an option)
- Data transmission probably a dozen bytes every 5 minutes
- Aerial acceptable only if short, stubby, robust etc
- Receive capability not needed

There are no telecoms (such as cellular or paging) guaranteed
to be available, in all likelihood this needs to be achievable in
remote areas

Apart from the tx, everything else is pretty much sorted. A couple of
days ago someone mentioned the 340 as a better choice for a very
low-power sleeping micro. Is that true it's better than the PIC ?

TIA

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