Pice
TAPR.org has some pretty intense kits for transmitting data over packet radio, you could use one of their kits with a PIC microcontroller to take serial data from a GPS receiver or weather station and transmit it as formatted packet frames… Here’s a bit about the organization and the kit store page…

“If you have used a packet radio TNC, then you are already a part of TAPR history. The TNC (Terminal Node Controller) project grew from a discussion in October of 1981 at a meeting of the Tucson Chapter of the IEEE Computer Society. A week later, six of the attendees gathered and discussed the feasibility of developing a Terminal Node Controller that would be complete and available to amateurs at a modest cost. This was the genesis of TAPR. On June 26th 1982, Lyle Johnson, WA7GXD, and Den Connors, KD2S, initiated a packet contact with the first TAPR unit. The project progressed from these first prototype units to the TNC-1 and then finally to the TNC-2 which is now the basis for most amateur packet operations worldwide. TAPR was founded in 1982 as a international organization with interests in the areas of packet and digital communications. Today, TAPR continues as a membership supported non-profit amateur research and development organization. TAPR currently has more than 2000 members, worldwide and continues to develop kits for the amateur community and is working actively on publications and communications standards. TAPR is the place for digital communication information and research.”Link.