There are ways of sending e-mail via APRS/packet data over VHF and HF frequencies through amateur radio. There are a few issues which you face such as the fact that broadcasting is not allowed under amateur radio licenced conditions. That rules out the broadcast to many aspect. However, you could always devise a method of requesting pages from a server which then transmit that as a data packet over RF. Throw in an identifier to show what was requested and you become compliant. APRS is worth investigating as it is a network of data which interfaces to the internet. The speed of transmission which can be achieved over these frequencies is not great. There is a reason that companies such as Alphabet are trying to use light as a transmission medium over RF for crossing rivers in the Congo. Though, smolnet is nice and efficient in use of memory so that may not be a concern and any smolnet access is better than none. Propagation can be an issue for the HF bands in particular with it fluctuating wildly as the Earth spins. I would be tempted to use NVIS to ensure consistant propagation over a 400 km or so radius. Although the working frequency will change as the planet rotates so you still do not get something constant enough. Perhaps VHF is the best way. Ranges should be up to 50ish km with a half decent antenna and an efficiently encoded data signal with nice bit error recovery schemes designed in.
Thank you for this valuable insight! =)
I have not worked with amateur radio in any way, so there are a few acronyms here to research first. (I have a background in electronics and did some research on radio-frequency transmission, but I moved to servers and Internet pretty soon)
I recalled hearing in a podcast about a similar use case with AM radio waves used to transmit data from humidity sensors in farmlands. As you say, it was extremely slow but reliable enough.
Pages I should read later: