Post disaster Prime Base Comminications

[cosmicfish]

Originally Posted by tsofian

Wikipedia has this to say about ULF range Radio amateurs and electronics hobbyists have used this mode for limited range communications using audio power amplifiers connected to widely spaced electrode pairs hammered into the soil. At the receiving end, the signal is detected as a weak electric current between a further pair of electrodes. Using weak signal reception methods with PC-based DSP filtering with extremely narrow bandwidths, it is possible to receive signals at a range of a few kilometers with a transmitting power of 10-100 W and electrode spacing of around 10–50 m.

You are acommo guy so probably have more information to share

Transmitting through bedrock has significant problems over long range, and there are lots of ways to transmit securely, especially in a post-war, resource starved environment. There are a few ways that shouldn't be discussed on here, but one simple way going back to your directional antenna idea is to use a single tight-beam link (laser, perhaps) to transmit to an in-range relay station with a command to rebroadcast isotropic. It is unlikely that the tight-beam is intercepted or blocked in time to stop the transmission, and if they find the relay station, so what? Losing that is well worth transmitting the codes.