Having pondered it some more, for my campaign (a 'classic' period setting) I'll probably go with this:
Quote:
In the wake of World War III, landlines would be cut, microwave links destroyed by EMP, and many satellites shot down or left to spiral down into the atmosphere. The Project wasn't nearly about to launch its own set of communications satellites covertly (one way to inadvertently cause World War III, at least!). There was some uncertainty about the effectiveness of long-distance radio transmission in the wake of a nuclear war, but in the end the Project decided to stick with radio transmission.
Team activation signals, and low-rate strategic messaging, are sent on VLF frequencies. Transmitting antennae for this system are very large -- kilometers across for a trans-continental system -- and transmission is very inefficient; power requirements are in the hundreds of kilowatts, or even several megawatts. However, receiving antenna are simple coils, as small as 10 cm in diameter; and the receiving radios in boltholes are an unimpressive piece of rack-mounted equipment (including decryption equipment).
The actual coil antenna used for Project boltholes is about 30 centimeters in diameter, wound with more than a thousand loops of insulated wire (so: more than a kilometer of wire). Note that the antenna design doesn't tell you much about the frequencies being received, except that it's VLF. It's placed just at the surface for most boltholes, mounted on a sturdy pillar anchored in the bolthole structure. An artificial rock of thick, fiber-reinforced polyimide resin is also mounted on the pillar, and encases the antenna; it's very strong, chemically resistant, and fireproof up to at least 800° F (1300° F for brief periods). The artificial rock also means the team probably won't be able to get at the antenna wire.
The transmission rate, using FSK modulation, is about 5 characters per second (using ASCII 8-bit characters). Encryption padding and other "non-text" parts of messages roughly double the transmitted wakeup signal. A wakeup signal might be 300 characters of useful information -- 600 characters as transmitted in encrypted format: thus 2 minutes to transmit.
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A game-play/dramatic advantage for this: the transmitters are huge and need a lot of power; but receivers can be trivially small. So the typical player-character Recon team can receive their instructions, but can't chitter-chatter back and forth with Damocles or whomever.
The 300 character size for the wakeup signal is based on the one at page 7 of
Operation Lucifer.
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Michael B.