User talk:Average/Radio Enthusiasts
beginning of update v3.1
Revolution UPDATE v3.0. This page has being updated again for transmission power limits. Use the more conservative power guidelines until updatev3.1. Any questions, find Capt. Dynamite.
Of course, we need cheap, two-way, metro-distance for mesh networking and cheap one-way, long-distance communication for broadcasting the revolution.
Ham radio, adhoc/mesh (more-or-less flat, multi-hop, spontaneous) networking (B.A.T.M.A.N, ZigBee), municipal wifi: these are tools for freedom-lovers everywhere.
Need clandestine, two way communications? No problem, spark generated with the right conductor plate should be tunable to send binary yes and no signals back to your central hub. Shannon's information theory tells us that we can send low-bit information readily across an extremely low-bandwidth channel. Perhaps sparking that gap at a predetermined cadence to communicate that it isn't a random noise.
Otherwise, it should create no problem to broadcast a low-power, or less than 50Watts2/1-mile-diameter-circle radio station on some unused, unlicensed frequency (that means 10 devices of 5W each or 1 device at 50W) that conforms to the interval tolerances of the FCC (say 0.2% --does that leave any band?) and the tuning accuracy must be tight enough not to wander out of these tolerances. That means on any arbitrary 1-mile circle, your total wattage is <50W, like a heat map that must stay below a certain temperature. You won't get protection from the FCC if someone jams your transmission, but hey just invite the jammers over!
So for mesh networking, you have to add up the total number of transmitters and their power in any given mile-circle and keep it under the 50W limit. This should be acceptible to everyone, including the bureaucrats at the FCC. I base this on citizen radio history, research on existing power usage on various devices, amateur radio, and interactions with the powers-at-large.
Radio transmissions happen in the imaginary, or i, dimension. That is a space of non-reality. Watt2 means two such dimensions, i and j. Your antenna catches these imaginary dimensional emissions and your electronics transduces them into your positive dimension as an audio signal. Fractal antennae may worth experimenting with as well as spherical resonant chambers, each tuned (built around) to a desired wavelength.
Put a light on top of your antenna whenever you switch the transmitter on to let the community know when you're making things happen!
In short, for municipal-range radio:
- 2 mile transmission range limit from unlicensed operators (as measured by average, single-axis) one-way transmission. Consider this the safe distance limit for reception. But using a lesser-used CB frequency could be legally defensable. "Range" here means you shouldn't be able to tune in on an unspecialized antenna at said distance.
- Frequency suggestions: CB CH1, I hear, can be set aside for datacomm. Old UHF bands are also a good bet (channels 32-34, (477.2000-477.2500MHz) are supposedly set aside). Try those first. Stay away from 2-way radio bands and any emergency bands.
- 50W2/1mile-diameter-circle total radiation (unused wavelenths, of course), perhaps less around populated centers where you might expect radio reception to be commonly used. This is not a suggested power: you must attenuate your transmitter until you get under the range requirement. Different ambient radio environments make different challenges, but the first requirement nails down your limit.
- don't broadcast on any licensed spectra, and for the sake of the community, consider any other unknown transmission as possibly licensed and legit, until deduced or shown otherwise. If you are a licensed operator, as a courtesy, you can place your call-sign encoded in each packet at the lowest layer you have available (as aribtrary data).
- mobile (actually in-motion) use can be an issue if you are using homemade transmitters. GPS is favored here, so you might be trampling on that, except for very low-power tranmissions (under a watt). So keep that in mind.
Another option for coffee-shop-range radio:
- 100ft range limit
- 4.7W2 /50ft-diameter-circle max power, again attenuate to satisfy first limit
- R/C bands may be best here (which have up to 25W unlicensed watts, btw, far more than this ~5W limit).
Basically, the formula for any given power band for unlicensed 2-way radio, using standard (but tuned to wavelength) antenna is:
- Xmitter-Watts2/2*radius < 0.25Watts2/ft.
- max reception distance < 4*radius (above radius)
- take out the factor 2 in your divisor if it's one-way radio (since you're using 1/2 the power in the given range).
If you think about it, 0.5watts2/ft is extremely gentle requirement, yet also tunable. This formula allows you to figure out your power no matter how much the distance you want to transmit.
Exercise #1: You want a 1-way radio able to broadcast to 30 miles.
- Feet = x2, x is your unknown transmitter power
- x = sqrt(5280*30), re-arranging terms
- x must be less than 398 Watts and attenuated until untunable at 60mi on your free-est path. This part is necessary to make the bureaucrats feel safe.
Exercise #2: You want a single 2-way conversation around the globe with a licensed radio operator operating at 5000W:
- total power < sqrt(5280*12500)
- 8124 W total energy, subtract your conversant's 5000W
- 3124W of MAX power. XXX see note below..
That's a large amount of unlicensed output, so keep the reception limit to 2 miles (and 50W2) until futher testing.
