Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx> At 12:29 PM 4/8/2006, Tesla list wrote:
Original poster: gary350@xxxxxxxxxxxxxI have an idea. A transmitter antenna radiates output power just like the topload of the tesla coil radiates sparks.Does the physical size of an antenna increase or decrease the output power?
Neither. There's a tradeoff between size, gain, bandwidth, and efficiency. A small antenna, if efficient, will tend to to be narrow band.
I know an antenna needs to be tuned to the circuit. A multi element beam antenna for example, 2 element beam compaired to a 4 element beam. Next a 4 element beam antenna compaired to an 8 element beam antenna. The 8 element is physically larger than a 4 element and it is larger than a 2 element. Reception and power output are both better with the physically larger antenna.
The "gain" of the anntenna is higher with the bigger antennas, but the actual power radiated is still the same. It's just squirted in a smaller range of directions. On receive, there is a physical size impact, particularly for antennas very much larger than a wavelength. For small antennas, the effective aperture is more driven by the size of the reactive near field, rather than the physical size of the antenna.
My next thought is, an amateur radio antenna like 80 meters, 40 meters, 20 meters, 2 meters do not physically radiate visible discharge sparks like a Tesla coil. WHY?
Sparks are mostly a matter of what the electric field is. In a typical amateur radio antenna, the electric field at the ends of the dipole aren't high enough to spark. However, run a lot of power through a short antenna, and you'll get breakdown at the ends. I've seen corona discharge off the end of a short 40meter vertical with a kilowatt going to it.
If the amateur radio antenna were to be retuned would it radiate sparks that could be seen just like a tesla coil? If so then would it still transmit a signal several 100 miles to a receiver? If a tesla coil topload were to be retuned would it transmit just like an amature radio antenna?
Here, you're back to the tradeoff between physical size, efficiency, etc. A physically small antenna (in terms of wavelength) will tend to be less efficient *as a radiator* than a physically large.