Originally posted by KazetNagorra
[b]No idea, I'm a theorist, and an undergraduate at that.[/b
So do you know yet how to calc the Q of a superconducting dipole antenna?
A dipole antenna is a half-wavelength long, so at 40 meters, one of our hambands, you divide the frequency, 40 meters~=7 Mhz, so to find the length of the dipole, which is two equal length 1/4 wavelength sections stretched out with the feedline in the center, so divide the magic # (468) by the frequency in Mhz, and you get the length of the dipole, just shy of 67 feet, or a bit over 33 feet for each 1/4 wave sections. Using those #'s, and the antenna wire diameter, I think, the Q can be figured out, that is to say a center frequency of say, exactly 7 Mhz and then the chart of how the response of the antenna drops off when you go to say, 7.1, 7.2, 7.3, 7.4, 7.5 Mhz, etc., so you build up an SWR chart (standing wave ratio) which when matched perfectly, say a feedline impedence of 73 ohms, a typical dipole impedence, and it's matched to a transmitter also at 73 ohms, then the SWR is 1:1 exactly, so 100 watts fed to the antenna means 100 watts leaves the antenna and nothing heads back to the transmitter. If it were say, 36 ohms instead, 100 watts would head out to the antenna but about half of it would shoot right back to the transmitter, causing no end of trouble there, transmitters like to be one way
, they don't like reflected energy zapping them. However, if a transmitter was nearby, transmitting on say, 7.1 Mhz, it would pile up a lot of energy into a receiver tuned to 7.0 Mhz, which would ordinarily be rejected by a series of filters either analog or digital in nature. That works ok, but if the antenna itself can reject frequencies near the operating frequency, the resulting signal to noise ratio will be better, less noise, more signal because off frequency signals will be rejected by the antenna before the operating frequency ever reaches the receiver, see what I mean? That's why I want to explore the Q of a superconductor antenna. Any Idea of how to go about doing the math for this? If you use the standard math, the Q would be infinite, which wouldn't be happening in THIS universe
, if that were really true, it would be good for say, 7,000,000.000 Hertz but not good for 7,000,000.001 Hertz! That would be such a narrow bandwidth as to be useless for vocal communications which takes at least 2,000 Hz of analog bandwidth to transmit. So the Q # is a very important value to consider. Any help with that would be appreciated.