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Two classic and highly effective fractal antennas are the log periodic antenna and the many variations (planar, conical, cylindrical, etc.) of the log spiral antenna. The main characteristic of both of these antenna families is extremely broad bandwidth, which can be attributed to the fractal self similarity at multiple scales. Most other fractal antennas ...


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To complement Brian K1LI and his Fractal antenna, I thought I would give you another design which is more space-filling, and may yield better results for you. (see graphic at bottom). Their application is antennas for cars. You can see how their space-filling-fractals (the squares/diamonds) are electrically much longer, and therefore fit into smaller spaces (...


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One of the comments for this question includes a link to a paper on blast-resistant ground level HF antenna's that the U.S. Airforce used or uses. So zero. Or negative if you count the buried cavity.


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$Z_{fs}$ (space) is resonant at all frequencies due to $\varepsilon_0$ (farads/meter) and $\mu_0$ (henries/meter). Thus it will have no reflection. Free space is lossless and the signal only gets weaker because the energy spreads out over a larger and larger sphere. The /meter part causes space to develop a resonant velocity (speed of light). But all ...


1

The likelihood of an antenna interfering with another antenna diminishes as their respective frequencies get further apart. Typically, if they are on different non-harmonic bands, it won't be an issue, and if they are harmonic, the higher frequency antenna might cause interference on the lower frequency antenna, not the reverse. Dishes are probably above ...


3

Minimum height to accomplish what? It'll work right down to the ground, it'll just get lossier and lossier the lower you hang it. The exact numbers depend on your ground, and the threshold of "good enough" depends on you, your power, and who you're trying to talk to, so there's no real hard limit. Some unsourced internet numbers suggest that at 0....


2

Of course there can be interference but I would guesstimate the probability at about 30%, so that 70% chance that there will be no interference - basically have to try to find out. If there is interference you can move the antenna a little bit and that might even fix it or install a filter that might fix it, or use less power on certain frequencies. I would ...


3

As already mentioned by @Andrew's answer; as a general rule: the higher the better. Another very important rule is: any antenna is better than no antenna. So a hex-beam on top of a 24 floor building is better than none ! Lightning was mentioned, which is something you need to give serious thought. Try to find out who is the facilities engineer, and have a ...


3

The general rule of thumb is that for antennas the higher the better. The height above ground in this case is an absolute advantage. Your ability to put an antenna on top of a very high building is enviable to say the least. Height above ground affects the angle of radiation, which is the vertical angle compared to ground of maximum radiation for an antenna. ...


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