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I'm starting to study RF propagation at college, and I'm thinking about what antenna I should choose for this scenario:

enter image description here

The distance between the transmitter and receiver is just 700 meters, and the link is not line-of-sight because there are 2 buildings in the way.

The frequency is 408.00625 Mhz and the bandwidth will be 12.5 Khz FM.

Do you think a 1/2 wavelength dipole (omnidirectional) will work for this? Or would a Yagi (directional) be better? I think that a Yagi would oversize the link[?].

Which one of these antennas would be the best choice?

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A complete analysis of this situation first must consider the propagation path performance, and then the types(s) of antennas to use w.r.t. the losses on that path. This short propagation path has nearly a fixed propagation loss regardless of the antennas/patterns in use.

Antenna characteristics depend on path losses, the Z-matched power at the tx antenna input, tx antenna gain toward the rx antenna, rx antenna gain toward the tx antenna, the r-f signal needed at the receiver input connector for acceptable performance of the overall link system (including fade margin), and signal reflections from other structures and surfaces in the propagation environment.

Below is a graphic showing general considerations for point-point link paths.

enter image description here

Richard Fry
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What you need is a link budget. A higher gain antenna (such as a Yagi) adds gain to your budget and makes the link more likely to work, or allows for less transmit power.

I'm not sure what you mean by "oversizing" a link. Using an antenna with more gain than necessary has no particular disadvantage other than the antenna might be larger or more expensive than necessary.

With buildings blocking line of sight like that, you might be better off looking for a repeater or passive reflector.

Phil Frost - W8II
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Taking this as a theoretical question, and not knowing anything else such as how the buildings are oriented, what they are made of, or how much power you are using, I will step out and say that in general you will get maximum signal from A to B by using a pair of Yagi-Uda antennas.

The trick, due to scattering, or knife-edge effects, plus the fact that building faces tend to change the polarity of reflections, will be the orientation of the respective antennas.

That answers your question as asked.

To get a more precise answer would require more information.

SDsolar
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