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### Can there be (long range) propagation of HF from satellites?

HF transmissions from the ground can be reflected by the ionosphere leading to very long distance propagation. Satellites in low Earth orbit (160 km to 2,000 km) fly within the ionosphere (60 km to ...
7k views

### Why is antenna aperture a function of wavelength?

Wikipedia says: It can be shown that the aperture of a lossless isotropic antenna, which by definition has unity gain, is: $$A_{\mathit{eff}} = \frac {\lambda^2}{4 \pi}$$ We also see this emerge as ...
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### World wide Radio Module

currently I am involved in a project were a data link is needed to communicate different devices. This is in one to many configuration and the devices are stand alone. For this project there is need ...
14k views

### What is the aperture efficiency of an antenna?

For reflector antennas, I see a number called aperture efficiency. What does it mean?
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### Why does path loss decrease as frequency decreases? [duplicate]

The Friis transmission equation can be given as: Pr = Pt + Gt + Gr + 20 log10 (λ / 4πR) Where the variables represent: ...
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### Why is VHF better than UHF in this situation?

One of the sample questions for the British foundation level test is: An amateur has the choice of VHF or UHF for a particular contact of some 25km. Which statement below best describes his choice? ...
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### Can sub GHZ frequency can be used in space communciation?

Is it possible for a sub GHZ frequency (Say 300 Mhz) can be used for space communication for small satellites such as a cubesat? What are the advantages and disadvantages for this.
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### Can we transfer digital files on radio spectrum?

Radio is analog, and a modem converts analog signals to digital signals and vice versa. So is P2P sharing of digital files (like .exe, .7z, .pdf or any other file) possible using radio spectrum? ...
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### Range of wireless signals

I've put up this question already on physics.SE but I miss an answer to the following: My assumption: A 5 GHz band provides a higher bandwidth and therefore is more stable as it can support more ...
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### Is 2.4Ghz good for an UAV?

I'm designing a drone(UAV) as a hobbyist, and radio communications is not my strong point. I will be transmitting waypoints from a portable control station and receiving video(a low frame rate is ok). ...