4 ms·

The article states they used a small antenna to detect the satellite signals but how small is small? After all, the SpaceX "Dishy" is fairly large, heavy and po

by spuz 5y ago

The article states they used a small antenna to detect the satellite signals but how small is small? After all, the SpaceX "Dishy" is fairly large, heavy and power hungry. Would this technique really be possible with an antenna small enough to strap around the neck of an animal? What about something that could fit in my phone?

ta988 5y ago
You don't need to emit (that uses a lot of power) so that's already one factor.
piannucci 5y ago
Their antenna was a CotS LNBF. Think just the bit on the end of the arm of a DirecTV dish, not the dish itself. Typical aperture maybe 10cm, full unit about hand-sized.
vel0city 5y ago
"Dishy" size is because its a two-dimensional phased-array antenna. It has a lot of small antennas on it to steer the energy released from the antenna directionally through interference patterns. If you're only going to receive and the signals are powerful enough you don't need that big of an antenna to receive signals at these frequencies.
stephen_g 5y ago
You can do satellite comms on something that small (maybe an antenna a few centimetres square) if you're only interested in moving a few bits per second or maybe kilobits per second. In the transmit direction you're generally limited by how much power you can pump out (the smaller the antenna, the less antenna gain you have and the more power you need to produce from your transmit chain). In the receive direction, you have a figure called G/T which has to do with the ratio of the antenna gain to the noise temperature of the receiver chain (which includes thermal noise picked up to the universe, plus noise introduced at each gain stage etc.). The simpler the modulation, the less power you need generally, but you can move less data in a given amount of frequency spectrum, so that's the tradeoff.

4 ms·

The article states they used a small antenna to detect the satellite signals but how small is small? After all, the SpaceX "Dishy" is fairly large, heavy and po

by spuz 5y ago

ta988 5y ago
You don't need to emit (that uses a lot of power) so that's already one factor.
piannucci 5y ago
Their antenna was a CotS LNBF. Think just the bit on the end of the arm of a DirecTV dish, not the dish itself. Typical aperture maybe 10cm, full unit about hand-sized.
vel0city 5y ago
"Dishy" size is because its a two-dimensional phased-array antenna. It has a lot of small antennas on it to steer the energy released from the antenna directionally through interference patterns. If you're only going to receive and the signals are powerful enough you don't need that big of an antenna to receive signals at these frequencies.
stephen_g 5y ago
You can do satellite comms on something that small (maybe an antenna a few centimetres square) if you're only interested in moving a few bits per second or maybe kilobits per second. In the transmit direction you're generally limited by how much power you can pump out (the smaller the antenna, the less antenna gain you have and the more power you need to produce from your transmit chain). In the receive direction, you have a figure called G/T which has to do with the ratio of the antenna gain to the noise temperature of the receiver chain (which includes thermal noise picked up to the universe, plus noise introduced at each gain stage etc.). The simpler the modulation, the less power you need generally, but you can move less data in a given amount of frequency spectrum, so that's the tradeoff.