Interesting stuff, I work with RF and I was curious how a passive component can have such a high gain (given that gain is usually measured as an increase in energy of a signal).
Turns out the way that the gain of a passive reflector seems to be measured is: "the ratio of the power density at a distant point due to the passive repeater to the power density which would exist at the same point" if the repeater were replaced by a matched antenna (or basically nothing at all).
So basically it's a measure of how much better the signal is when you add the reflector, and that's why it can achieve such high gains: because the signals traveling so far are already being atmospherically attenuated by hundreds of dB. Maybe that's not new information to others.
Anyways, cool stuff. Sometimes the best solutions are the simplest.
Still used nowadays: airplane reflections are being used by ham radio dudes. There's a software around that even calculates the optimal reflection parameters based on ADS-B aggregators.
Thanks too relatively modern digital modes this doesn't need too much transmission power.
On the upper GHz bands with dishes they even manage to do reliable FM chats. But that requires a lot of gain and active steering of the dish.
One scenario would be if it scanned it once in 8 days and once in 4 days, due to, say, an elliptical orbit or something. Thus, twice in 12 days, but not once every 6 days.
Alternately, complex orbital tracks may result in irregular accumulation of multiple scans, with double scanning only finally being achieved after 12 days.
Interesting stuff, I work with RF and I was curious how a passive component can have such a high gain (given that gain is usually measured as an increase in energy of a signal).
Turns out the way that the gain of a passive reflector seems to be measured is: "the ratio of the power density at a distant point due to the passive repeater to the power density which would exist at the same point" if the repeater were replaced by a matched antenna (or basically nothing at all).
So basically it's a measure of how much better the signal is when you add the reflector, and that's why it can achieve such high gains: because the signals traveling so far are already being atmospherically attenuated by hundreds of dB. Maybe that's not new information to others.
Anyways, cool stuff. Sometimes the best solutions are the simplest.
http://www.gbppr.net/splat/Passive-Repeater-Engineering.pdf#...
Yes, this is what makes moon bounce (EME) attainable. The gain of the moon is about 142 dB at 1296 MHz.
Still used nowadays: airplane reflections are being used by ham radio dudes. There's a software around that even calculates the optimal reflection parameters based on ADS-B aggregators.
Thanks too relatively modern digital modes this doesn't need too much transmission power.
On the upper GHz bands with dishes they even manage to do reliable FM chats. But that requires a lot of gain and active steering of the dish.
Also briefly attempted in space in the 1960's,
https://en.wikipedia.org/wiki/Project_Echo
Radio astronomy was an accidental offshoot of this project: they noticed the reflected microwave signals from space came back with some extra noise...
Very topical item, with NISAR unfurling to it's full 39 foot deployment up in space.
https://www.jpl.nasa.gov/news/giant-radar-antenna-reflector-...
“The mission scans nearly all the planet’s land and ice surfaces twice every 12 days.” What was wrong with saying once every 6 days?
One scenario would be if it scanned it once in 8 days and once in 4 days, due to, say, an elliptical orbit or something. Thus, twice in 12 days, but not once every 6 days.
Alternately, complex orbital tracks may result in irregular accumulation of multiple scans, with double scanning only finally being achieved after 12 days.
Whoa incredible! Can you believe it does four scans every 24 days?!