I think that it's been perfectly stated that satellites need 1,5-2kW of energy, not less, not more. I don't know what's there to discuss about, the 50kW is definitely made up out of thin air.
lol, a heater has that power, and you think it is enough to send signal to cover a very large zone of land? that's a joke
Jeff
So you are now the local expert on radio propagation. Now I won't pretend to have all the answers here off pat because antenna design, signal propagation, atmospheric attenuation are very large topics and fill books, but there are a few points you might want to look into.
I cannot put this too simply or it would be meaningless, but I will try to be brief.
The big problem is that you can ridicule a topic from pure ignorance, but to answer that ridicule is not so easy.
Now, I don't know whether your 50 kW figure is for an FM radio or digital TV, so I will assume it is DTV.
For both satellite TV and terrestrial TV, the signal needed from the transmitter depends on:
- Transmitting antenna gain,
- Path attenuation,
- Receiving antenna gain and
- Receiver sensitivity.
Terrestrial TVTerrestrial TV uses frequencies in the few hundred up a bit over 800 MHz range.
- Transmitting antenna gain
The transmitting antenna only has to cover the one band, but usually cannot be directional as it must broadcast to receivers all around it, so a high gain cannot be achieved. For the moments I will take the effective gain as about 3 dB - a guess!
Lots to read in Alan Dick, AN INTRODUCTION TO BROADCAST TRANSMITTING ANTENNAS.
- Path attenuation
I do not have quick figures here, but the signal has to traverse many kilometers of the lower atmosphere, and at the longer distance cope with obstruction from intervening hills, etc.
- Receiving antenna gain
Because such a wide range has to be covered, very high gain antennas are cumbersome and very expensive.
As a result most terrestrial TV receiving antennae have a gain of
less than 6 dB.
- DTV receiver Sensitivity
A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm
From: ATSC Recommended Practice:
Receiver Performance Guidelines.
While this is recommended, many Digital TVs require a much higher signal level of -68 dBm.
Now satellite TV is quite different. The wavelengths are much shorter making high gain directional antennae quite practical.
- Transmitting antenna
This antenna can limit its coverage to a comparatively narrow beam. This depends on the coverage required, but might typically be about 5,000 km in circumference. This corresponds to a beam width os roughly 8°. As a result, the gain of the satellite's transmitting can be much higher than for a terrestrial TV broadcasting antenna.
A rough calculation (and I stand to be corrected) of the gain of this antenna would be about 20 dB.
- Path attenuation
The satellite signal might have to traverse up to 40,000 km, but apart from the spreading beam (the inverse square law), then the signal traverses an effective 10 to There in no path attenuation to contend with in the free space, only in the relative short atmospheric path.
- Receiving antenna gain
This is where the biggest gain comes in. Because of the short wavelength, quite small dishes can give a very high gain. A 60 cm dish usuall has a gain of about 30 dB.
- Receiver sensitivity
A satellite TV receiver typically has a Low Noise Amplifier (LNA) right on the dish, so a better receiver sensitivity can be achieved for terrestrial TV, commonly about a 10 dB improvement.
I have hurried through this, but summarising I will table the improvement in the satellite system as opposed to the terrestrial:
- Transmitting antenna gain: 20 dB vs. 3 dB or 17 dB in favour of satellite,
- Path attenuation: bit of a guess, assume they are not much different overall.
- Receiving antenna gain: 30 dB vs. 6 dB or 24 dB in favour of satellite.
- Receiver sensitivity -80 dBm vs. -68 dBm or 12 dB in favour of satellite.
Overall this gives the satellite link up to a 53 dB advantage over the terrestrial link, mainly from the narrower beam antennae that can be used.
This is a power ratio of almost 200,000, some of which lets a lower transmitter be used, some of which is need for the wider area covered.
But the "power budget" of a TV satellite it is definitely quite possible.Must go now, I'll come back later and patch the numerous errors.