From the calculations and theory displayed in the above sections, it can be seen that a communications link can successfully transmit data from falling probes to a relay satellite and from the relay satellite to the Earth. The ability to focus and point a dish antenna towards a specific target is what makes deep-space communications successful. For example, without the gain of the transmitting and receiving Deep Space Network antenna, the carrier to noise ratio at the receiver would be -138 dB!
This shows how important dish antennas are; the 34-meter dishes at NASA's Deep Space Network provide enough gain such that even low-powered signals traveling from billions of kilometers away can still be received with a low probability of error.
The most important stage of the communications link was the low noise amplifier on the relay satellite. This amplifier was able to amplify the incoming signal from the probe and increase the carrier power to a level that could be used for demodulation. Spread spectrum also played an important role in providing processing gain to the signal, whose noise level was actually greater than that of the carrier.
The most challenging part of this project was obtaining real parts and using their specifications to determine the outcome of the link budgets. Many of the parts did not specify a noise directly in terms of °K, nor did the dish antennas provide a gain rating and efficiency at the desired frequency. All of these ratings had to be put into units that were familiar with what was learned during the semester so that they could be used in the appropriate calculations.
All of the calculations for this project were done in Mathematica. This notebook can be downloaded here.
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