eli5: NASA mostly uses UHF antennas for interspace communication, why?
In: Physics
You are off by about an order of magnitude as most communications is in the SHF range. Just looking at the current Deep Space Network data and all of its links are in the 7-8GHz range while UHF is only between 300MHz to 3GHz. The reason for these high frequencies is because of the small size of the equipment and the large bandwidth it is capable of. Radio equipment is generally pretty similar and have roughly the same size measured in wavelength and roughly the same bandwidth measured in percentage of carrier frequency. This means that by increasing the frequency you are also reducing the size of the components including the antenna and also increasing the bandwidth. The bandwidth is important not necessarily in order to transfer data faster but it allows you to add error correcting code which allows you to correct any errors in the data stream which again means you can reduce transmission power. The reason they are not using even higher frequencies is that the atmosphere is absorbing much more of these high frequencies. And while there is not much atmosphere between a ground based antenna and a space probe it is still significant enough to matter quite a bit. NASA is actually testing out communications over frequencies that is even higher where the atmosphere lets it through again. And although we have used it to test communication with some space probes the technology still have some way to go before it can be used reliably.
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