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Radio Frequency question

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ssembo

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1. A deep space communication system uses a Cassegrain antenna of diameter 70m at a frequency of 8.45 GHz.
i) Determine the gain of this dish (in dBi) assuming an aperture efficiency of 80%
ii) Determine the power received by this dish from a transmission from a satellite having antenna gain 2.2 dBi and transmitter power of 10 W at a distance of 180 million kilometers.

2. i) A transmitting antenna that radiates a power of 11Watts, has gain of 3 dBi and efficiency 0f 90%. Calculate the required gain and effective aperture of the receiving antenna at a distance of 8 km operating at 7Ghz. The expected power at the receiver antenna should be 2 watts.
ii) Calculate its Effective Isotropic radiated power.
 
What have you learned in class the might help you answer those questions.
 
What have you learned in class the might help you answer those questions.

the lack of a response infers .... obviously not enough ;)

in reference to Q2 he isnt going to get 2W at the receiving antenna at any distance greater than ~ 1 metre anyway cuz of the inverse square law. And the size of the receiving antenna isnt going to make much difference, its still going to be in the very low microWatt range.

Doing some basic pathloss calcs..... with his 11W ERP and a 7GHz, 8km LOS pathloss of 127.5dB. Signal level @ the receiving antenna (excluding any RX Antenna gain) will be -87dBm (+ - a dB or 2).
I dont see him building a > 150dB receiving antenna for 7GHz any time soon to try and realise 2W of power out of the antenna.

Really the Q is poorely worded. He's already given the ERP of the antenna of 11W and an antenna gain of 3dBi with a 90% efficiency. So the actual transmitter power arriving at the antenna is only ~ 6W (give or take a Watt)
He's then saying 2Watts at the receiving antenna rather than probably meaning 2W after the gain of the receiving antenna is taken into account.

anyway, without an impossibly huge receiving dish antenna, it isnt going to happen... well not in real life anyway, tho anything is possible on paper ;)

cheers
Dave
 
anyway, without an impossibly huge receiving dish antenna, it isnt going to happen... well not in real life anyway, tho anything is possible on paper ;)

I really hate it when students post entire homework/tutorial questions on this forum and expect other to give them the complete answer, which they can perhaps copy and submit? Especially when the solutions to the questions are possible on paper only and impractical otherwise. This remind me of my university days when the solution to one of the 555 timer tutorials was to use a 8Mohm resistor to create the expected frequency. I bet anyone can find such a high value resistor easily (Years later I did manage to find one in my CRT monitor).
 
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