RF Satellite/Base station Link Budge analysis

Discussion in 'Wireless & RF Design' started by Mark Stanners, Feb 22, 2017.

  1. Mark Stanners

    Thread Starter New Member

    Feb 22, 2017
    1
    0
    I have an assignment as part of my uni course which I am struggling with. It is based on RF design and so I am hoping somebody here could help me out. I have searched the forum but nothing really pops up
    I have been tasked with completing a link budget analysis for a rf channel between a satellite and a base station at my university.
    My problem is that I have done countless hours of research, but must be looking in all the wrong places. I have calculated, using matlab a SNR at the different heights but to fully analyse a link budget do I need to know the minimum SNR, to find the CNR and budget margin?


    Channel frequency- it is transmitting in C band and so I have quite a few MHz for my channel. I have researched spare frequencies but have no idea how I can choose my bandwidth for C band (I was going to use 4-4.2 MHz) are there legal implications or can you just jump on a channel?

    Also appropriate antennas- how do you decide what type antenna is appropriate? are there specific ones for C band. I know that antenna length ties in to signal length but satellites and base stations are a bit beyond me.

    What I was hoping for any help that you RF fans could provide, if its books, websites or just knowledge that you have it would be greatly appreciated.

    Thanks,

    Mark

    Communication Channel Design Parameters:

    The following parameters should be utilised for the communication channel design.

    Category of satellite: Microsatellite;
    Calculated core bus power: 60 W
    Allocated communication subsystem percentage for a communication mission (for uplink and downlink data transmission) (%): 19.
    Altitude of satellite (km): 700 to 800;
    Elevation angle of the satellite(o): 0 to 180
    Earth’s radius (km): 6371;
    Speed of light (km/s): 300,000;
    Available frequencies for uplink and downlink transmissions (GHz): 4 and 6;
    Omnidirectional antennas with gains of 0 dBi are installed; and
    Noise floor (dBm): -90.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    4,166
    1,125
    For satellite comms you will use a dish. The freq band requirement is not so stringent, but they WILL become very upset if you start spraying C Band RF all across the northern hemisphere night sky.

    You will need to find the satellite with a received signal and then transmit to the same location while tracking the trajectory.

    The RF portion is easy, the tracking and aiming part will be the expensive headache.

    Geosynchronous is the easy method, moving targets take more technology to support the communication part.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    11,708
    2,465
    You probably can't just find a channel and jump on. With respect to Amateur Radio Operations here's what the wiki says:

    The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range 5.650 to 5.925 GHz, and amateur satellite operations are allowed in the ranges 5.830 to 5.850 GHz for down-links and 5.650 to 5.670 GHz for up-links.

    As has already been mentioned if you step on somebody's operation you'll probably hear about it from the G-men.
    The good news is that since dish antennas are highly directional, your chances of interfering with other operators is smaller than with other antenna types.

    Check the following article
    https://en.wikipedia.org/wiki/Minimum_detectable_signal
    Check out the link to the PDF file in the references.

    On 10M(28 MHz.) and 6M(50 MHz.), it is not uncommon to detect SSB signals peaking at -110 dBm, with the noise floor at about -120 dBm.
     
    Last edited: Feb 22, 2017
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