Australian CubeSat to use 76 GHz

Discussion in 'Amateur Radio News' started by G4TUT, Apr 13, 2019.

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  1. W6RZ

    W6RZ Premium Subscriber QRZ Page

    The SpaceX Starlink LEO satellites will be using frequencies as high as 30 GHz initially and up to 50 GHz eventually. I'd say the Doppler problem is solvable.
  2. K6CLS

    K6CLS Ham Member QRZ Page

    Seems to be a lot of that going around...
  3. KE2D

    KE2D Premium Subscriber QRZ Page

    Thank you. I stand corrected. Your number is correct. I had used an online calculator and left a default value set as one of the parameters which I should have checked and I misread the result.
    I redid the calculation with the original calculator and another one and I now concur that the number is about 2 MHz.

    This makes the Doppler shift problem far more manageable. Since the net Doppler shift is now only 4 MHz (+/- 2 MHz), none of the approach I spoke of above with a VCO in the LNB would be necessary.
    You could simply use an LNB with an LO of 75.53 GHz and it would produce an L band output in the middle of the 23 cm band (1270 MHz). This could be easily tracked by tuning the VFO of a conventional amateur radio such as the Kenwood TS-2000X. Alternatively, you could use an LO of 76.365 GHz and get an output at 435 MHz in the middle of the 70 cm band and there are many radios which could tune this range easily and cover the whole Doppler shift. Using 435 MHz as the IF may be simpler since the signal will survive better over coax. Of course you could also calculate other LO frequencies which would produce IF frequencies in the 2m and 6m bands if you preferred to use those (76.654 and 76.747 GHz). Each of those bands has 4 MHz of bandwidth and the majority of HF rigs today also cover 6m. I imagine LO stability will be challenging at that frequency.

    Now we just need someone to make us 0.2m dishes with tiny little LNBs at 76.747 GHz and a precise motorized tracking system. Calibrating the tracking system could be a challenge also I imagine. I wonder if the sun puts out anything in this range? It is only about 1/2 a degree in angular diameter and it's position is well known.

    If anyone was following the news about the SpaceX Starlink launch the other day (24 May) and your read the Wikipedia article about Starlink, you'll see that they plan to use the V band (75 GHz) in the future with initial operation on Ku and Ka.

    This would explain why Australian companies and government agencies are interested in experimenting with satellites operating in this frequency range. I suspect there is probably a lot of commercial and other interests which would like to gain some quick knowledge in this area. I don't think it's a coincidence that Starlink plans to use V band and that this satellite will be experimenting with it also.

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