RX antenna gain on the QO-100 / pathloss

  • I am trying to calculate the pathloss and sensitivity of QO-100 transponder. Calculation:


    Au = 20 x ( - 4.622 - log f - log L)


    Au - pathloss in dB

    f - frequency in GHz

    L - distance in km


    My calclation shows that the pathloss is around -192 dB.


    My own carrier with 33dBm (2W) with 24dBi antenna is 20 dB over my noise floor. I am receiving with 80cm, LNB and SDR dongle. But I know that there are stations with better receiving conditions.


    My receiving floor:

    -192 dB + 33dBm + 24dBi + 20dB = -115dBm (0,4uV/50 ohm)


    But I don't know what's the gain of receiving antenna of QO-100. Did anybody knows that? And are my calculations right?


    What's Yours receiving floor?

  • You can calculate/estimate the 'receiving gain' of the QO-100 antenna assuming that the satellite is on 38500 km above the Earth and needs to illuminate the whole Earth with minimal 'spill over'. Assume (I don't know exactly) that you've -3 dB points at the edges of the Earth, then you can calculate the (-3 dB) opening angle and from that you can calculate the 'gain'.

    But there is a calculation concerning the uplink budget in the formal/original Es'hailSat presentation for the ITU (some years ago).

  • we would need some "reference".

    We can measure the dBm value at the LNB's output, but what is the conversion gain of the LNB ?

    It will be different for various brands ?

    Has somebody already measured this conversion gain ?

  • om0aao you are in the right ballpark and you can use the cited document as further guideline. There is only so much we can say due to NDA's but not only do you need the satellite RX antenna gain but also its noise temperature. That is why G/T is quoted in the above table.

    And then of course are there some more confidential numbers for the downlink part..

  • How I read that sheet: these are worst case numbers (second bullit).


    In the sheet the word 'Europe' is not mentioned, at least I do not see it.

    'Coverage peak' <-- say cantral part of the footprint
    'EOC' <-- end of coverage (say 5 - 10 degrees elevation)
    'Elsewhere' <-- well ... elsewhere ; -)

  • How I read that sheet: these are worst case numbers (second bullit).


    In the sheet the word 'Europe' is not mentioned, at least I do not see it.

    'Coverage peak' <-- say cantral part of the footprint
    'EOC' <-- end of coverage (say 5 - 10 degrees elevation)
    'Elsewhere' <-- well ... elsewhere ; -)

    OK, 'Coverage peak'. We are in Europe also in the Coverage peak. Thats I meant. You say these are "worst case numbers". How many dB or Watt would you add ?

  • One thing not to forget: Plenty of WX conditions can effect your overall loss. For example, in the early morning if the sun is on my dish, I can see the noise floor higher than at late at night.


    Then we have cloud cover. At both 'ends' of the "QSO" (or Beacon Uplink site, or GHY Downlink). Let alone rain drops on the dish, at either ends! Here in the UK they are threatening hail today, so that might well be an interesting effect!



    Which brings up something else I've been thinking about over the last few weeks...Would weather reports from key sites (Bochum, QARS, Es'hail Satellite Control Centre, GHY etc) on the Upper Beacon be useful ?


    I know there's times I've gone "Where did 6dB go ?! I had 14dB SNR last night, what's changed in 7 hours!", so gone fiddling with the feed position to no avail, and *then* find out its windy and raining in Bochum, or looked up at the sky here! Ditto with Goonhilly.


    (If you are comparing your system to the Beacons, and/or GHY's SDR, then you need to make sure you are aware of local conditions at each site)


    If there's interest in discussing WX and other environmental effects, we can start a new thread (I really just wanted to point out that the WX can effect these measurements on this thread, having been caught out myself)



    73s


    Iain


    (and as if by magic, 5 minutes after I post this, the great attenuator from the sky comes down in liquid form...British Weather, have to love it!)

  • I have no insight information, so the following is an (educated?) guess: Looking e.g. at BADR4's Ku-band footprint (which is not a global beam!) you see that in the centre it's 50 - 51 dBw and at the edges 6 dB (or more) less, which translates to dish sizes in order to receive the TV programs.


    The transmit Esh2 Ku EC-horn has 17 dBi (see specifications), so this translates to a certain -x dB (x being the design specifications) beam width from which the relative loss / output power can be derived. Because the beam is global I think around 6 dB may be added .. which translates to half dish size.

    Cf the sheet: 89cm dish at EOC vs 50 cm dish in Coverage peak = 'around' 6 dB (5 dB to be precise).

    Of course the values in the sheet are the design goals, so I am not aware which values are realised ... I did not sign any NDA concerning Es'hail-2 ; -)

  • OK, 'Coverage peak'. We are in Europe also in the Coverage peak. Thats I meant. You say these are "worst case numbers". How many dB or Watt would you add ?

    Europe is not in the coverage peak. The coverage peak is at the nadir direction of the spacecraft, which is actually in the Democratic Republic of the Congo (90 deg elevation). With elevation of 33 deg for central Europe we are closer to the EOC (edge of coverage), hence the "75cm elsewhere" recommendation.

  • Thanks to everybody for a lot informations!


    I agree with g7iii that the WX can ruined signals. Both on downlink and uplink.


    Found that most stations use power 1 to 4 watts (30 to 36 dBm) and similar antennas but... the signals on the downlink varies more than 6 dB. That means some stations loose decibels somewhere.


    My question is if my station is working properly (NOT) and how weak signals I can receive.


    Now I can receive 1dB over the noise floor station with 24dB antenna and 25mW or 10dB antenna and 0,63W. As said G7iii - in ideal conditions.


    I will make more tests and try to make a small research... TNX!

  • Rain attenuation in dB/km can be seen below. From the graph it is clear that 2.4 GHz is not much affected by rain. (except when water gets into the feed itself and ruins the matching).


    For 10 GHz it can be a problem, but then it has to pour down. There are lot of information on Sat-TV and rain attenuation on the internet. One report stating that: "For Western Europe rain attenuation only excees a couple of dB in 0.1% of time".


    73 Ole


  • Europe is not in the coverage peak. The coverage peak is at the nadir direction of the spacecraft, which is actually in the Democratic Republic of the Congo (90 deg elevation). With elevation of 33 deg for central Europe we are closer to the EOC (edge of coverage), hence the "75cm elsewhere" recommendation.

    Ah I see Achim, tnx 4 answer.


    73