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40cm dish

  • David IW5BNL
  • Sep 29th 2019
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  • David IW5BNL
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    • Sep 29th 2019
    • #1

    Hi


    I'm using 40cm ofset dish and octagon LNB.

    After pointing optimization I get that beacon level is 9Db over noise flow.

    Is it a realistic number with so small dish?


    Thank you


    David

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  • DK2ZF
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    • Sep 29th 2019
    • #2

    YES, it is

    DK2ZF JO43VH


    using 60cm portable or 1.40cm from home

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  • David IW5BNL
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    • Sep 29th 2019
    • #3

    Thank you.


    David

    IW5BNL

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  • DL9SEC
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    • Sep 29th 2019
    • #4

    @IW5BNL

    Hi David,


    Quote from David IW5BNL

    Is it a realistic number with so small dish?

    For my reception experiments I use a 35cm camping dish on a tripod on the ground, a TCXO modified OPTICUM LSP-02G and a NOOELEC RTL-SDR with a 10dB attenuator at the input.

    I have the beacon peak at about 25dB over noise floor (see attachment).


    73, Thorsten

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  • ON7CL
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    • Sep 29th 2019
    • #5

    What is the type of the camping dish ?


    Tnx, Rudi - ON7CL

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  • oh2aue
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    oh2aue
    • Sep 29th 2019
    • #6

    S/N ratio is, especially for CW, a function of detection bandwidth, or in the case of an SDR, a function of sampling rate and fft size. For a regular analogue radio with real HW filters, the CW power is (hopefully!) considerably more than the noise, so the (peak) power measurement will fairly accurately depict the carrier energy level with even quite wide detection bandwidth. For noise however, we need to consider the noise bandwidth. The broadband, filter passband-filling noise power (which should be detected in RMS by the way) will be highly dependent on the bandwidth of it, i.e. how much noise energy is being integrated into a number. Increasing the detection bandwidth from e.g. a ~300Hz CW filter to a ~3kHz SSB filter will result in 10dB more (noise) power. In other words the CW carrier S/N ratio will appear 10dB worse with a 3kHz filter than a 300Hz filter


    The point is, to make any kind of S/N ratio comparison, we need to know the modulation (CW is very different from 400BPS PSK) and we need to know the detection bandwidth. And in the case of SDR it is important to know the sample rate and FFT size (bin count). Only in this way can we compare apples with apples or make orange/apple conversion calculations to make comparison possible.


    And for really meaningful S/N measurements, peak detection should be used for the (CW) carrier (S) and RMS detection for the noise (N).


    It does not hurt to realize that the noise factor (N) is often noise + interference (I) and that a more accurate measurement would be S/(N+I), but fortunately for us, due to it's very high linearity, the QO-100 transponder noise floor has been and is pretty much random noise. In AO-7, AO-40 and the like, this was not so simple as HELAPS and other high efficiency RF amplification and other linearization and non-linearity processes resulted in noise-sounding (N+I.)


    The result of all this is that 9dB SNR can easily be the same this as a 25 dB SNR. Only the measurement conditions are different.


    73 - Michael, oh2aue

    ---

    "If you have data, you have something, if you do not, you have nothing." (Bengt Hultqvist, SK 24.02.2019)

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  • David IW5BNL
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    • Sep 29th 2019
    • #7

    Hi Thank you for answer.the

    I'm using following method for measuring S/N ratio :



    1) I made I^2+Q^2 average it over 1Sec. I and Q samples are collected at 16K sample rate. and after 2.7KHz ssb

    2) I made ratio between reading when I tune the beacon and when I tune just the noise.



    I fully agree with Michael that depend on modulation. Using FFT (That show the peak) I get about 10 db higher.



    Do you know if exist a standard?.



    I also have some tree in front of the dish but the blockage should be vey small.



    Ciao




    73,David

    IW5BNL

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  • BG0AUB
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    • Sep 29th 2019
    • #8

    iw5bny What is the elevation Angle of your QTH antenna?

    BG0AUB-Urumqi, xinjiang, China - NN33SV

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  • David IW5BNL
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    • Sep 29th 2019
    • #9

    BG0AUB : it's about 38°

    The dish is a offset for camping


    David

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  • DL9SEC
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    • Sep 29th 2019
    • #10
    Quote from ON7CL

    What is the type of the camping dish ?


    Tnx, Rudi - ON7CL

    Question addressed to me?


    A Megasat offset camping dish (35/40cm)...

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  • ON7CL
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    • Sep 29th 2019
    • #11

    I will use one for my portable operation with helix feed 5 turns :)

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  • David IW5BNL
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    • Oct 5th 2019
    • #12

    Hi


    After better point of Antenna and lnb position I get becacon (pk with FFT) 21-22Db. That is ok for 40cm dish.

    It's the time to think to the TX.

    I'm thinking to use Pluto..Anyone had experience with with it on NB transponder?.

    Some picture on my GNU radio RX locked on upper beacond and antenna.


    David

    IW5BNL

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  • ON7CL
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    • Oct 13th 2019
    • #13

    Hi, 40cm camping dish will be here this week :)

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  • DF5SF
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    • Oct 13th 2019
    • #14

    Hi,


    whats the gain of a 40cm dish at 2.4 GHz and how many power do you need for upload with a good signal ?


    Thanks

    Uli DF5SF

    73

    Uli

    DF5SF

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  • ON7CL
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    • Oct 19th 2019
    • #15

    Yesterday we tested the portable uplink for the Es'hail / QO100 Satellite, with the 40cm dish, the Helix with 5 turns, 5 watts was enough to reach the Satellite 😀😀

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  • David IW5BNL
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    • Oct 19th 2019
    • #16

    hi


    Very good!

    Do you use a helix for uplink?

    I'm progressing on transmitter.


    David

    IW5BNL

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  • ON7CL
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    • Oct 19th 2019
    • #17

    Ciao David,


    Yes like you see it we used it :) with the helix.


    The radio is a Yaesu FT818 using 0.5w, into SGlabs transverter + amplifier. Output 5w :)


    73 - Rudi - ON7CL

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  • David IW5BNL
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    • Oct 19th 2019
    • #18

    Hi Rudi,


    good thank you.I will use more or less same power and Helix.See you soon on sat.


    David

    IW5BNL

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  • ON4BCB
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    • Mar 5th 2020
    • #19

    As the 40cm dish has a F/D of 0.5 a poty is performing better then a helix, and more compact


    15-20w is needed to be at the beacon level

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  • G0MJW
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    • Mar 6th 2020
    • #20

    A 40cm dish has 18 dB gain at 2.4 GHz. Another potential portable uplink antenna is a standard loop yagi which would need to be about 1m long. Potentially easier to fit in travel baggage if it splits into smaller lengths. For RX you still need the dish though so a dualband feed might be the best answer.

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