Posts by HB9SLV

    Hi,

    Has someone tried this amp?

    It is advertised as a 2-W amp. If this is true, it would be quite convenient to mount the device right at the focus of the dish, because it looks much smaller thant the usual wi-fi booster, and maybe more weather-resistant with its shhrinked-plastic cover.

    They claim 11dB Tx gain (and 10dB Rx gain) and require a 3.7-5.5V supply. Input power is +4 to +20dBm.

    I suspect they'll run quite warm but it doesn't look too hard to strip off the heatshrink cover and attach a heatsink.


    https://fr.aliexpress.com/item…de-452d-b12a-b7bc705c07af



    73s

    Then I assume that in the case of DATV, the noise floor of the transponder must not be as easy to see as it is on the NB transponder.

    Because if you can clearly see both the level of the beacon AND the level of noise on the screen of your receiver, using a small dish, then using a 30-meter one would have the same effect as running the received signal through a (linear) amplifier. The sihnal/noise ratio would not improve.


    This is the very point of this thread. Why should a larger dish improve the signal/noise ratio of a received signal from the Oscar 100 transponder? This signal is broadcasted by the sat with a given s/n ratio, which cannot be improved lest breaching some thermodynamics law:).

    Maybe the benefit of a better dish illumination was canceled by signal absorption within the lens.

    I was planning to carve a lens to be fitted in front of my LNB, to improve efficiency. The material I was planning to use is wax. Candle wax. Wax being a good dielectric, losses should be low, I hoped.


    So I melted a few candles into a cylinder slab 2 cm thick. The first thing I measured was the attenuation brought by 2 cm of wax in front of the LNB. I measured 4 dB with SDR console. This is about what I was expecting to gain with a better dish illumination.

    Needless to say, I shelved the project.


    A better way ( no absorption losses) should be a secondary reflector. There was such a project in a recent DUBUS issue.

    @HB9LSV, the signal to noise ratio at the transponder output depends on your uplink power.

    Hello Andreas and thanks for your answer.

    You are right, of course. What I should have asked is : " what is the signal to noise ratio of the high frequency beacon?"

    Because if it is 20 dB at the satellite, as I see it here with my system, there is no hope I can make it better with a larger dish.


    But if a station sends a weak signal to the satellite, let's say 100 mW and a 60 cm dish.

    The transponder will output it with a small signal/noire ratio. Let's say 5 dB,

    Will I be able to decode this better with a larger dish?


    /3s

    HB9SLV Try if you can distinguish the tpx noisefloor and your system noise floor with a wider span (2 MHz or so).


    If you can distinguish, how much is it?

    Here is what SDR console says about the Noise floor:

    On 10.495 GHz: -94 to -97 dBm

    On 10.489 GHz: -94 to -96 dBm

    On 10.483 GHz: -95 to -97 dBm


    The high frequency beacon : -73 to -78 dBm.


    I think I got the point. The noise floor I am seeing is the same within or outside of the tpx band. This means that this noise floor that I am seeing is produced by my LNB.

    With a larger dish, the noise floor will remain at the same value but the beacon will be stronger.


    Does someone know what the s/n ratio is at the output of the transponder? I started thinking about this when I read on this forum that a few months ago, it was decided to lower the noise floor at the output of the transponder to save energy on the sat.

    Hi all,

    I am currently using a TV sat 80 cm dish, an unmodified LNB and an RTL SDR.

    When monitoring the NB transponder in SSB, SDR Console shows a noise floor at about - 90 dBm and the upper beacon some 30 dB above the noise floor.

    Is there any point in using a larger dish?

    Signals will certainly be stronger, but so will the noise floor too, with the s/n ratio still at 30 dB..


    What do you think?


    73s