Downlink with own antenna or web-SDR?

  • Hi,


    I am planning to install a downlink (mod LNB, GPSDO, dish with pole, SDR) for reception of QO-100. In future I will plan an uplink.


    Why is it actually worth to use an own downlink? There are many web SDR available to receive the satellite.

  • There is no chalenge to hear WebSDR, but its one to build its own "downlink". You are SWL - Why ? You could listen Web-Radio instead. WebSDR is good and OK to control its own transmitted signal.


    I wish you good luck by your setup and future HAM license.


    73

  • SWL-Max I have been using both of your methods. Given a reliable internet connection for the web SDR and a decent dish size for the local LNB + RTL-SDR, the results are not much different. Only a small additional signal delay of the internet connection is noticable. If you only want to listen and if you do not need the technical challenge, as mentioned by HB9SKA, then web SDR is fine for you.


    You did not mention a 3rd method which is worth to test in case you plan to transmit. A modified LNB with a normal receiver, no SDR. This reduces the signal delay significantly. If you do not like to hear your own echo with a long delay try it.

  • I would encourage you to make a simple RX , rather than rely on someone else's receiver :) It is really, really easy.

    I documented my "do it with as little effort as possible" approach on QRZ here - https://forums.qrz.com/index.p…00-and-a-plutosdr.660334/ - that is about getting both TX & RX working with a Pluto, but it talks about my original RX set up like this: :


    "I had already set up a super simple system for receiving the narrow band transponder for the geostationary satellite QO-100 (Es’hail-2). It consists of my 80cm offset (steerable) dish I use for TV, and an RTL-SDR connected to the “loop out” of my sat TV receiver. I just pointed the dish, set up a transponder in the TV box and the signals were there, around 739 Mhz (10.489675 Downlink freq − 9.75 LO frequency of the LNB = 0.739675 GHz = 739.675 MHz) . Then, using SDRConsole I was able to set a receiver offset and then “lock” the software to the beacon ( https://www.sdr-radio.com/Console/EsHail2 ) and there was a useable receiver system, with very little effort!"


    Give it a go! experimenting is what the hobby is all about ;)

    73 Neil

  • I think it could be interpreted that in the case of the U.K licence it requires that your “Radio Equipment” be capable of receiving on the frequency upon which transmission takes place. I’m not a lawyer but the language, to me, in conjunction with the rest of clause 7 of the licence conditions implies that it is the licensee’s equipment that should be receiving and not that of a third party.


    “7(6) In order to reduce the likelihood of causing Undue Interference, the Licensee shall ensure that the Radio Equipment is capable of receiving Messages on the same frequencies and with the same classes of emission in use for the transmission of Messages by the Radio Equipment.”


    Besides the above offline monitoring of the stations transmitter into a dummy load should go some way towards reducing the number of poor quality signals that have been appearing.


    Personally I would not consider transmitting without being able to hear my own signal locally. QO-100 is not a piece of test equipment and using it as such cannot do anything to enhance the reputation of the amateur radio community in the eyes of the satellites owners.


    Clive

  • Not trying to be awkward here, but how many actually have a receiver to monitor the transmit frequency on 2.4GHz and not what have been rebroadcast through the satellite. To me that is what 7(6) means. It is correct in that QO-100 is not test gear, but the assumption is that if sounds clear through the satellite then it is OK on transmit. Although down at 2.4GHz who knows what spurious side-bands or image frequencies are being transmitted, they are going upwards so will not effect anyone, will they?????


    There was an interesting read on QRZ at one time about a security camera effecting a 1.8GHz sat band,

    https://forums.qrz.com/index.p…nterference-issue.659731/

    and a pdf about the levels of interference

    https://www.itu.int/en/ITU-R/space/workshops/2017-Bariloche/Presentations/23- Elena Daganzo - ESA.pdf

    I wonder if we can do harm to systems on other satellites.


    Adrian

  • Well each to their own but I stand by my opinion. Some earlier words on the forum regarding 2.4GHz RX maybe of interest...


    2,4GHz transmission check


    Not to ignore the original topic completely... I would also encourage any one wishing to operate QO-100 to have their own 10GHz receive capability. It is not difficult to achieve especially now with the popular SDR console software from G4ELI carrying out frequency drift correction.


    Clive

  • G8UGD I have. I have two actually: a 2400 - 144 MHz AO-40 converter and a 13cm (2320 MHz) transverter where I mix the RX IF-signal down to 144 MHz with a 80 MHz 'crystal block' and a diode.

  • To the original poster, to me it is a good idea to have your own downlink as:-

    1) it's yours

    2) Should be less latency then Internet based

    3) May be fun to put together

    4) build it portable enough and you could use it anywhere.


    As to the point of monitoring ones own transmissions, it was good to notice that many have the gear to make the checks and where doing so before the satellite was live, I would surmise that many are old hands at satellite working. I was not, but thankfully had a Hackrf that works to 6GHz to hear my output directly.

    What I was trying to suggest was that a dish, 10GHz LNB and say a SDR with software does not necessarily provide compliance with licence conditions.

    But I thank you for the link to the 2.4GHz transmission test as I just decided to get two of the MMDS converters at £8.50 each that were mentioned by PA0P together with mod instructions.


    Adrian

  • There seems to be a lot of users with uplink only and completly depending on the WebSDR...


    Which brought me to the following idea:


    How about a "Virtual Transponder" in the cloud?


    Imagine a server creates a virtual passband and you can tune into it like with the existing WebSDR.

    Than imagine that you can transmit like with SDR-Console!

    Instead of actually radiating RF and receiving RF, everything is handled by Software on the Server and you are just streaming IQ data via internet in both ways.


    Does'nt this sound great? ;)

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • DB2OS That already exists. People making 'QSO's' via the internet (no, I am not talking about Echolink ; -) because they can't install an antenna or experience too much QRM.

    Not sure what you mean exactly... I know there is Brandmeister etc. on Internet and you can use it even without RF...


    I was talking about a virtual linear transponder with say 1 MHz bandwidth and "analog" tunig..

    enough room for SSB, FM, DSTAR, etc.. linear modes, digital modes..

    Even LEILA-3 with notch filter could work, or even better the STELLA with adaptive leveling of all signals ;-)


    So for what do we need QO-100 than?


    Gentlemen, I was joking !!! :D:D


    At least for me, our hobby still is about wireless radio..


    73s Peter

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • Great idea - lets call it Zello!