Full- Duplex operation on the NB a cool and modern new way to go?

  • Yesterday I was observing a signal sounding a type of digital mode with approximately 3.5KHz wide staying there for hours, I made a record and posted in a QO-100 Facebook group asking what it should be? The answer: these were two Free DV signals next to each other and the OMs were testing full-duplex mode using FreeDV.

    I just put an advice that the NB tp should not be used for Full Duplex comms (IMHO) for both analog or digital modes, then few people seems to get really annoyed with that advice and most of them declaring their support to type of full-duplex operations, and this is great mode and the future of ham radio etc. So I may be really outdated here but I though that ham radio SAT operations by nature is full-duplex, where you tx in one freq and rx in another, but using just one freq, now it seems the new and modern way to go is to utilize several frequencies at same time for the same QSO, if this is the case please let me know the procedure, like what would be the off-set from one signal to the other, etc. May be the band plan allocation for the NB should be redesigned?


    Ed - PY2RN

  • Hi Ed, It is exciting to see that folks are trying to use different ways and tools to communicate on the satellite. If I am not mistaken, the current guidelines propose the use of non-FM signals with a bandwidth not exceeding 2700Hz. While you might have observed a 3.5Khz signal it was actually two signals close together. So, using FreeDV could be an option and for example D-Star is not. It is good to have a continuous open conversation within the AMSAT community and specifically AMSAT-DL on the opportunities and challenges of different modes, bandwidths etc., knowing that already a good amount of thought and discussion has gone into the current guidelines. At the end, amateur radio is and continues to be an experimental service guided by common principles. The current P4-A Transponder Bandplan and Guidelines "....might be updated regularly to take into account the operational experience." This is positive and applauded and shows that the guidelines are a living document.

    Hope this helps,

    73 Stefan VE4SW

  • I don't see that there is any issue with operating full duplex in any mode that is allowed by the bandplan. I operated full duplex occasionally on SSB on AO-13 and AO-40. The only difference is that this is being done with FreeDV. I think QO-100 is a great way of advancing the hobby with experimentation and it should be encouraged.

    Jonathan Naylor

    Callsign: G4KLX

    Locator: IO90TT

    QTH: Worthing, UK

  • Hello everybody,

    I am one of the people who participated in the experiments. But it was not hours for me. I have the NB and WB transponder on the screen for most of the day. In the area for the digital mode I see a maximum of 2 - 3 signals over the day. So there is no need for space at the moment. For my colleagues and me it was interesting to test how close we can drive both signals and which modes are the best (intelligibility, fault tolerance).

    I can not really find anything wrong with it here if you do experiments on the satellite as long nobody else will be disturb.

    Efforts should focus more on finding and switching off such "stations" as VE5BB. Or the people who disrupt the digital experiments with brute power.

    Amateur radio is and should always be an experimental radio service. As Stefan said, the guidelines are a living document.

    73 es cu sn de Joerg, DJ4ZZ

  • DJ4ZZ some people seems to be confused regarding this experiment that took place last night, I just posted in Facebook a question and I do not know why one of the participants has posted another different thread few minutes after totally ignoring my question, not sure why, then when someone answered to my question I put my opinion there, then I started to receive lots of inquires why I was thinking that etc, but in the first moment I just asked what was that what seemed a wide digital signal, that's all, I do not judge here if this was valid o not valid experiment. So good to know that it is permitted full duplex operation using different frequencies in the QO-100 transponder.

    I still think it will be a little confusing for all the stations to find out who is speaking with whom because we may use any type of off-set I believe and don't need to be so close like you guys were yesterday so in my opinion this breaches a little the amateur radio ethics, but many disagree with this as well, but it is OK we do not need to agree in everything :)

  • @VE4SW Hi Stefan thanks for your inputs, actually FreeDV I always enjoined it testing and participating on HF/VHF etc but seems on QO-100 there are few stations already too advanced for us which are trying to learn something, so I will keep out of this mode, at least on QO-100 :) Regarding the Full Duplex operations using more than one frequency, OK it may be an advance to the hobby, but I confess i this is not a mode that raises any interest to me.

    73 de Ed PY2RN

  • Thanks for your explanation Jörg, which puts it into a different view point.

    As long as the Guidelines are respected in terms of bandwidth and power, everything should be fine and such experiments are welcome.

    Sometimes I wish in general that there would be more "respectful" operating practices recognizing that this is a satellite linear transponder with limited resources and not just another short wave band or terrestrial radio.

    By this I mean also more understanding and interrest in efficient modulation and coding techniques for satellite communication over a linear transponder.

    Yes, we have a lot of bandwith, but the RF power is shared with all users,

    Indeed there are a lot of new ham radio stations never heard or practizised amateur radio satellites before.. so more education will be required too.

    When I read Ed's comments I was first wondering what is the benefit of FreeDV when occupying double bandwith for a return channel which is idle while the other person is speaking? That is even more bandwidth than a standard SSB QSO.

    Anyhow, I think with your explanation this topic can be closed.

    With regards to the spanish Pirate, with a lot of "silent" support of the community the person has been 100% identified. He even has a Facebook account.. That's the same person illegaly transmiting SSTV on the millitary fleetsat satellites.

    Unfortunatly the authorities are a little bit slow, but we hope with help from URE and IARU the issue can be handled. We are currently also seeking advice from ITU.

    But still suprising me that we radio amateurs were able to track down the pirate, that other "organisations" have not been able to do all the years before...

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

  • Hi Peter,

    I am very pleased to hear that the pirate has been identified.

    Let me just say a little note about free DV:

    Of course, the use of two frequencies for a duplex connection is neither economical nor meaningful.

    Although free DV has been around for quite some time, you still have to "play" a lot with the settings to make it sound good acoustically.

    Even if it decodes at all, what bandwidth and power is needed, etc. were things we tried. The second QRG was used as a "return channel" to report the result of the different settings.

    In "normal" operation, free DV is of course used in simplex or half duplex mode.

    My suggestion would be in the future here in the forum to post if experiments are pending.

    With the large number of groups in different social networks, it is unfortunately not possible to inform everyone.

    As far as my colleagues and myself are concerned, we will do nothing that could jeopardize the survival of this great communication opportunity for us amateur radio operators.

    73 es cu sn de Joerg, DJ4ZZ