DATV Talk-Back Channel (Narrow 12,5 kHz FM) in WB-Transponder ?

  • Receive my first DATV- Picture (on4bhm) from WB-Transponder today. Thanks to the Quatar/AmsatDL -Team

    Easier Experementing if can Talk-Back. What do you think abaut a Narrow FM-Talkback-Channel lower/upper the Beacon ?

  • Personally (which is just an opinion) I don't think it's a good idea to produce FM on the NB linear transponder. If people want to talk back use the WB transponder, or better... two persons uplink .. and they can see AND hear each other or .. leave your picture black (or whatever produces the least band width) and uplink (digital) audio ?

  • Thank you for reply, Remco. I mean only the WB-Transponder for a narrow Talk-Back-Chanel, never using the NB-Transponder for FM.

    Follow Situation: One Station transmit DATV and 10 are only looking (Not all have the Power for a DATV-Signal). They have no easy way to communicate with the transmit Station. In Germany we have Talk-Back-Voice-Receiver in every ATV-Repeater, nice Contacts for Non-ATV-Transmitting-Stations, making Tests and Comunicating very easy. If you see the Spectrum you have no Idea abt Parameters, you call on a fix Frequency and hear what going on.

  • DL4SAC I know the talkback for ATV (here on 144.750) ... but ... 'not all have the power for DATV-signal' <-- bad luck !!

    So, it's simple (in my opinion... which is just an opinion ...) when you don't have the power ... don't (want to) talk back (!)

  • Thank you for reply, Remco. I mean only the WB-Transponder for a narrow Talk-Back-Chanel, never using the NB-Transponder for FM.

    Follow Situation: One Station transmit DATV and 10 are only looking (Not all have the Power for a DATV-Signal). They have no easy way to communicate with the transmit Station. In Germany we have Talk-Back-Voice-Receiver in every ATV-Repeater, nice Contacts for Non-ATV-Transmitting-Stations, making Tests and Comunicating very easy. If you see the Spectrum you have no Idea abt Parameters, you call on a fix Frequency and hear what going on.

    I totally agree with you.

    I have been working on ATV for 20 years now. Without talk back channel sometimes is almost impossible to work ATV, DATV even more. For example on our local ATV repeater we have option to mix audio from 144,750 to main sound carrier. Chat window alongside WB monitor SDR is ok, but is already overwhelmed with messages.

    Without talk back channel only big stations can take part on ATV, and receive-only stations can not contribute in the ham way.

  • SSB on NB transpoder is ok solution, but it has some drawbacks.

    Not all stations can achieve prefect frequency alignment, so it might be hard to operate DATV and adjust talk back frequency. Ad to this multiple operators on same frequency with short conversations. It is not going to work.

    Also NB transoponder uses vertical polarisation and WB horizontal.

    Another thing is simplicity. For example I put my HT near cable from LNB and can hear beacon and all SSB stations. If they were on FM it would be perfectly receivable. Also it is much more easy to transmit in FM than in SSB. Maybe some hams are not interested in SSB work.

    There are more reasons...

    Talk back is add-on to DATV and should make QSO easier, not make challenge itself. Grab a HT instead of telephone talk.

    That's my personal view of talk back channel.

    Could weak NBFM channel cause some disturbance to DVB carriers?

  • Did some testing on both ideas...

    Recently i am able to be QRV on NB and WB in same disc and amplifier..


    Doing NB USB is a good option but indeed far from perfect. zerobeat signals and squelch problems makes it less preferable for the DATV station.

    NFM or even WFM will fit easy between WB channels and is better in respect of quality and easy to use.. You can better work with squelch options and even CTCSS.. Downside, youll need over 10Watt FM to get a desent S9 R5 signal...

    In stead of the 4 watt needed for a similar USB signal...


    You can even put the NFM channel inside the DATV signal but youll get lots of white noise in the reception and the D quality of the DATV signal goes down rapidly...

    So that not wat one should want...


    Normal 2 way QSO on DATV is still not so easy as there is a big delay in coding and decoding causing up to 15 sec waitings in microfoon hand overs....


    So what would be the reason not to use NFM in the WB section of this nice project other than it needs to be allowed??


    Benno...

  • Downside, youll need over 10Watt FM to get a desent S9 R5 signal...

    In stead of the 4 watt needed for a similar USB signal...

    Hi Benno,


    This is already the reason.. FM is the most ineffective method on satellites and we just don't want to promote this among other technical reasons. We also have had abuse in the past using strong FM on both NB and WB.. There have been a period of experiments using FM as a back channel, but it was not feasible for the above reasons and that's why we banned FM in general on QO-100.


    73s Peter

  • You could always try to do talkback with DATV. Just set to send an audio stream only. This way you should be able to use 33ks without problems. This is really only practical when making your own transport stream. The Pluto could probably do this by itself if @Evariste was inspired to develop the option.


    Mike