Posts by G0MJW

  • Hardware Needed for TX

    It is more sensitive than expected. You can just about do 2Ms with 25W QPSK 1/2 rate FEC with a 2.4m dish. Lower rates 125ks QPSK 2/3 FEC and 66ks 8PSK 5/6 FEC require under 5W and 33ks 8PSK 5/6 FEC even less.


    Multiply these powers by 4 for a 1.2m dish. So 2MS 100W but 66K only 20W.


    Thus 333ks and 500ks are achievable with a Spectrian or similar PA and a 1.2m dish. Many are using 50W PAs and achieving good results with 333/500ks QPSK 2/3 FEC.


    Make sure your feed is true RHCP or you throw away 3 dB. That's like cutting the dish in half.


    Mike

  • LNB-Kippwinkel (Skew)

    History.


    Broadcast TV was circular using the 12 GHz DBS band. There were plans for slots and beams for small and medium-sized vessels like the BSB Squarial. Launching a DBS TV satellite service takes time and too much time spent deciding on just what to do. Some of the fixed-rate satellite service operators were able to provide the extension of the existing 11Ghz Ku band services they were providing to cable heads etc. It would need a 60cm dish and one of the new low noise front end HEMTs but DTH TV in the Fixed Satellite Service D-MAC even, but far too late to market and in the UK at least failed as a result. The fixed satellite systems had used linear polarization so that's what stuck. The operators extended into the broadcasting bands and the satellites together with digitally allowed the small dishes we have now.


    The lesson, be first to market, do not dither about trying to get everything optimal and get global agreement on standards.


    Mike


    PS - S-band and then C-band used circular because of the faraday rotation. Not needed at Ku-band.

  • QSL & QRG???

    What universally matters is the frequency of the emissions, so I would log that. Amateurs should not cause interference and logging from the official view is mainly to aid investigating interference. Receivers do not interfere with anyone, unless they have spurious emissions. The transmitter that is being received have a license, with requirements for logging or not depending on how it is regulated. From the amateur perspective, logging the receive frequency is useful for cases of interference, or awards. Hopefully, the authorities will not be require a record of what amateurs are listening to.


    Mike

  • IP over DVB-S2

    Really? That's unusual I think. You Germans are lucky. Anyway, we are not really broadcasters in the usual sense of Sky, RTL, etc.


    Back to the point, I would be interested to try Satellite IP if we have a standard.


    Mike

  • DATV Beacon A71A C/N and signal strength decreased?

    You can be happy yes. I get at best 10.6 dB. This morning, with heavy cloud and no other users, it had dropped to 10.2 dB.


    When developing I noted that the phase noise is really important. For example, on the BBC transponder on BADR with an unmodified LNB I got an MER of 13 dB with a 1.2m dish. With a GPS locked LNB it was very much worse. This is a much wider bandwidth. It depends on each LNB and the phase noise of your reference. With that MER, I think you are OK.


    Mike

  • Converter 739 to 144 MHz oldschool style

    Most diode mixers are switches, on or off. Driving them with a square wave is exactly what they need. If you want to be really cheap and get from 739MHz to 2m all you need is a mixer, an LO source and an attenuator on the output. Performance will be .... well, it would be better with a filter or two.


    The LO source could be a cheap packaged unit, a packaged 600MHz oscillator costs €5. If you insist on 145MHz then pay big money for an si560 or similar and control it with the BATC board.


    DVB Tuners and lower IFs. Yes, or course, if you get the right one. This is what the Minitiouner does, IF from 144MHz to 2.7 GHz.


    Mike

  • IP over DVB-S2

    If you are going to be pedantic like this with respect to if it's called TV or not, I would point out amateurs are not permitted to broadcast so using DVB as a term is unwise. DATV-S2 perhaps or DA-S2?

  • Rücksprechkanal für QO-100 ATV

    Hi,


    I know this thread is in German, I use Google translate. I could use this to write but who knows what will emerge. I do DATV and happy to have an FM talkback, it would not be hard to implement. However, we are having some success with low symbol rate DATV that fits into 50kHz. Do not automatically assume that a low power portable system can not uplink TV.


    Mike

  • 2.4 GHz PA from Bisonelectronics

    Mine arrived yesterday too. There are actually two PAs and the cover looks easy to bisect. I will find a copper heat spreader, or ask for one to be made. Are there any existing suppliers out there ? Here is a scan of what we are talking about.

  • DATV Beacon A71A C/N and signal strength decreased?

    I think his settings will be optimum, my LNB required 25 MHz but I am not running less to have an LO of 9.5 GHz when puts all signals 250MHz higher and DATV signals into the range the Octagon SF8008 can receive them.


    I think the maximum was 11.7 dB with the 30m dish at Goonhilly.


    Mike

  • How to adjust best signal for the WB beacon on your dish

    This is not the best way to align a larger dish. The MER is a combination of uplink and downlink SNRs and also the transponder occupancy.


    It is better to look at the level of the PSK beacon (level, not SNR! ) with your favourite SDR application. You can use teamviewer, you can use an SDR by the dish or an SDR and a server via WiFi. For example if you had an SDR Server running on your PC you can look at the signal with your phone by the dish without all the baggage of teamviewer.


    This method allows very fine and repeatable detection of the signal levels. It also allows you to correctly set the polarisation by looking for the null on the opposite polarisation.


    Mike