Posts by PA3GUO

    Hi Ed,


    Looking forward to make a DATV QSO with you, I am ready for that now.


    Long time ago you were one of the 1st stations I worked on the NB transponder, that was awesome, I am sure other will love to make a voice QSO with you as well.


    Henk

    DB8TF, I get about 70W out of the bison PA. I did the snowflaking, but not changed the bias currents, just provided 28V.


    Now 90 vs 70 isnt much but stil interesting to explore. When I increase input more no further increase in output.


    You bias mods may give that 20W extra.


    PA is very stable I need to say, and does not get hot.


    Henk

    Just for fun I connected my Minitiouner to the Portsdown USB, picked the first signal I saw on the WB monitor from BATC, and there it was: immediately a decode of the 333ks signal of F5UII !


    Amazing !

    Henk

    PA3GUO

    Looks very good. :)

    By the way, the directional coupler at the output can be omitted and thus may bring a few tenths of dB more output power to the antenna. The amplifier already has a coupler built in and you can simply connect the power meter to the second MMBX socket. The corresponding calibration value has to be determined of course, but this would be necessary for the external coupler as well.

    But one could also realize a deluxe version and use the external coupler to measure additionally the reflected power.


    With the 25 euro power meter via Ali connected to the directional coupler.

    very nice!

    I do not have a spectrum analyzer, but a quick and dirty set up this afternoon using a pluto SDR looked quite OK. My portsdown (plus small LNA) connected to the input gave 44dbm on the output for a 125ks stream. Power supplied 27,5v and 5A.

    Need to do some proper measurements tomorrow.

    Henk

    We need to be careful, for DATV we need to be within the -1dB compression point/range.

    Seems to be at 6dbm input, but of course, all this is my initial result.


    Also, check using an SDR, eg an Airspy, the spectrum of the portsdown output, the shape should not be distorded, the socalled shoulder for example.

    DF2HF,

    I did not modify mine yet.

    I started at 16v, moved to 24v, and did some more tests at 28v.

    Clear that performance/gain at 2250 MHz is 10dB better than 2400MHz.

    Input was an RS signal generator.

    So I will next snowflake the PA to get the higher gain also at 2400MHz.

    The tables give the initial results.

    My goal is DATV, intended use is to connect it to a Portsdown TX.

    What is your goal, WB or NB usage?


    Henk

    G0MJW yes, all 4 LNBs are unmodified. I started with 2 identical ones, and later added 2 others from a different brand/design, as I wanted to make sure it wasnt a difference in design. The 2 new ones performed identically, and both also when mounted in the dish 3db better as the previous ones mounted in the POTY. Then I removed from one the horn antenna and placed that in the centerpoint of the dish, with a POTY lens, both via a copper wave guide (from the POTY kit) and directly: 3db lost.


    All using same receiver and cables&connector only swapping LNBs.


    Dish 1 Triax 90cm offset

    Dish 2 120cm offset

    For the NB transponder I use a POTY, a very practical single dish solution.


    For the WB transponder I noticed that a bare LNB in the focal point (not via the waveguide/pipe of the POTY) gives me 3db extra SNR (MER of the beacon goes from 3 to 6db on a 90cm dish).


    Also on the NB I receive 3db more signal on an unmodified LNB.


    I also tried with only the waveguide (copper pipe) (without the POTY) on an LNB with the horn cut off: also 3 db less. With or with out lenses, with multiple LNBs, with varying position within the focal point, on a 90 and a 120cm dish.... a bare LNB seems always 3db better.


    Also I see that quite a lot DATV WB stations use 2 dishes...is this the reason?


    I can imagine the horn antenne that is cutt off results in a loss, but isnt a lense to resolve that, or only partially?


    PS I need those 3 db extra for DATV reception, without I only decode the beacon at max 3db


    Thanks

    Henk, PA3GUO