Posts by OE3GBB

    Thanks to all for the responses. We are in an early stage of the project and your part is only to set up the antenna and RX/TX system. The communication part is done by someone else and we just know that part of it will be a high speed downlink on 13cm. To our calculations we are on the limit with a 2 m dish. So at the moment we are investigating the optimum for this setup regarding dish-size / rotator accuracy and speed / system costs. We also have to account for future developments as this institut will not be able to make a similar investment within the next 10 years.
    Anyway, further informations and reports are welcome.

    Our Amateur Radio Club OE3XNK has been asked by a local Fachhochschule to help setting up their satellite station. It is planned to install a 4 m dish for LEO cube satellites from 2m - 13cm. Prosistel is advertizing the PST71D-PRO + PST71E COMBO for this size of antenna. Is there any experience with this setup? What kind of dish will be appropriate, segments or one piece?
    73's Gerhard OE3GBB

    Hello dg0opk,

    TNX, but I did read this before. M0VKK did use the pallet with the smaller transistors 2x MRF7S21110HS, or? I am having the bigger transistors MRF7S21170HS on my pallets. I think the behaviour will be similar, but would like any comment before I start the assembly.

    73's Gerhard OE3GBB

    Hello All,

    I have two of these Andrew pallets, which I want to use in push-pull with 90° phasing. These amplifiers are each with two MRF7S21170HS transistors and Xinger XC2110E-03S. I have found some reports from Andrew pallets with other transistors, but not with these ones. From the Xinger parts data sheet I would assume, that each pallet could deliver 100W DATV on 2,3 GHz, from the transistors I would think of 2x170W-6 dB or about 75W in DATV.
    Has anyone used this pallet for DATV on QO-100 yet? I would need some experience reports and results in DATV, and also modifications, if necessary.
    Thanks in advance.

    Gerhard OE3GBB

    Hi George,

    Sorry, but I am not the right person to discuss that topic, I am just a tester.
    As far I have understood, the sampling of the voice in codec2 is 20ms and 40ms for lower bitrate modes. So 50 Baud is a pretty good match for any type of modem. To get the whole coded data over the channel, David has used several carrieres in parallel and used OFDM to get them as close as possible. Any other modems would be maybe possible and there might be some information about the theory on freedv.org or http://www.rowetel.com.
    In my view the easiest approach to get a best result regarding audio quality without neural network is to fill the 2700 kHz bandwith with as many carriers of 50 Baud. Using differential coding helps to reduce the BER.

    73's

    Gerhard

    Hi George,

    very interesting and good work!

    From the experiments with the original FreeDV mode2020 we know that OFDM and QPSK is not working over the satellite. The reason probably are the frequency / phase changes by LOs and doppler. So the quick work around by David Rowe was to change QPSK into DQPSK. With stable LOs on TX and RX this is now working without problems over QO-100. Maybe you also want to try differential QPSK?

    73's de Gerhard

    Today I have successfully modified the Opticum Twin LNB LTP-04H with S/N19-01-0xxxx.

    I left the crystal on the backside. I have cut the trace beween "2" and RDA3567. I have cut the meander trace "3" and soldered 470 nH in between. At "4" I soldered 100nF to cut the DC path to the PLL. The reason is that I am using a L-C-L LPF consisting of 2x 220nH and 100pF instead of the usual series resonance filter.

    At "1" I soldered 220nH. From the other side of this inductance I soldered 100pF to ground "5" and another 220 nH, building a LPF. The LPF was connected by a thin wire to the 100nF capacitor at "4".

    The right F-Connector was used as WB connection of the AMSAT-DL converter with LO 24 MHz. Using just 1 meter of coax, the signal level on 24 MHz was sufficient to lock the PLL. Did no further level tests for the LO at the moment.

    The cover has to be grinded between "1" and "5" not to have a short circuit.

    Test with a little 10.5 GHz radar source was successful.
    Tomorrow I will hook the LNB to my POTY and I hope I can report sufficient sensitivity and LO stability afterwards.

    73's Gerhard

    No, it is all different supplies. I was thinking therefore it could be a ground loop. Will try to feed the Plutos with HF-transformers next and avoid a DC-connection.

    I have found a solution. It was quite a simple error of my setup. I did have both Plutos at the same IP adress! Grrrrrr!!!

    Tnx, so the two vias are the connection to the crystal and the two "pads" are the capacitors. I think is should be possible to leave the crystal, cut one trace and use the other "pad" = capacitor as part of a voltage divider / LPF. I did not find a data sheet of the chip, so I don't know which side is the output of the oscillator.

    Opticum Twin LNB LTP-04H and S/N19-01-0xxxx is using RDA3567 and the crystal is on the backside. I think it is possible to cut one of the traces to the crystal right behind the Chip and before the via. LO input should be on the other trace, having a pad for soldering. Will try to modify and test.

    No, it is all different supplies. I was thinking therefore it could be a ground loop. Will try to feed the Plutos with HF-transformers next and avoid a DC-connection.