Posts by OE3GBB

  • Adalm Pluto & GPSDO

    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.

  • 2.4 GHz PA from Bisonelectronics

    Hi Thomas, I have the same problem. I do have a double unit and do want to combine them for double power. The right amplifier is doing well, but the left one is oszillating. Did you find a solution yet?

  • Adalm Pluto & GPSDO

    An interesting problem came up yesterday, when I was using two Plutos in parallel from the same LO. One pluto for NB and the other with Evaristes firmware for DATV. Both connected via LAN to PC and LO connected by -3dB splitter (in this case LO from the 40 MHz output of the AMSAT-DL-Converter V3). When I switch on the second Pluto the first one is stopping. It seems that the LO signal is dropping because the decoupling by my splitter is not sufficent. Any ideas? Will have to use a distribution amplifier for frequency standards?

  • OPTICUM LTP 04H Twin LNB

    Quote from DD5ER

    The Opticum Twin LNB LTP-04H up to the S/N: 18-08-0 xxxxx is in any case easy to modify.

    For the S/N with 18-12-0xxxxx and 19-01-0xxxxx we are currently investigating whether a modification is possible with reasonable effort.

    At the moment we still have a larger quantity of the LNB LTP-04H from the 18-08-0 series, which are now being modified. We ask for some patience here

    Hello, I have a model 19-01-0xx. Any news about modification?

    73's Gerhard

  • Nomographs for Parabolic Reflector Antennas

    Hi Rasto,

    many thanks. Now I am beginning to understand. Before knowing your paper I was thinking that it is sufficent to choose a feed where the -10dB angle of the feed equals the SA of the dish. But it is much more complicated :-). The approach to find a feed for a basic paraboloid and considering AET is clear now. But you also showed that without simulation there is no way to find the least 1/10 of dB Gain. It also shows that the whole setup offset-dish and Helix feed is quite forgiving.
    Thanks again.
    73's Gerhard

  • Nomographs for Parabolic Reflector Antennas

    Hi Rasto,

    thank you for all this very interesting informations. It made me get deeper interested in parabolic theory and made me read some technical literature about. So I now understand that for offset dishes the values for f/D and SA in the data sheets do not correlate. I allways thought that we should choose the feed to get -10 dB (or -12dB) for the actual SA. But according to your paper that is only true for H=0. Do you have an easy to understand explanation, why we have to first find the f/D for a virtual dish having same SA, and than the find the optimal gain for that new f/D? Why is it not sufficient just to design the feed for the SA of the dish?

    Thanks for your help!

  • MY QO100 SETUP

    Hi George,

    I checked your GNURadio graph. Congratulations! I just know a little about it. Tried it a few years ago, but no success. Maybe we could discuss a repeater setup on 70cm for FreeDV using Pluto?

    Regards

  • MY QO100 SETUP

    Hi George,

    that sounds great. Tonight it's too late as it is midnight soon, but I think tomorrow (sunday) evening will be fine. I will check 10489.646 at 16:00 UTC, or send me another time.

    73's Gerhard

  • Frequency Stability of the QO-100 NB Transponder

    Hi George,

    Thanks for the plots. What I am really interested in is the possible frequency change because of doppler within one symbol at 50 Baud, that is 20 Milliseconds.

    Background: I am very active in digital voice for years on HF and now also on QO-100. If you check http://www.freedv.org you will find different modes for DV, all optimized for small bandwith and noisy HF channels. David Rowe has done an outstandig work for the amateur radio community during the last decade.
    Mode1600 is using 14 carriers DQPSK each at 50 Baud over a FDM modem. This mode is very robust over the satellite with perfect synchronization and low bit error rate. See: http://www.rowetel.com/?page_id=2458

    Mode2020, a new mode using neural network technology for enhancing audio quality is using QPSK and OFDM modem. First tests over the satellite showed, that this setup is not working and a new modem should be developed. As a quick workaround David changed QPSK to DQPSK and now we can use mode2020 over the satellite. See: http://www.rowetel.com/?p=6920

    But with problems: A highly stable equipment on TX and RX using GPSDO is necessary. And there are sometimes problems with first synchronization and loss of synchronization during a transmission.
    I have made some single tone recodings over the satellite to find the problem.

    David Rowe analyzed the files an came to similar results regarding frequency change as you. See: http://www.rowetel.com/?p=6996

    At that time we did think the problem comes from a frequency change of the transponder or the earth stations LOs.

    My question to you mainly shall show the influence of doppler to that problem.

    I hope this discussion will also help you and others to enlight the problems with digital transmissions over the satellite.

    I think we still have to learn a lot.

    73's Gerhard

  • Nomographs for Parabolic Reflector Antennas

    Hi, the phase center is the virtual point where the beam of the electromagnetic field is emerging. This point is depending from the taper of the helix and the form and size of the reflector.
    See: Helical Feed Antennas Paul Wade W1GHZ ©2002
    The phase center should be adjusted into the focal point of the antenna. Therefore a mechanical means for adjusting a helix in 3 dimensions would be perfect.

  • Nomographs for Parabolic Reflector Antennas

    Rasto - Congratuliations! I think it is a great work.
    I just don't understand Example 2. Why do we have to convert the SA to a PF-dish and design the feed for that converted f/D?
    The result in example 2 with 10 turns doesn't seem correct as other literature is proposing 5 turns for a offset dish with f/D = 0,65.
    What is the reason for converting to PF?
    73's Gerhard - OE3GBB

  • BLF2425M9 replacement or similar amp?

    It is not a direct replacement, but you should consider to use a BLF7G27LS-90. It is only about € 40,- and good for 18W DATV / 90W CW on 2.4 GHz. I using PCBs out of older router equipment and I did not need to do any snowflakeing. So I could provide a copy of that PCB traces.

  • OBS Studio + PLUTO SDR TX DATV howto?

    For each symbol rate, constellation and FEC there is a maximum possible bitrate of the UDP-stream.
    Using Analysis page I can see green and red dots. There is no explanation, but I think the red ones are dropped. And I think it is a good sign to see zero-packets shown. So fare I studied some examples and used trial and error.
    I would need a good understandable document how to set the main parameters at OBS recording to achieve a certain bitrate. Could someone please point me that document?
    Thanks
    Gerhard

  • What TX amplifier do you plan to use?

    Sorry, I was not thinking to the end as a lambda/w wire would have been around 7,5 cm!!
    It sure is a nice amplifier.
    I have bought a few PCBs of TELRAD amplifiers, from their Breeze Compact 3000 equipment, see #320.
    They do not need any snowflaking and are good for 20W DATV. I am using it as driver, but friends are using them also for linear NB amplifiers. Efficiency is quite bad using the Idq from data sheets, so I will follow your hint and try reduced values.
    73's

    Gerhard