BaMaTech DuoBand-Feed: receive poor?

  • HI all,

    Hope you can help me solve a problem. I am using a 80 cm offset dish in south of UK.


    With a standard satellite LNB (Visbleware VK4L) I can receive very well, for example the NB beacon shows 38 dB S:N using SDR Console.


    When I use the Bamatech dual feed antenna, my RX side only achieves 28 dB on receive. (All SDR setting remaining same).

    I have experimented moving the focal point +/ a few centimeters seems to make a few dB difference.

    (My up-link seems to work ok - getting S6 reports with 2 Watts).


    I attach photos. Wondering do I need a dielectric lens for the dual feed LNB because I am using offset dish ?

    Or maybe I have a bad LNB from Bamatech?


    Thanks in anticipation.

  • Thanks Heiner,

    My Bamatech POTY is using Opticum LSP-02G LNB indeed marked as linear H / V. So should be Vertical with 12V feed.

  • DB2OS

    Changed the title of the thread from “POTY receive poor - what am I doing wrong?” to “BaMaTech DuoBand-Feed: receive poor?”.
  • G8KWX

    Hi,

    similar observations here.

    Did some experiments with an original LSP-02G and my BaMaTech feed WITH dielectric lens.


    Difference is about 5dB here.


    I think the BaMaTech feed couln't be mounted with optimum focus because of the big reflector of the 2.4GHz feed.


    73, Thorsten

  • Thanks Thorsten, all,


    I see your point about the optimum focus.


    On taking apart two LNBs that work well, the difference to the LSP-02G seems to be the wave guide has a wider aperture about 55mm stepping down to about 20mm presumably a match or somehow related to offset feed point that the 'good' LNB's are designed for. (Pic attached) .


    I now assume that the LSP-02G is meant for center fed dish ?


    Anybody share any light on this.

  • Until now, i am also not happy with my duofeed Bamatech. It has been reportet to me there is as lnb a Opticum LSP-02G in use. I ordered two of them to investigate about the sensitivity, modification etc. Also I like to compare it with other different brand lnb. I opened one of the Opticum without problems and checked the possibility about the modification with a external TCXO.

    First of all I installed the second Opticum LSP-02G to my 85 cm offset dish and carefully pointet it to the QO-100. The result with this lnb has been very bad, it jumped very strong with the frequency. See my screenshot from the SDR console.

  • From all testet lnb this produce the weakest signal compared to the others bevor. Bamatech selected the lnb against wobbling this shows the nr. at the bottom and this lnb was not wobbling. But with this bad sensitivity it will be not possible to use it for good contacts via QO-100. The lnb with the best sensitivity is the GM-201 with clear and strong signals.

    At a other place at this forum we discuss bevor the possibility to change the Opticum LSP-02G but we found no solution how to do it. In the moment I have no ideas how to overcame this problem.

  • I now assume that the LSP-02G is meant for center fed dish ?

    I would say no, i would assume most of the use cases for TV reception are for offset dishes.


    I use a multifeed configuration with the QO-100 feed 2.2° out of focus and the Astra feed about 4.5° out of focus.

    The waveguide at the unmodified LNB seems to be a bit better in a direct comparison.


    The BaMaTech duoband feed is just a compromise, if you want to have a compact, mechanically well solved and good working solution I would say.


    I am currently experimenting to feed the BaMaTech LNB with 24MHz instead of 25MHz. I am curious, if the LNB works better at about 1.1GHz IF. Maybe that's a way to get out the last dB...

  • Finally I install the Bamatech Duo Feed with included Opticum LSP-02G and testet the sensitivity.

    Uuuh, that' really a big difference to the GM-201.


    That's my spectrum at a Kathrein CAS80 with 0dB additional gain of my RTL-SDR...


    Edit:

    Just a note: Feeding the LSP-02G with external reference of 25MHz (from the new Amsat Downconverter) brought nearly 8dB more S/N than with my TCXO modification...

  • Thanks DJ7WL   DL9SEC ,


    Interesting you got 8db better performance by doing crystal lock. I have been using the new feature in SDR Console which allows you to lock the sdr to the beacon, gives good results on all my lnbs. At least for stability. I had assumed that I do not need to do any tcxo mods. Do you agree or is there something else limiting the sensitivity. The phase noise must be really terrible of it hits the sensitivity that much.


    Another thought, has anyone tried mounting a second lnb next to the Bamatech duofeed to get good rx link. Then just use the Baratech for the uplink.


    If that does not work it looks like 2 dishes will be needed 🙄