Posts by DH2VA

    You have to be a bit careful about the max. current which USB is capable. With enumeration, this is 5V/500mA (which at 12V is only 200mA) and this is ok. Without enumeration USB will only deliver 100mA and after conversion to 12V, there is not enough power for an LNB. If depends on how the USB device is recognized.

    DL9SEC Du meinst den Zinnmeniskus innen am Rohr zwischen Patch und Reflektor? Das kann die Anpassung beeinflussen... aber die schlecht gelötete SMA Buchse macht das sicher. Das Lotbild vom Reflektor sieht im Bild vom DK1MHW auch ganz gut aus.

    Desweiteren denke ich dass das Kabel (RG-174?) fuer die Frequenz zu schlecht und allgemein viel zu lang ist. Wenn schon lang, dann dick (Ich hab hier Aircell 7 fuer 1m).. oder eben kurz (10cm) und Semi-Rigid (UT-141).

    Wenn da wirklich ein Spalt ist, wird das das Problem sein.. ist bei 2.4 GHz nicht förderlich für die Anpassung. dass /muss/ plan und buendig rundherum *wasserdicht* verloetet werden. Das ist aufgrund der thermischen Masse nicht einfach, aber notwendig.

    double glazed widow, and possibly interference with the lobes from the window's metal frame

    Rather certainly than 'possibly'. I suggest you move the antenna outside and be prepared for a loud signal. Anything (!) else except for air will eat on the 10 GHz downlink. That in particular includes water (rain, fog, heavy clouds, trees).

    I take the liberty to link to Daniel's excellent development of a medium speed data modem, which is tailored to the QO100 NB transponder (rather than using a system developed for HF) . Based on some very good reasoning and design choices, he manages to get 6000 bps through 2.7 kHz of bandwidth while sticking to beacon level power and therefore adhering to the rules of operation.


    https://destevez.net/2019/12/f…nd-data-modem-for-qo-100/


    Bear in mind, this is ongoing work and the higher data framing levels are still missing. It does show however what is technically feasible.

    (Sorry fuer das Englisch oben.. wir sind ja hier im deutschen Teil)

    Das ueblicherweise beim 3D Druck verwendete PLA ist als Ausgangsmaterial nicht geeignet. Diverse Versuche haben bestaetigt, dass eine 3D gedruckte Linse sogar schlechter ist als ein offener Hohlleiter (von einer richtigen Linse ganz zu schweigen). Es koennte am epsilon liegen oder am Tangens-Delta (Verlustfaktor) auf 10 GHz, was ohne umfangreiche Messungen nicht zu eruieren ist. Die einfachste Moeglichkeit ist wie bereits geschrieben eine Linse von einem anderen LNB zu kannibalisieren.

    One should also mention that not only the dielectric constant of the polymer is important (to make the lens act as a lens) but also it's absorption at 10 GHz. Otherwise, the lens will be an attenuator and you could use as well some wet cloth.

    Most negative lens experiences are caused by using improper polymers. Stick with Rexollite or Teflon (which is good to lathe if you do it carefully).

    DD0CW about the observed 24h period: I would guess most of it is doppler. Neither is inclination exactly 0 deg (as of now, it is 0.01 deg), so this results in an apparent North-South movement over 24h. Next is the non-circular orbit, it is slightly elliptic. Perigee is as of today 35789.0 km and Apogee 35799.5 km. So this results in a West-East movement as part of the orbit is slower than perfect and another part is faster than perfect. And on top of this, the different heights result in a up-down movement of course, hi.

    You can actually have it calculated.. just load the TLEs in any satellite tracking program. Take into account, that the beacons are generated on the ground so there is actually the sum of uplink doppler (on 2.4 GHz) plus downlink doppler (on 10.5 GHz).

    pe1hzg No NDA this time: I don't know.. but for commercial transponders, they can actually do geolocation of any uplinking stations to a scary degree of precision.. maybe it's linked to that.

    DD0CW ideal: correct, no doppler.. YES

    radiation pressure is NOT random but has a 24h period, as the sun position relative to the satellite varies during the day. Over the course of one day, sun and moon position relative to earth stay more or less constant and therefore all is dominated by the 24h orbit period of the satellite. One the other hand, sunlight is VERY constant as the tv satellites are almost in constant daylight due to their distance of the orbit to the earth (6 earth radii) and the tilt of 23.5 deg of the equatorial plane to the ecliptic plane. Only around start of spring and fall when the intersection of both planes is aligned with the sun-earth direction the satellites have a some eclipse time. So rest assured, the satellite internal temperature is rather constant and on top of that the transponder LO is actually very stable. Cannot say more unfortunately :)

    DD0CW any earth orbit is far from ideal: perturbation from the moon and sun, radiation pressure from the sun and non-spherical gravitational field of the earth itself (not a round sphere but more a pear). That is why any satellite operator has to correct the orbit every 2 weeks or so with tiny corrections to stay in it's designed orbital position. I think a 50 km box is the allowed space as staying too precise on a given spot is just too expensive in terms of fuel. And that is why a tiny amount of orbital wiggle around the perfect position is allowed. The level of doppler is usually not noticable (DVB-S2 couldn't care less) and therefore not an issue for commercial operators.

    TLDR: having the possibility to use a high gain antenna on the gateway compared to QO-100 global beam compensates for the 20dB more path loss. It will be +- identical in terms of ground equipment.. more details to follow in one of the next journals :)