Welche Rundstrahlantenne für VHF-Empfang von Satelliten

  • Moin

    Ich verwende für 70cm die passende Version, für 2m jedoch auch die 137 MHz Version. Der Abstand des Reflektors ist veränderbar. Somit geht es noch einigermaßen im 2m Band.

    Sendeseitig nutze ich sie im 2m Band selten, manchmal auf dem SO-50 (was funktioniert). Die wenigsten LEO habe hier ihren Uplink. Leistung an der Antenne max 20Watt.

    Empfangsseitig kein Problem. Selbst der AO-7 ist zu hören. Sendeseitig kann ich wie schon beschrieben mit der 70cm Version nahezu alle LEO ansprechen, welche im 70cm Bereich ihren Uplink haben. Selbst AO7 geht manchmal.

  • Ich habe vom Stanislav Antwort bekommen.

    Die 137 MHz Version verträgt maximal 5 Watt. Er hat die 2m AFU Version nicht mehr angeboten, weil keine Nachfrage da war. In den letzten 2 Wochen hat aber die Nachfrage sehr stark zugenommen. Er wird die Antenne produzieren und in der nächste Woche wieder online stellen.

    Die 2m AFU Version besitzt eine N-Buchse. Der Balun wird aus RG11 sein und wird 50 Watt vertragen.

    Er schrieb mir, dass er sich meldet sobal die Antenne online ist.

  • I have the experience, but not the ability to read German. My company Timestep, once made one of the most expensive QFH's for Super Yachts and low cost crossed dipoles for amateurs.


    Most antennas of all these types do not work properly.


    A QHF with the correct phasing does work and has no nulls or polarisation changes. However most home brew QFH's do not work due to construction issues.


    Peter, what exactly is your question and application ?


    Regards Dave

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Hi Dave,


    just experimenting with different kinds of Omni directional antennas optimized for LEO satellites and getting some interesting results ;-)

    I already started with LEO's long time ago, OSCAR-6 and OSCAR-7, etc., UoSAT OSCAR-9, UO-11 DCE Gateway and PACSAT's, but at that time I was already using high gain antennas with AZ/EL rotator. When OSCAR-40 stopped working, I removed all my 2m/70cm antennas when they got damaged in a storm :huh: Also somehow lost interest in LEO's and did not put something up again..


    When I was already working on QO-100/P4-A and planning my antenna for it, an LEO OSCAR satellite opportunity came up (which I can not describe here for usual reasons). I wanted to find out which kind of antenna could be a good one for simple ground stations.. So when I installed my QO-100 antennas, it was a good chance to put something up again to see how it goes and also to try different antenna types.. many reports on these antennas are contradictory and there is no clear overview.


    There are lot of things to take into consideration, which you already know..

    • LEO satellites spent most of the time at mid and lower elevation, that's where you want to have antenna gain!
    • Overhead passes are seldom and quick when overhead, i.e. only little time spent there and slant range is shorter overhead, so this should be compensated with less antenna gain.. no antenna gain needed here...
    • And indeed you want to have it circular polarized with a "kidney" shaped pattern..

    Turnstile does have a lot of nulls and not such a nice pattern as QFH, but QFH antenna pattern is not so good at lower elevations and wasting too much gain in Z direction.

    Indeed, both antennas can be "tweaked", but you need an antenna range to find the optimal pattern. ;-)

    I use the FOX Cubesats and the Fox Telemetry Analysis tool, as it allows to print nicely the received signals strength plotted in AZ/EL as mentioned earlier in this threat.

    As you can see in an earlier post here, I was running the TA-1 antenna for 1 year. It works nicely at lower elevations, but does have some bad nulls at higher elevations.

    I have exchanged it now with an Eggbeater and will run the same experiment again over the coming winter ;-) There is also an interesting article from Jerry K5OE about his Eggbeater II which was very popular in the early time of PACSAT's and LEO's.. not sure why it got almost forgotten..


    73s Peter

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • OK, if you look into the design of QFH's you can optimise them. On our 137Mhz weather satellite version we deliberately cut off the first and last 10 degrees to kill terrestrial man-made noise. This gave us maximum s/n over the majority of the pass which is what we wanted.


    It is going to be a challenge to get horizon to horizon gain and circularity. There are antenna design books somewhere here, I'll try to look them out ?


    BTW I remember UoSAT well, we had a license from James Miller G3RUH for his data correlator and we supplied complete receivers to the Surrey Ground Station. Those were the days ! And unexpectedly I met James at the RSGB Convention a couple of weeks ago, the first time since 35 years....................

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Ideally yes, practically no. The isoflux antenna is designed to provide a uniform flux on the visible earth beneath a satellite taking account of distance. Putting one on the earth would give the characteristics asked about - well almost as they don't radiate towards the horizon but from about 20 degrees and up. The concept remains and not seeing the horizon is often good for noise rejection.


    This https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6239565 is a nice paper and proposing a meta-surface made from small patches. This sort of thing is perhaps too complex for amateur use, but it's something that could be made for satellites.


    A long quadrifilar helix antenna is possibly a good option.


    Mike

  • Hi

    ein kurzer Einschub zu den Trunstile von Ebay. Der Verkäufer hatte mir folgende Info zukommen lassen (deckt sich mit dem, was DL2NED schon auch erfahren hatte):



    the 137Mhz version could be used on 2m since it is broadband and decent SWR can be reached, However, antenna can take little power due to internal balun, and 5w rated.


    The regular 2m turnstile use different much ´´heavier´´ balun made from RG11 which can tolerate 50w .


    The antennas are scheduled to be on the sale this working week. We planned only couple of pieces but will reconsider and bring more items on sale.


    Die "5 Watt 137 MHz" Version habe ich jedoch schon mehrfach ohne Probleme mit 20 Watt belasten können. Die Angaben scheinen somit konservativ.

  • well almost as they don't radiate towards the horizon but from about 20 degrees and up. The concept remains and not seeing the horizon is often good for noise rejection.


    Mike

    But that is exactly what the OP did not want, and worse than my QFH suggestion ??

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Yes - except it depends on the way the antenna is designed. Isoflux is a concept of a radiation pattern, not a single antenna. The designs I have seen are all for satellites but there is no reason at all why one can't be designed one with a lower radiation angle, except it usually needs simulation software that's not available at amateur prices.


    There is also the question of why circular polarisation is required. If the satellite is circular that's understandable but quite possibly it's linear but of unknown polarisation angle so the axial ratio isn't as important.


    SDR receivers are cheap so it's sometimes worth just having several antennas looking in different directions each driving it's own receiver. I have done this in Gnuradio for other applications.


    The QFH you mentioned is a simple to make antenna and this is a nice summary: http://orbanmicrowave.com/wp-c…drifilarHelixAntennas.pdf


    Mike

  • Alexandru OZ9AEC recently twitters the following polar plot from OZ7SAT on telemetry frames received from LEO satellites:He asked: "Can you explain why most telemetry is received at elevations between 10° and 40° ?" (this is the yellow and red area in the plot)


    If you read carefully what I have written before, you will quickly find out why and how an optimal antenna pattern should look like... additionally taking the slant range into account :-)


    Indeed the answer is, that the LEO's will spent most of the time below 40° Elevation...

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG