Posts by DL5RDI

  • RHCP...

    Hallo,


    ich denke die Wendel ist nicht mit Masse verbunden.

    Sie geht vom Mittel-Pin des Steckers (via Kupferfahne) direkt an einem Masseblech (mit wenigen mm Abstand -> Anpassung) vorbei und dann an dem nicht leitenden (Kunstsoff ?) "Skelett" nach oben.

    Also kein Kontakt zur Masse - oder habe ich etwas übersehen ?


    Servus, vy73 Johannes


    Sorry I forgot that 's the english speaking part - we were discussing if there is a GND-connection of the Helix - I don't think so.

  • RHCP...

    Hello,


    I also already built a helix antenna myself for use in an offset dish, But the weatherproof - out of the box - solution from WINKLER for an affordable price cought also my attention. I also ordered one which is specially tuned to 2400 MHz (not 2450) (you can get this without additional cost, when you write an Email mentioning this). There is probably no difference but it "feels" better :-).

    Maybe WINKLER could also produce a customized 7 turn helix-feed for 0,7f/d offset dishes.


    73 de Johannes

  • Wie QRV werden?

    Hello,


    just a very trivial remark to save costs in becoming QRV via P4A.


    RF-specialists: please stop reading here. ;)


    To save money for expencive 50 Ohm I use cheap 75Ohm Sat-coax not only for receive, but also for the connection of my 2m or 70cm TX with my upconverter. You just have to take a lenth of multiples of 1/2 lambda (keep in minde the shortening factor of your cable - if you don't know then just make try and error). And you should use very good shielded coax (like for reception also; e.g. 130dB four layer shield).

    Thus you have no transformation and 50 Ohm in and out. The signal loss is not significant.

    I have 20m to my antennas and an SWR of 1:1 with costs of less then 4 Euro (even RG58 is much more expensive).


    73 de Johannes


    P.s. some may think : Even my grandmother knew it

    My answer: But she didn't publish it :)

  • Smallest Dish Size

    Hello Iain,


    it's a bit off topic - but do you really have to care about a few adapters or the cable length ? The LNB converts the 10GHz Signal to the IF and has here a very high signal level. In "normal" conditions (e.g up to 20m coax and a few adapters) the total signal (even the noise) drops, but in these conditions you do not really have a change in S/N. Or am I wrong ?


    If someone knows better then I appreciate every comment - please with explanation. (I'm a physician and not a HF-engeneer :) ).


    73 de Johannes

  • LNB Skew on Cassegrain

    Hello Rene,


    you are right with the LNB even in the cassegrain antenna counterclockwise... I disregarded that you also turn the LNB 180° (looking towards the dish in "normal" configuration, but turned 180° around its vertical axis and then pointing towards the "sky" in cassegrin antenna.)

    Thus the polarisation is of course "mirrored" by every reflector, but the LNB orienttation is in both cases counter clockwise because of the additional "mirroring" of the LNB.


    73 de Johannes, DL5RDI

  • Es'hail-2 beacon frequency (non-amateur)

    PY1SAN:

    Nice duoband-solution. The RX seems to work very well.

    Did you test the Helix feed (of course NOT in direction to 26E ;-)) ) - is there interference of the TX-signal on 2,4 GHZ with the reception of the LNB ? What about the loss in gain because of the helix-feed is "to close" to the dish and not really in the focus ?


    Any information and data would be appreciated.


    73 de Johannes, DL5RDI


    P.s. thanks to Heiner for posting the Youtube-Video !!

  • LNB Skew on Cassegrain

    Hello,


    is it really the same angle ?

    Each reflector acts as a mirror. When you take porarisation: in a "normal" dish you have a LHCP feed and get (because auf the mirror-effect) RHCP polarisation.

    The skew angle is "part" of the polarisation. If you are standing behind a normal dish with view to the satellite, the LNB has to be turned counter clock wise for all east positioned satellites. But in yor case you have an additional mirror and thus I believe your LNB has to be turned clockwise (seen from the same postion as described above).

    in my QTH (JN58xx) it is a bit more then 13 degree for 26 E. But you can also take the empiric way and tune to a TV transponder on BADR4 (e.g. 11996 SR 27500) - it's the strongest one) and see the change in quality of the signal.


    (For all TV-Sat DXers - Astra is not a "normal" satellite in this way, because SES "tilted" the satellites a bit to have a skwe angle of near to zero in DL - the main viewers).


    73 de Johannes, DL5RDI