• Interestingly, can you also record and display the characteristic Z impedance for the course of the VSWR? In the short test setup, there is no compulsion to 50 Ohm ...

  • Reference level is -1dB (power is 0 dBm), noise floor is around -60, reset with sweeper head.

    New measurement is -25.75 dBm ..... consider that the propeller illuminates an 80x74 offset dish but it is inside the house with the possible reflections ..... this allows me the length of the cables.

    Probable not precise, I'm new in the measures.

    I wanted to pay attention to the problem of the N connector to which to connect the coaxial power cable, which is not practical in the field.

  • IW9EZO said "Probable not precise, I'm new in the measures."


    OK, taking the risk I'm telling nothing new, perhaps a 'short cut' advise (assuming the directional coupler is ok):


    - Leave sweep output on 0 dBm (1 mW)

    - Disconnect the directional coupler from the antenna

    - Place a proper 50Ω load as 'antenna'

    - Measure the response at 2400 MHz

    (if it's a good 50Ω load you should see a (very) low response)


    - Disconnect the load

    - Measure the response at 2400 MHz

    (should be maximum because all power is reflected)


    (normally one should also make a short, but I leave that out ; -)


    Now you have the difference between an 'ideal' 50Ω load and no load.


    - Connect the antenna and measure the level at 2400 MHz.


    The RL Is the difference between the level of the 'open situation' and the level you measure with the helix.


    To see if there is a 'dip' try to increase the span to e.g. 1000 MHz

  • Another helix feed. Design by DJ4ZC, CAD and construction by DH2VA and final alignment by DL5MLO. If enough people believe, that the construction is compatible with hamradio, we could do another journal article..



  • G8HAJ You're welcome!


    However, to check if my memory was right I googled my eyes out. Nothing found. No IARU hits etc.


    Then I phoned some (prominent!) EME-ers and asked them if they could confirm whether the EME-uplink is RHCP. No answer ... (?) However, one person remembered that in the W2IMU EME-newsletters (looong time ago) there was a short article concerning which polarisation to use. With this information I scanned the archives. The result is ... phew ... my memory was right.


    Proof below:



    Edit: I also found the source: IARU R1 VHF Handbook:


  • PA3FYM


    The advice is always valid, I admit to be new in the measures, but with some examples and some suggestions and 'always more education'.

    I made a measurement directly on the sweep (and not through the blue cable Suhner you saw in the picture), with coupler direct output I -20dB, while if I put a load at 50 ohms (up to 10 ghz 10W), I -33 dB .

    Soon I will have a reflectometric bridge of the Wiltron 98A50, so I will have a way to make more reliable RL measurements.

    Slowly we assume experience.

    Greetings de________Maurizio

  • I0LYL

    grazie Lucio, ma usavo gia' un'antenna a elica solo in RX x AO-40 ai tempi, non sono nuovo a questi temi e il sito e stravecchio, anche se con nozioni utili, cmq cercavo o meglio cerco ancora info per le PATCH antenna.

    Cmq TNX....

    73 de______maurizio

    ero settato sulle eliche e ti ho dato l primo link utile.:)

    Parti da qui e vedi se ti è utile.

    Es'hail-2 Transverter

  • 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.

  • No, not connected to GND. Matching is done with a ¼λ transmission line per usual or a contraption like in the picture ; -) I would advise to crop the corners of the copper fane at the center of the connector.


    Zhelix = ca. 120Ω, so ¼λ Ztl = 77.5Ω. Or you can match with a LC network:



  • As mentioned, the aluminum plane is close to the helix but not touching it and serves as a matching element together with the coppler fane soldered to the center conductor of the N socket. Not fully optimized (you are looking at the engineering model so to speak), we have four 'flight models' which are nicer looking, fully tuned up and distributed to the involved persons. If I understood DL5MLO correct, return loss at 2.4 GHz is in excess of 20 dB.

  • Actually it is a good idea to make some connection between center and ground, e.g. a 0.3-0.5mm wire of about 1/4 wavelength (3.25cm) wound in a couple of turns like 3-4mm dia.

    This serves as a short-circuit for static charge e.g. when you touch the helix without grounding yourself first.

  • As mentioned, the aluminum plane is close to the helix but not touching it and serves as a matching element together with the coppler fane soldered to the center conductor of the N socket.

    I see the aluminium plane and the principle of matching, but not "the coppler fane soldered to the center conductor of the N socket.". Hmm... do I miss something or do I need new glasses ? ;)