Dr. Ulrich Rohde: Electrically Short Antennas

Discussion in 'Amateur Radio News' started by AB4OJ, Dec 24, 2020.

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  1. IK4EWX

    IK4EWX Ham Member QRZ Page

    Thanks to Dr. Rohde and SM0AOM.
    It's always ultra interesting to read dr. Rohde on HF receivers.
    And now with this wide diffusion of SDR receivers and transceivers we need really know if they will work well in a new solar maximum in 5 years.
    I am the satisfied enought owner of an Elecraft K3S, with an analogue front end before the sdr, and dont thing for now to change my rig for a pure SDR. I will wait and see/listen...
    Dr. Rohde, it would be a great thing an amateur radio transceiver from Rohde Schwartz, could we dream about it? ;)
    73 and hny, Ian IK4EWX
    KR3DX, N0TZU and PY2RAF like this.
  2. N1UL

    N1UL QRZ Lifetime Member #303 Platinum Subscriber Life Member QRZ Page

    If I am allowed I would like to point out that some of the A/D preamplifier are not linear, reducing the gain may shift the distortion to the preamp, see Dualgate FETS , very pronounced.

    I really wanted to touch the antenna issues here and not slide in a different topic as there is no very complete publications on active antennas.

    I have a recent RX book with McGraw Hill that will guide you through the RX options.

    73 de Ulrich
    KO4LZ, KR3DX, N0TZU and 1 other person like this.
  3. N1UL

    N1UL QRZ Lifetime Member #303 Platinum Subscriber Life Member QRZ Page

    interesting topic. Collins burned their fingers with such a project. The R&S tactical radios use hi rel components, too expensive for the ham market.
    My XK 2100 L is now used for 25 years trouble free but without a panoramic display the hams wouldn’t want it. Great transceiver though.
    For QRP I use the M3TR, the 705 was not on the market then
    Thanks, Ulrich
  4. N1UL

    N1UL QRZ Lifetime Member #303 Platinum Subscriber Life Member QRZ Page


    Here you find almost all the answers....
    Have fun
    DM2VV and KO4LZ like this.
  5. K3MEJ

    K3MEJ Ham Member QRZ Page

    He didn't ask for apology!
  6. K6CLS

    K6CLS Ham Member QRZ Page

  7. AB4OJ

    AB4OJ Ham Member QRZ Page

    WD4ELG, KR3DX, W0PV and 1 other person like this.
  8. AK3Y

    AK3Y XML Subscriber QRZ Page

    Happy holidays, Dr. Rohde. Always nice to work you on the bands. Best 73, Bob AK3Y
  9. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    Very interesting article. Thanks for that, Dr. Rohde. I have been wanting to build an active antenna for a long time, there are a lot of designs to be found on the internet. But reading this, I begin to think that none of the designs I have seen to far, live up to the requirements depicted in this document. A supply voltage of 50V to reach the required IP3 levels.. wow. I wonder if any designs are available in the 'public domain' that do meets these requirements. I'd certainly be interested in one to build.
    Last edited: Dec 26, 2020
  10. N1UL

    N1UL QRZ Lifetime Member #303 Platinum Subscriber Life Member QRZ Page

    Good morning,

    on a battleship with both aktive transmitters and receivers this dynamic range is a necessity and only since LD-MOS transistors are available and GaN Transistors it is possible to build such systems.
    With no co-site operation most of the 24 V aktive Antennas are ok.

    I am more afraid what will happen if the sun activity will be back full force.

    The big mistake in selecting radios happens if the decision is price driven and not performance driven and the system must operate under high electric field field conditions. This to a high extends applies to a contest station.
    Tough choices

    Take a look at VE2AED’s Station or website. Thanks amongst the best well thought out places.
    Last edited: Dec 26, 2020
    KR3DX likes this.

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