Dr. Ulrich Rohde: Electrically Short Antennas

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

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  1. AB4OJ

    AB4OJ Ham Member QRZ Page

    At his request and on his behalf, I am posting an article by my friend Dr. Ulrich Rohde entitled "Electrically Short Antennas". The co-authors for this article are Magdalena Salazar-Palma and Tapan K. Sarkar.

    73, Adam VA7OJ/AB4OJ Antennahouse2.JPG
     

    Attached Files:

    W2QA, KA9P, K3BR and 15 others like this.
  2. WO1B

    WO1B Premium Subscriber QRZ Page

    As the Dr. seems to be a lifelong member of this site, why did he not post this himself? I smell something fishy here.....
     
    N7KO likes this.
  3. N1UL

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

    The fishy part is that goofed to load it up with a introduction picture so I asked for help rather then make a mistake.
    Is this considered disorderly conduct ?
    I hop that explains it.
    73 de Ulrich, N1UL
     
    WX1J, K4ZH, WA2LXB and 26 others like this.
  4. N1IPU

    N1IPU Premium Subscriber QRZ Page

    Thanks, Good stuff as always. I like QRZ for this and not for "look at me videos" At some point were going to really miss having true Elmers here.
     
    TI3IES, N0TZU, W2CPD and 3 others like this.
  5. WO1B

    WO1B Premium Subscriber QRZ Page

    No apology will be offered considering the amount of effort hackers go to obtaining our information it makes good sense to be suspicious and let's face it, a paper that says its created by a member but posted by another is certainly suspicious. Maybe the better option was to assist the author with posting it under his own identification? All users should be very careful in downloading or opening files (yes including .pdf formated documents] as they may contain malware and other unwanted items.
     
    KT5OT, G1HYD, WZ4K and 1 other person like this.
  6. KQ4EL

    KQ4EL Premium Subscriber QRZ Page

    Thank you Dr. Rohde, and happy holidays.
     
    AJ6KZ likes this.
  7. N1UL

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

    Thanks and likewise happy holidays, here is a screenshot from a monitoring receiver
    F4FC07ED-8BDE-4ED6-BE1C-E03E4BE723CF.jpeg

    Pretty good up to 21 MHz, RX 2 MHz to 22 MHz display using an active antenna; 73 de Ulrich N1UL
     
    W2ZF, KO4LZ, NR5TX and 4 others like this.
  8. K5SOP

    K5SOP Ham Member QRZ Page

    Excellent paper, very informative. Merry Christmas to all.
     
    KR3DX likes this.
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    A very interesting paper and presentation.

    It highlights the difficult design considerations which especially designers of co-located systems on small platforms face.

    Former associate Emelie Agnedal wrote a paper "System requirements for co-located equipment on small platforms and cost-effective measures to reduce interference" which was presented at the Nordic HF Conference in 2o13 where many of the questions were addressed.

    Finally, recall these almost 45 year old spectrum plots?

    There certainly is a profound difference in HF spectrum occupancy levels between now and "yesteryear".

    upload_2020-12-25_16-37-20.png

    73/
    Karl-Arne
    SM0AOM
     
    KA9P, N0TZU, KO4LZ and 2 others like this.
  10. N1UL

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

    Good morning from the USA, I remember this paper very well. This was measured in the USA and it’s equivalent in Europe was about 15 to 20 dB louder, European Broadcast Stations and “Propaganda “ stations including the Voice of America. Most ham radio stations (RX) on 7 MHz in Europe were totally overloaded and I introduced the PIN diode Attenuator and replaced the Si switching diodes.
    To a degree i am afraid that when the sun wakes up again, the A/D converters of the SDRs will be totally overwhelmed without an adaptive PIN diode based attenuator and it’s AGC system. This complex system will not be trivial and expensive.
    My active antenna saw already 60 dBuV around 9 MHz. European broadcast stations.
    There is more to a good receiver then selectivity and sensitivity!
    73 de Ulrich
     
    N0TZU, KR3DX, NR5TX and 8 others like this.

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