Moebius loop antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KX4O, May 3, 2020.

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  1. KX4O

    KX4O Ham Member QRZ Page

    Anyone have much experience with the Moebius Loop?

    I just purchased the YouLoop from Airspy and have to say I'm impressed.

    Here it is in a completely isolated system including OpenWebRX running on the battery powered R-Pi.

    Here is the local LF beacon 30 miles south of here from inside my home with much less noise than other solutions...


    Seems promising... not terribly sensitive, but certainly workable for many situations.

    What are other folks' experiences?
  2. WA7F

    WA7F Premium Subscriber QRZ Page

    Was the blue masking tape included in the kit?
    WN1MB likes this.
  3. KX4O

    KX4O Ham Member QRZ Page

    Haha... well nope, but we have plenty of it around from painting projects and makes for good temporary assembly. At least the tape matches the coaxial cable color.
    WA7F likes this.
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    What makes it a Moebius?
  5. KX4O

    KX4O Ham Member QRZ Page

    I think at a minimum the swapping of conductors at the top as portrayed by this 1964 mention of it (spelling a bit different, not sure what is correct)...
    I did test the little SMA to SMA box at the top of the Airspy product and it does swap shield-for-center from left to right and back just like this figure proports. The nulls in this antenna topology are not a surprise, but I guess I was pleased how deep and angularly crisp the nulls are. The lack of noise to signal is surreal, but it might take some time to turn observational excitement into real measurements.

    I'm embarrassed to say I'd never heard of this till now, but my colleagues in the antenna industry were quick to educate me.
  6. AK5B

    AK5B Ham Member QRZ Page

  7. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    So it’s a two turn loop, and it seems the electrostatic balance is no longer there since the split shield is deliberately one turn of the loop. I’m not seeing what makes it different than just two turns of wire?
    KK4NSF likes this.
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    No, it is a single turn loop made out of coax with the gap at the top, with a clever way of bringing the differential voltage developed across the gap to the bottom of the loop by using the inner conductor of the coax to accomplish that.

    Additionally, the capacitance between the coax center conductor and the inside of the coax shield appears directly across the gap, so if you were to "tune" that loop to resonance (like you would an STL with a vaccum variable cap across the gap), the coax capacitance of each half is in parallel first with itself, and then subtracts from the require tuning capacitance that would otherwise be only in the VVC, and lets you mount the tuning capacitor at bottom of the loop to reduce the mass at the top of the loop.

    I read that Carl E. Baum paper a long time ago, and concluded he did not understand his own invention....

    Attached is an unpublished analysis of the Moebius loop I wrote for myself, thinking that I would publish a paper about it some day...

    Attached Files:

    Last edited: May 3, 2020
    K0UO and N0TZU like this.
  9. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks for the explanation, the loop is actually quite clever. Your implementation was well done.

    Did you find the source of RFI you made it for?
    Last edited: May 3, 2020
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Yes, my neighbor's #$%@& Chinese roof-top grid-tie solar system.

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