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Magnetic loop antenna on the Alps: experiences and issues

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by IU2GLX, May 30, 2017.

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  1. IU2GLX

    IU2GLX Premium Subscriber QRZ Page

    As I am still putting away the tools used to set up my new vertical antenna in Milan (Italy), I am already considering another antenna for my mountain house on the Alps. Cool enough, our apartment sits at 2,000 mt (6,500 ft) and I can't wait to try a dx from up there. As it is very windy and I got very limited space, I was thinking maybe a magnetic loop could be a good choice.

    However, I read that it may suffer cold weather and, as temperature drops below freezing, it will fail to tune until i raises up above 10°C (50°F). I am guessing maybe condensation sometimes ices and ice blocks the motor? But hey!, wouldn't a manufacturer take in consideration this issue?

    So I am asking to OMs in cold countries/regions who own a magnetic loop: have you ever experienced this problem and (if so) how did you solve it?

    From my internet searches, I also noticed that most users chose to mount their loops vertically (often without a rotor), although these antennas are directive. Any thoughts on why not chosing a horizontal polarization? I'd say this would be the best choice for dxing and for reducing the impact of wind...

    I also read about the (well known) MFJ 1786/1788 and the (twice as expensive) Mazzoni Baby/Midi Loop (http://www.wimo.de/ciro_mazzoni_magnetic-loop-antennas_e.html): does anybody have any experience with any of these (or other models, for what matters)? Unfortunately, I do not think I have the manual skills to build one...

    Thank you for sharing your thoughts with a newbee and...

    73 form
    Stefano IU2GLX
     
  2. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    You need to have height above for horizontal mounting. I imagine that most people buy these antennas so that they don't have to mount anything high.

    I am planning on testing horizontal placement more, as I have buildings to work off of. I did try it, somewhat, with my friend's AlexLoop. I noticed a significant drop in noise, but I wasn't sure if that was just lost of good receive, or loss of noise. Not many signals that day. I want to test it again, by suspending it about 7 meters above the roof of my 5 story home building, and see if there is any difference.
     
    NH7RO and KD6RF like this.
  3. NH7RO

    NH7RO Ham Member QRZ Page

    Ciao, Stefano; STLs work best at very low heights above ground when oriented vertically and very high heights above ground when oriented horizontally. When horizontal, they radiate omnidirectionally instead of bidirectionally.

    As for very cold alpine temperatures perhaps a low-wattage 12vdc (marine type) incandescent bulb mounted below the capacitor (and inside a plastic weatherproof enclosure as well) could keep things from freezing up? That's what I'd try.

    Building your own STL is not as hard as many may think and a DIY loop can result in very good performance. Check out the Yahoo Groups like the Mag Loop Group and K8NDS's Helically Loaded Fractional Wave Antenna Group for loads of info and photos.

    Ciao & 73,

    Jeff
     
  4. KK5JY

    KK5JY Premium Subscriber QRZ Page

    The vertical orientation is actually the easiest one to achieve DX angles. As @NH7RO pointed out, DX angles aren't difficult at low heights. If you model some STLs, you'll find that the optimal height above (flat) ground for a vertically-oriented STL is a bit less than 1/4 wavelength as measured at the top of the loop. I have used loops for 80m and 40m that still had good DX response at elevations as low as 15' (about 4.5m, measured at the top of the loop).

    As far as directional, the loop isn't really that directional, when oriented vertically. The azimuth response is somewhat similar to a dipole antenna, with two very wide lobes. The true nulls of the antenna tend to be very sharp, and they tend to only null out signals at very low angles (e.g., up to 2 to 3 degrees). So while the loop isn't omnidirectional like a vertical, there tends to be an azimuth orientation where a fixed installation can work all the desired azimuths and elevations without needing a rotor.
     
    NH7RO likes this.
  5. NH7RO

    NH7RO Ham Member QRZ Page

    Matt; I agree with what you say above---all FB---but why do you always put ampersands in front of callsigns?

    73, Jeff
     
  6. KK5JY

    KK5JY Premium Subscriber QRZ Page

    The '@' turns the callsign into a link. Try clicking on your call above, and you'll see what I mean.
     
  7. NH7RO

    NH7RO Ham Member QRZ Page

    OK, thanks---just curious.
     
  8. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    And FYI, I achieved a 19,000 mile longpath SSB contact, from Korea to IK4GRO in Italy, with just 10w and my friend's Alexloop, on 17m. That was May 4, this month.

    The oddity of that is I was on a 13-story building! The STL was at the very edge of the building, and vertical.

    In that situation, there was also a very long steel ground strap, along the edge, and a building railing, directly below the loop. Have always wondered if those acted as a kind of radial?
     
  9. NH7RO

    NH7RO Ham Member QRZ Page

    Yes, STLs benefit from a few radials underneath. Great contact!
     
  10. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    Radials not connected to anything? Just laying on the ground?
     

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