Having played with a Loop, I made one octagonal about 64 inches across, and mounted it vertical or perpendicular to the ground, I observed sharp nulls through the center of the loop. Additionally, I took a 4 or 7 watt flurescent bulb and while transmitting (low Power) ran the bulb from top to bottom and found that about ( reference feed point at the bottom, 6 o'clock position, im calling it zero degrees and tuning cap at the top, im calling 180 degrees or 12 o'clock position) 60 degrees about at 4pm point the bulb started to glow and was brightest at about 100 degrees 2:30 position and dropped back to dim to extinguished at 180 degrees. The loop was made for 20 and 40 meter operation. It is physically too large for 15 meter operation. When I made a tuning cap to resonate it on 80 meters knowing the efficiency would be maybe 3 percent, the only place the bulb lit was near the top with no glow from zero degrees 6 o'clock to 150 degrees or about 1-130 o'clock positions. All NVIS on 80 meters with a small loop. This was reinforced by its behavior on 20 and 40 meters. 40 had about a 5 or 10 degree higher angle of radiation over the 20 which was more evenly current distribution on the loop, with the main (brightest) lobe lower in the loop.
So when we look at loops and directionality, the frequency of a multi band loop does change the radiation pattern. The bigger the loop for the band the more evenly distributed current was distributed along the loop. Up until the physical size of the loop does not follow the loop formula and gets too big to be considered a magnetic radiator. On 40 it radiated brightly at the 3 to 4 oclock positions but on 20meters, the current was more evenly spaced from about 430 to 1 oclock positions. On 20 it was brightest at about 245 positions. Maybe this is not scientific but my believe is that, this is demonstrating the angle of the lobes coming off the loop. It seems that it radiated well in the 20 to 30 degree take off angles on 20 and 40 meters with 40 meters being a bit higher more like 25 to 45 degree take off angles. Having this loop in my dining room on the floor of my house over a 3 foot crawlspace, I was able to work Europe repeatedly during the afternoon hours. I did this more than one time months apart. It was not a propagation fluke. Rig was 75 watts CW from a Yeasu FT 450d. I use it as my test rig. I built the loop to prove that they do not work....yet again I was proven wrong. My loop was made out of 1.5 inch by .25 inch thick Radiused edged aluminum bar. I got this from onlinemetals.com. I used radiused bar because RF does not flow around corners well. And, structurally, it was self supporting with a small bracket for a stand. And, it is just easier to work with flat stuff rather than round stock. By using the calculation on the web it performed identical to a 1.5inch copper tube. It was cheaper and much easier to work with. Additionally, I made it so it could be disassembled, yes I know the problem with resistance, don't go there, after all it is a compromise antenna and I was building it for portability and sturdiness. This loop really performed beyond my expectation. Was it better than a full sized vertical or a trap vertical with radials...Oh hell no, but I did make good contacts and even checked into many 40 meter and 20 meter nets from having it inside my house on the floor of my living room. I positioned the plane of the loop east west and was easily able to work both coasts and into Europe. Most of my contacts on it were on CW. See the attachment of it in my living room. When I rotated the loop 90 degrees on the axis the signals dropped from 2 to 6 S units, mainly depending on the distance from my location. The closer in the less drop. I attributed this to the NVIS component of the radiation (the 1 o'clock radiating area). [ATTACHMENT TOO LARGE FOR FORUM STANDARDS, IF YOU WANT A PIC I WILL GLADLY FORWARD IT.] Well this is my experience with my loop and here is a picture of the loop in its final configuration (see attachment) and no I don't want to be flamed about the construction but it works and with some fine emery paper and no-al-ox on the joints. It has a very sharp resonance and narrow band width of maybe 5kc 2to1. After that, it ,the SWR climbs like a wall > 25 to 1 But even though the SWR may be high off the sharp resonance transmit frequency, it still was a good rx antenna broad banded 100khz with very low noise. I can not say it was immune to but, it did not pick up electrical noise like the full sized vertical and the noise floor was lower than the typical vertical antenna. I have a full sized 40 and 20 meter vertical with 60 radials to compare it to and it does not get the same sig reports as that vertical but I did not expect it to. On occasion, with a preamp for rx (dx engineering one) copy was better on some stations over my outside vertical---only because of the reduced noise floor. It was a fun project and I really enjoyed the construction. They are not a miracle antenna but any antenna is better than no antenna and for many this may be the only option to be able to operate. Hell when I get moved into a retirement home, I will use it for a clothes rack and transmit on it when no one is looking. Since digital, PSK**, would be an ideal use for a loop as you don't need much power for the computer to do the heavy lifting. QRP signals are still good enough for computer ears, but not necessarily for ours.. LOL. In the end, it is another example of "QRP Works." Good luck with your Loops Vy 73, Morgan Bailey NJ8M ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
