Skywire Loop Antenna aka W0MHS Loop Skywire aka Full Wave Loop Antenna aka Magnetic Loop Antenna Observations by Jason Buchanan - N1SU

Update:

Some call it a Skywire Loop Antenna, some call it a W0MHS Loop Skywire Antenna, nowadays it's called a Full Wave Loop Antenna but it still is a force to be reckoned with. In the first couple hours of having it up I was able to hear stations I could not hear before.

The skywire loop is an excellent antenna - they can be a bit of work to get up in the air if you have a lot of obstacles (trees, xyl, etc.) but it is worth it.

What's the right length?

The length of a loop best suited for operation on 160 meters is too short for use on the higher bands. The optimal choice is to cut the loop for resonance on the highest band you plan to use, however it becomes difficult to use a giant 160 meter loop on 10 meters - your feedline length must not be a fractional wavelength of the band you want to use or else you'll wind up using your feedline as the radiator!

If you plan to use the loop for 160 meters 99% of the time then cut it for 160 meters @ 544' - but be prepared for difficulty and reduced performance above 7MHz.

I recommend a different loop for use on 20-10 meters if those are your favorite bands, mostly because it's easier to put up 71 feet of wire (14MHz) with only 18 feet per side. It's also easier to make a 23' diameter loop for 20 meters more circular instead of square shaped. Remember, the ideal loop is a perfect circle - it's not too hard to make an 8-sided loop for 20 meters using PVC pipe and some dacron rope to hold it rigid.

Formula for length of full wave loop

• 544' is comfortably resonant at 1.847kHz, 3.694kHz, 7.389kHz, 14.779kHz and 29.558kHz. Not an optimal length.
• 560' is comfortably resonant at 1.794kHz, 3.589kHz, 7.178kHz, 14.357kHz and 28.714kHz. Not an optimal length.
• 565' is comfortably resonant at 1.778kHz, 3.557kHz, 7.115kHz, 14.230kHz and 28.460kHz. Still a little short.
• 574' is comfortably resonant at 1.750kHz, 3.5kHz, 7.00kHz, 14.000kHz and 28.000kHz. My personal preference.

Performance Observations

Polarity of the loop shouldn't matter but sometimes it does. The difference in polarity can be heard as some stations being much louder than others when the polarity is changed - i'm guessing this is due to cancellation of signals as received by the different length of the sides of my loop. A circular loop would reduce these effects.

I have an old DPDT copper knife switch that I use to switch the polarity of the 160 meter loop. My experiments with smaller loops, 20 meter loop for example, shows that the polarity plays very little role.

Performance is exceptional and rarely is beaten by a dipole at the same height.

Feedpoint location is important - it's preferable to have the feedpoint on the north side of the loop (or a side that faces a part of the world where there is little DX), especially if your loop is square. My loop's performance was increased by moving the feedpoint to the north side; stations to the south were easier to hear.

Corner feedpoint locations of square loops increase gain in the direction of the opposite corner. A loop fed in the southwest corner will have a few dB (3dB or more) gain favoring the northeast corner. The loop really, really cuts the mustard on 160, 80 and 40 meters compared to a dipole at the same height. It works just fine and dandy on 20 meters as well but I'd rather have a dedicated 20 meter loop for 20 through 10 meters. I had a separate loop for 20-10 and it was far easier to put up and maintain (a lot less wire to be targeted by nearby falling tree limbs).

Other observations

• Signal reports are usually equivalent or better with the loop than my 20 or 40 meter dipoles at 38-40 feet.
• QSB seems to be less of a problem with the loop than the dipole - the fades aren't as deep and sometimes not there at all while the dipole could be horrible.
• The loop is a little quieter than the dipole, especially on the lower bands.
• My experience so far has been that the computerized models of loops are over-optimistic compared to real operation in the field. You can get a rough idea with modelling software but that software doesn't take into account how much the wire droops from the corners to the middle of each side, etc. The exception to this is corner-fed loops, they do have a strong lobe as the models predict.

Progress

11-Nov-06: Another 3 hours spent cutting more limbs and branches I didn't see near the end of the previous day.

21-Nov-06: I worked HC8N quite easily on 30 meters with 100 watts - big pileup but easy to work.

Winter 2007 - 544' to short - added another 20' - 15 meters is much easier to tune now

Spring 2008 - wire broke - my pulleys are too small, I should have used a 3" pulley at each corner. Added more wire - 574' is a great length.

Common Misconceptions and Myths