February 8, 2021

40m Skywire Loop Antenna Experiment

I have been curious about skywire antennas since becoming a ham.  I first learned about skywire antennas initially from a contacts made with hams operating on skywire loop antennas.  Over the years I have received many recommendations to give one a try.

I decided it was high time to build my own homebrew skywire loop antenna with the goal of constructing it from various pieces-parts available in the shack.  There is simply no better way to spend a Sunday than making something in the workshop with the HF transceiver running.

A full wavelength skyloop antenna has a nominal impedance of 120 ohms depending on various factors.  The ideal antenna impedance is 50 ohms which would match a 50 ohm coaxial cable and 50 ohm transceiver.  A skywire antenna would work more efficiently with a 2.5-to-1 balun to transform the antenna impedance to more closely match the 50-ohm coaxial cable.  

A balun is an electrical device that converts between a balanced signal and an unbalanced signal. There are many different types of baluns including those that transform impedances.

Unfortunately, I didn't have a 2-to-1 or 2.5-to-1 balun in the workshop.  I did have a 1-to-1 balun and a box of type-43 ferrite beads.  I decided using a 1-to-1 balun and ferrites would be close enough and help keep common mode currents off my coaxial cable.  I also had an unused coaxial antenna center conductor, a spool of wire, and a few insulators.  These were enough parts to give the 40m skyloop a ago!

A skywire loop antenna is exactly as it sounds a single wire in the shape of a circle (ideally) some other shape such as a square, rectangle, or triangle and suspended horizontally.  To calculate resonance of #18 wire, the following formula can be used:

Length in feet = 1005 / frequency in MHz

For example, at the FT8 40m calling frequency a resonant skywire = 142 ft. = 1005 / 7.074 Mhz

Skywire Loop Antenna Bill of Materials
  • 136 ft of Poly-STEALTH 18 gauge wire from Davis RF
  • qty 11 type-43 ferrite beads 1/2" snap on
  • CE-1 Deluxe Dipole Antenna Center Feed from Spi-Ro Manufacturing
  • 1-to-1 Balun Designs Maxi Choke Balun (5kW) dual core model 1115du
  • qty 3 "dog-bone" type insulators
  • Self-sealing silicon tape
  • 3M electrical tape
  • Stuff - dielectric water proofing filler for coaxial connectors

CE-1 Deluxe Dipole Antenna Center Feed

1-to-1 balun connected with LMR400 with ferrites connected to the antenna center feed 

I used trees to support my skywire loop antenna.  Two of the corners were up around 40ft and the other two were on the low side at around 20 ft.  Not ideal but good enough to tune up and work some DX.  I used floating insulators when hanging the antenna.  Floating insulators allows free movement of the insulators and antenna wire while adjusting the antenna.  It allows provides freedom of movement due to tree sway.

The goal in hanging a skywire loop antenna is to maximize the enclosed area of the antenna.  Given infinite hangers, a circle would yield the maximum enclosed area.  Fortunately, the skywire doesn't require perfection.  A rectangle with four hanging points works very well too.

The Poly-STEALTH antenna wire from Davis RF is wonderful to work with - strong, light, and nearly invisible.  136 ft. of #18 wire weighed only 0.136 lbs. which is much less than my multiband fan dipole.  The insulators and rope weighed more than the entire antenna.

Initial Results

I was delighted to find that I my Kenwood TS-480SAT's build-in antenna tuner would tune the skywire on 40m, 20m, 17m, 15m, 10m, and 6m effortlessly.  This is a great way to begin testing a new antenna - no tuning or trimming.  Next I fired up FT8 and worked 20m and 40m contacts as the grey-line passed on into the evening.  The signal-to-noise ratio seemed improved as compared to my fan-dipole antenna.  I quickly made contacts with stations near and far including:
  • 40m KN4APP, NV - 203 miles
  • 40m AB6ZQ, CA  387 miles
  • 40m KE7JBK, AZ - 597 miles
  • 40m N7DBO, UT - 600 miles
  • 40m KF7UGG, OR - 618 miles
  • 40m K7EAZ, AZ - 694 miles
  • 40m KS7TU, WA - 792 miles
  • 40m KG5ZZB, TX - 1460 miles
  • 20m KB0BRO, MN - 1565 miles
  • 20m W9RF, IL - 1797 miles
  • 20m KH6AN, HI - 2353 miles
  • 40m N3MK, VA - 2527 miles
  • 20m JA9DJX, Japan - 5286 miles
  • 20m LU8DN, Argentina - 6597 miles
  • 20m ZL1IA, New Zealand - 6732 miles
The 40m Skywire experimental antenna was a huge success.  The antenna worked perfectly the first time I tuned it up.  It is remarkable how flexible the antenna is using just a build-in antenna tuner.  No adjustment or fine tuning was required to get on the air on multiple bands.  It also performed very well at the bottom of the sunspot cycle.  Overall, I am pleased with the outcome and would recommend a skywire loop antenna to anyone with suitable supports, a few inexpensive parts, and a Sunday to experiment.  It is a surprisingly good antenna for very little cost.

I am looking forward to trying out the new skywire antenna on 17m, 15m, 10m, and 6m when the bands are open.  I am also looking forward to a future experiment with an 80m skywire loop antenna.

Good DX and 73, NJ2X

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