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Zed Zed's Workbench

The 10 Meter Loop Antenna
Loop antennas are a favorite among hams. They are a simple design and offer more gain than a half wave dipole antenna. A full wavelength loop antenna can have as much as 2 db extra gain over a dipole when compared at a similar height.

A loop antenna is usually one full wavelength long but some loop antennas are quite large and may be several wavelengths long. Larger HF loops, such as for use on the 80 or 160 meter bands, are usually mounted horizontally and are often used with an antenna tuner on higher frequencies. Small loops for higher frequencies can be mounted either horizontally or vertically. HF Loop antennas for the 10 through 20 meter bands are small enough that they can be easily suspended vertically with their broadside radiation pattern pointed in a specific direction. The total length of a full wave loop antenna is the same as the driven element for a cubical quad antenna.

Construction
I decided to build a four sided quad loop antenna, mount it vertically and make it horizontally polarized. I used 14 gauge insulated stranded copper wire for the antenna element but you may use either insulated or bare copper antenna wire. With the new radio amateur in mind I calculated the lengths of the antenna to be centered at 28.400 MHz.

10 Meter Vertical Loop Antenna.

The frst step was to measure and cut a piece of wire 37' (11.278 m) long for the antenna element. This allowed allowed an extra 20" for the feed-point connections.

The element is easy to square if you measure and mark where each bend in the wire should be. In marking the wire element the first mark is at 10" (25.4 cm). Measuring from the first mark at 10" the next mark is at 8' 10" (2.692 m). Continue to mark the rest of the sides 8' 10" and you should have 10" of wire left.

The next step is make some insulators for the four corners of the antenna element using 1/2" thick wall PVC pipe. I kept the feed-point simple and only used a piece of PVC pipe for the feed-point connector. I drilled holes in the pipe for the rope and the wire element and simply taped the matching cable to the PVC pipe (as shown in the video).

The spreader in the center of the antenna is also 1/2" PVC pipe. Mine is two sections of PVC pipe with a coupler. One section of PVC pipe is 10' long and the other pipe is long enough to get me the 12' 6" spreader length. I also used two more pipe couplers to connect the spreader to the antenna elements. The holes in the ends of my insulators for the wire element are 1/2" from the end. So I made the spreader 12' 7" long measuring from the ends with the couplers attached. Then I used a Dremel tool to notch out about a 1/2" slit in the couplers so that they would slip over and clear the wire element. A hole was drilled in the center of the spreader for attaching to the rope spreader.

Instead of using additional insulators on the sides of the antenna like I did you may use just the two sections of PVC and a pipe coupler -- or one long section of PVC pipe if you have it. Fit the two sections together with the coupler and drill the holes for the wire element 12' 6" (3.81 m) apart.

The distance from the feed-point of the antenna to the apex is also 12' 6". A rope spreader is used between the top insulator and the bottom (feed-point) insulator.

10 Meter Loop Antenna

 

Video Instructions
Below is a four part video detailing how I built this antenna.
Part 1:The Plan (8:38).
Part 2: Parts and Assembly (12:48).
Part 3: Installation and SWR Check (4:08).
Part 4: Testing the Antenna (3:36).



The wire element is ran through the insulators. The insulators are held in place by using a piece of stiff solid gauge wire about 10" long. One end of the solid gauge wire is wrapped around the wire element then run over the side of the PVC pipe insulator and then again wrapped around the antenna element. A piece of solid gauge wire is also placed through the hole in the center of the spreader and both ends wrapped around the supporting rope spreader.

I used wire rope clips to attach the stranded wire element to the PVC pipe at the feed-point.

Matching the Antenna
The loop antenna will have an impedance of somewhere between 80 and 120 ohms depending on how high the antenna is mounted. To match the near 100 ohm impedance to a 50 ohm feed-point a section of 75 ohm coaxial cable is used. The matching section is one-quarter electrical wavelength long (see diagram for formula).

I used a piece of 75 ohm RG-11 coax. The cable had a foam dielectric and a velocity factor of 78%. After calculating the length I rounded off the measurement to 6' 9" (2.059 m) for the matching section. I cut a piece of cable 7' long. This allowed enough cable for a PL-259 connector on one end and enough cable to separate the center and shield at the other end.

The matching cable is connected to the wire antenna element similar to the same way as connecting a dipole antenna. I ended up trimming off at least 3" of each end of the antenna leads before connecting them to the matching cable. The other end of the matching cable with a PL-259 attached is connected to a section of RG-8 coaxial cable using a double female UHF connector. The antenna can be fed, past the matching section, with any length of 50 ohm coaxial cable.

As far as power handling capability the 14 gauge wire will handle full legal limit. Your real limit is the amount of power that your coaxial cable can handle. The antenna can be matched using smaller RG-59 or RG-6 but if you'd like to use more than a 100 watts and feel comfortable about it then use the RG-11 cable.

Tuning the Antenna
This antenna was built for 28.400 MHz and it came out as calculated. The antenna is very broad-banded and if tuned slightly higher in frequency then it should work the entire 10 meter band. For the General Class operator I would suggest making the antenna a few inches shorter centering the antenna more in the middle of the band. You can use the formulas in the diagram shown on this page to calculate the lengths for the antenna at your desired operating frequency or for use on other bands.

10 Meter Quad Loop Antenna

Parts List

  • 14 gauge stranded copper wire, 37' long.
  • 1/2" thick wall PVC pipe, 13' 7" (for spreader and insulators).
  • RG-11 75 ohm coaxial cable, 7' (foam, 78% VF).
  • 12 or 14 gauge solid copper wire, 4 each about 10" long.
  • 2 each wire rope clips
  • 3 each 1/2" PVC pipe coupler
  • Rope and three dog ties plus upper support.


Safety First!
Please use caution and keep common sense safety rules in mind when installing an antenna. Never install antennas near power lines or in any location that would place people or pets within the near field radiation pattern of an antenna. All users understand and agree that the owner of this web site is not responsible for accidents or other mishaps that may have been caused directly or indirectly as a result of the information published on this web site and/or in any of the video presentations.
 

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