Home Amateur (Ham) Radio Antenna Building Build an Optimum Spaced 2 Meter Quad
Build an Optimum Spaced 2 Meter Quad PDF Print E-mail
Written by Tim Wray   
Friday, 04 April 2014 14:41

Many years ago back in 2003, I began getting back into Amateur Radio Direction Finding, or "ARDF". Locally, we call it "fox hunting". The local variety is to have one person transmit from public access property, fixed location, once every few minutes. All the "hunters" start from the same location and attempt to triangulate the fox's location based on readings of their signal with directional antennas.

The following is a plan for one of those directional antennas I built at that time. I used the original version of this antenna I built for quite some time, and then rebuilt it a bit sturdier, which unfortunately made it's weight and wind load too high for my comfort for ARDF use.

That said, it makes an AMAZING base station 2m quad. I am planning on building another using PVC or any other light weight materials I can dream up.

Photos of both versions of my original antennas can be seen on this older BWR page.

As the original website I took this from was a Geocities website, and therefore long gone, I managed to find a copy of the page I'd saved, originally published on the "Tech Bench Elmers Amateur Radio Society", KF6GDJ, in the late 1990s. As I can find no other record of it anywhere but on web.archive.org, I am republishing it below in its entireity. It was originally published February 1997.

73 DE KB9SNL

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Two Meter Wavelength
Optimum Spaced Cubical Quad Antenna

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In 1976 at the VHF/UHF Conference in Santa Maria, California, a conversation occurred which discussed the merits of various beam antenna designs. During this discussion the comment was made, "quads don't work on VHF"! This comment spurred an overnight design and assembly project that resulted in this 4 element optimum spaced quad beam. This same antenna design won the antenna gain measurement contest in the category of highest gain for the shortest boom length. It came in with a signal gain of 10.1 dBd. The next highest gain antenna was an Oliver Swan (later to become KLM) "bandpass" "log periodic" type yagi of 13 dB's with a boom better than twice as long.

The antenna should be assembled on electrically insulating material such as white polyvinylchloride "PVC" pipe. The first antenna of this type was fabricated of wooden furring strips, and 12 gauge copper wire. The dimensions are included in this information package along with recommended design tips. The antenna will provide a fine signal for any two meter home station, and has also worked well in the past for mobile or portable applications, as well as transmitter hunts!

Element dimensions

Using #12 American Wire Gauge (AWG.) THHN type copper wire like that used to wire electrical receptacles in home 115 Volt AC wiring, the wire lengths will be:

  • Reflector (Ref.) 86 inches (making a square loop that is 21.5 inches per side)
  • Driven Element (D.E.) 81.5 inches (or 20.375 inches per side) [Note feedpoint polarization]
  • 1st. Director (Dir. #1) 78 inches (19.5 inches per side)
  • 2nd. Director (Dir. #2) 75 inches (18.75 inches per side)

Leave the insulation on the wire! Strip off only a 1/2 inch at each end of the wire to either join and solder the loop elements for the Reflector and Directors, or to solder on the SO-239 or other female coaxial connector for the Driven element. The antenna will match 50 Ohm transmission line directly with no other device needed. An RF Choke of several turns of coaxial cable is recommended for symmetric antenna aiming.

After cross spreaders have been fabricated that are slightly longer than 1/4 th the element dimensions, they should be mounted on the antenna's boom. Let me emphasize again that all structural portions of the antenna must be fabricated from non-conductive materials. It is recommended to build the first such antenna you attempt from wood. Fabricating all pieces can be done with simple hand tools, and the element "spreaders" can be cross notched and secured to the boom with 1/4 X 3 inch bolts, nuts, and lock washers. The element spacings are as follows:

  • Reflector to Driven Element = 15.25 inches
  • Driven Element to Director #1 = 14.75 inches
  • Director #1 to Director #2 = 36.50 inches

Construction and Electrical Considerations

On the drawing with this article you will note the fabrication technique used for the wooden constructed antenna. A 1 1/2 inch TV antenna type "U-bolt" is used to mount the boom to the supporting vertical mast. 1 inch by 1 inch square stock was used for the boom, and 3/4 inch by 1 inch wooden strips were used for the element spreaders.

If the antenna is to be vertically polarized for use on FM (Frequency Modulation) or AM (Amplitude Modulation) the feedpoint connector should be installed as shown on the drawing. If Single Sideband (SSB) or Continuous Wave (CW) where horizontal signal polarization is used, the antenna should be rotated 90 degrees from that position shown. Thus for SSB or CW the spreaders would be vertical, and more to the point, the side of the Driven element where the coax connector is seen, would be parallel to the ground!

Finally by positioning the coax cable used, running it back to the boom along the driven element's spreader, an "RF Choke" type "Balun" can be wound around the boom using about 7 turns of coax. Belden RG-213/U or RG-58/AU are recommended. Hold this "choke balun" in place with electricians tape and or plastic "tie-wraps". If the smaller RG-58 is utilized, total coax length should not exceed 25 feet. Longer runs of this relatively "lossy" cable, will throw away signal gain wastefully on both receive and transmit! This smaller cable will also compromise the antenna's power handling capability. Using RG-213 the antenna can handle several hundred watts of power.

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