6 meter, 2 element yagi
A simple, compact and effective antenna for 50 Mhz.
This antenna was built in about an hour after using K6STI's AO simulation software to design it. The antenna was then taken to a hilltop near Rainier, Oregon (CN86) where it was deployed on a 12 foot mast for the 6 meter sprint contest. It worked very well, showing an excellent Front-to-Back ratio and good forward gain. After the contest the antenna was tested. It showed a 1:1.4 SWR match centered at 50.300 Mhz. This was improved to 50.150 Mhz by adding 1/2" to each element tip. Ground proximity and nearby objects will affect and may even improve the SWR and radiation pattern. These effects are much reduced at 20 feet or higher. Optimum E-skip height is about 30 feet above ground.
To build it you will need:
- 1/2" or 5/8" OD aluminum tubing - 2 pieces: 109" and 121" long
- 7/16" or 1/2" OD solid insulating rod - nylon, plastic, or wood - 6" long
- 1" ID plastic EMT electrical pipe or other plastic pipe - about 40" long
- #6-32 x 1" screws, washers, nuts. Stainless steel preferred.
- Boom-to-Mast mounting bracket. Home made or Radio Shack, etc.
Substitute 1/2" ID hard drawn copper water pipe if you can't find some 1/2" or similar size outside diameter (OD) aluminum tubing. Paint the copper with clear spray paint or other non-conducting color.
The insulating rod for the driven element should be strong, waterproof, and fit tight into the metal tubing. Cut the 109" tubing exactly in the middle and insert the insulating rod into both pieces until there is a 1/2" gap between the metal tube ends. Drill a 1/2" or 5/8" hole in the EMT pipe boom about 2" inches from the end and insert the driven element so the gap is inside the EMT pipe. Drill small holes through the driven element on both sides of the EMT boom and insert #6-32 screw hardware. Attach RG8, RG213, or similar low loss coaxial feedline to these screws as shown:
Mount the reflector element to the boom using a U-clamp. Element spacing is 35 inches. Install the boom-to-mast mounting bracket in the middle of the boom. Make the bracket out of a flat metal plate with U-clamps or just steal one from an old CB or TV antenna as I did.
The design antenna was optimized with AO for best match to 50 ohms, no matching network. A choke balun could be used to decouple any feedline currents. Wind up 8 turns of the feedline coax into a 6" diameter coil, then strap it close to the antenna feedpoint. Tape the coax turns tight together and tape or tie-wrap the coil to the boom.
Here's the original AO antenna design file:
2-Element 6 meter Yagi
Free Space Symmetric
50.150 MHz
2 aluminum wires, inches
refl = 61
drvl = 54
dirsp = 35
20 0 -refl 0 0 refl 0 .5
20 dirsp -drvl 0 dirsp drvl 0 .5
1 source
Wire 2, center
50 Mhz 2 element yagi built 5/13/2006
Used in the May Sprint contest.Here's the AO run file analysis:
Impedance 50.2 + j 1.5 ê
SWR 1.03
Wire Losses 0.01 dB
Efficiency 99.8%
Forward Gain 5.57 dBi
F/B 9.86 dB
Azimuth Beamwidth 71ø
Elevation Beamwidth 153ø
Gain or F/B ratio could be increased somewhat at the expense of a good match at 50 ohms. Optimum gain would be had with a shorter director element instead of the reflector. Optimum gain element spacing is 0.15 wavelength. Expect about 15 ohms. A gamma match will provide the easiest match.
Copyright 2006 - K7YO & Associates
