6 Meter Moxon Wire Antenna

Interested in giving 6 meters a try?  The six meter band is open to all FCC licensed amateur radio service operators except Novice class.  Take a look at a Moxon 2-element manually rotatable wire beam antenna.  The antenna is relatively inexpensive, easy to build, and performs well at a height of 20 feet.  A free MOXGEN app (courtesy of AC6LA) is available to compute the wire lengths and gaps for a specified frequency.

MOXGEN computations

 I decided to build my antenna using #14 AWG black THNN stranded wire and a treated wood frame.  The center section is made from a piece of 2 X 6 with a short piece of 1 1/2” diameter galvanized pipe threaded into a floor flange bolted to the  2 X 6.  The threads on the unattached end of the 1 1/2” diameter piece of pipe were cut off and a 5/16” hole drilled through the pipe.  A 1/4” galvanized bolt secures the wood frame to a 20’ long galvanized metal pipe mast.  If you decide to use galvanized pipe sections to fabricate a mast, consider using a pipe sleeve at the joints instead of threaded couplers. Pipe sections joined with threaded couplers tend to break along the threads at the couplings when flexed during mast raising and lowering operations.  I cut the threaded ends off two 10’ sections of 1” diameter galvanized pipe, butted the ends together, and bolted a sleeve made of 1 1/2” galvanized pipe over either sides of the joint to provide the needed support.  The wood frame and metal mast were spray painted camouflage forest green to reduce the visibility of the antenna.  A 1:1 current balun is attached to the frame at the antenna feed point with a hose clamp.  If you use a balun, check to be sure it is rated for operation on the 6 meter band (50 – 54 MHz).  Fifty feet of RG-8X coax serves as the transmission line.  If possible, use a low loss coax such as Belden 9913-7F to keep transmission line losses as low as possible.  A 200 pound concrete pedestal secures the base of the antenna and facilitates raising and lowering operations.  The mast slides into a 4’ long section of 1 1/4” galvanized pipe embedded in the concrete.  The 1 1/4” base pipe section was drilled and tapped to accept a 1/4 X 20 TPI galvanized thumb screw to lock the mast in position. The antenna has good gain along the main lobe, an attractive “take-off” angle, and is easy to rotate by hand.

Tip #1:  For manually rotatable antennas, it is helpful to provide a fixed reference pointing to North (magnetic or true) and a moving pointer that indicates bearing relative to North.  I used (2) pipe hanger clamps and 4″ long 1/4″ X 20 galvanized carriage bolts to provide an orientation mechanism for my antenna.  A 1 1/4″ hanger clamp + carriage bolt was attached to the fixed 1 1/4″ diameter base pipe section.  A compass was was used to find magnetic North. The magnetic declination for my latitude/longitude was estimated using the free NOAA Magnetic Field Calculator.  The magnetic declination for my area was added to the magnetic North bearing to determine true North.  The antenna  was oriented so the center of the major lobe points to true North.  A 1″ hanger clamp was attached to the rotatable part of the mast and aligned with the lower reference marker.  When the antenna is rotated, the movable marker indicates bearing from true  North.

Tip #2:  If you have an account with qrz.com and are logged in, you can obtain the bearing and distance to a registered QTH by performing a call sign lookup.  The distance and bearing (relative to true North) can be displayed by clicking the detail tab.  Use the bearing to orient your antenna.

Antenna orientation mechanism

 Bottom view of antenna showing wood frame connection to mast

image

Re-enforcing pipe sleeve over joint

moxon-02

Top view of antenna

image

Erected antenna

image

Predicted radiation pattern (EZNEC+ 5.054)

image

Predicted SWR curve (EZNEC+ 5.054)

image Actual SWR curve (AIM-4170C; software release 858)

image

A number of factors can affect the SWR curve of the completed antenna including proximity to trees, structures, other antennas, soil conditions, balun quality, length and type of the transmission line, etc.  My antenna is easily tuned using a Palstar AT-500 manual tuner.  Most automatic antenna tuners will tune the antenna with no problem.

The EZNEC+ model for the antenna can be downloaded from the link below.

6 meter Moxon EZNEC model

 

 

 

0 Responses to “6 Meter Moxon Wire Antenna”


  • No Comments

Leave a Reply