N5GLR's "Garry" MOXON at 25 ft. on a push-up mast.
Note the "fly-by" in progress when this photograph was taken.

 

 

 

After reading N0KQH article on this web site, Garry decided to build his MOXON with a twist.  He elected to use 40 PVC pipe for the boom and supports in a standard yagi configuration and RG58 coax for the elements and feed line for a 20 meter beam.  

Garry configured the coaxial elements much like a Bazooka antenna. That is, each leg of the driven element is fed using the center conductor and the center conductor and shield are terminated at the ends.  The feed line is connected normally (ie. shield to one leg and center conductor to the other).  It has resulted in an antenna who's driven and reflector element length are shorter than a conventional wire MOXON yet performs equally well.

Garry is still experimenting with boom length.  Here are the current specifications for his MOXON:

Driven element - 20 feet overall (10 ft. each leg) (element support
is 14 ft overall)

Relector - 21 feet (element support is 14 ft. overall)
Boom - 9 ft.

Height above ground - 25 ft.

Weight - approx. 7 lbs.

Impedence - 52 ohms (as measured with 259B analyzer)

SWR @ 14.040 - 1.3 : 1

SWR @ 14.350 - 1.5 : 1

Garry reports that the performance of his MOXON, when compared to his inverted Vee (no. 14 ga. insulated wire) at 25 ft., is not quite what he would like.  In most directions, the Vee is approx. 1/2 to 1 S unit better than the MOXON but, in some directions (probably the nulls of his vee), he is seeing as much as 2 to 3 S units gain.  Gary emphasizes that the signal to noise ratio of his MOXON is supererior to his VEE.  An S4 - S5 noise level on the Vee will almost completely disappear on the MOXON.  The signal strength will change a little depending on the MOXON's heading (as noted above) but, the noise level drops dramatically.  Garry attributes this to the fact that the MOXON is fully horizontally polarized and the "Bazooka" style of construction.  It's also very broad banded and front to back ratio is approximately 3 S units (as observed).  It's also quite inexpensive to build at under $20.

Garry realizes that his antenna is a Hybrid Moxon  as the ends of the reflector and director are not close enough to "couple" (as described by Carl Cebik).  He shortened the boom once from 9' 6" to 9' and noticed an improvement and plans to shorten it more, in small increments, in an effort to improve gain. 


Garry finds himself using his Hybrid MOXON more and more due to the low noise characteristics  even though he feels that he is often loosing as much as an S unit in signal strength in some directions.  He says that if he can get it to perform equally with the Vee he will be a pleased and if he can get some additional gain over the Vee, he will be all the more delighted!
 

 

Email Garry at rowdyjoe@comcast.net for additional information about his Hybrid 20 meter MOXON.