W8EGB's 40M Reversible Moxon
I was encouraged recently on 40m to submit the information on my 40m Reversible Moxon rectangle.
The dimension are as follows:
Each side is 51 feet long and the "turned in" sections are each 7.7ft long. (Each side is obviously the same length) The boom is 16.5 ft long which puts the element ends 1.1 ft apart. I bring down equal lengths of 50 ohm HALF WAVE LINES ( watch the V.F.) from each element cut for about 7.100. The elements are #14 covered wire.
By means of two double pole relays, necessary to completely isolate each element, I can reverse it NE or SW. I have seen F/B ratios as high as 40db in the CW end of the band and up to 30db in the phone band. I have two different settings for the reflector stub, one for ssb and the other for cw. The phone stub is almost a dead short across the relay and the cw stub is 16.5 inches. The stub is made up of #8 wire (because I had it) and spaced 2" apart. There are NO BALUNS in this system anywhere. I think they are superfluous.
This antenna replaced a full size 2 el yagi spaced 21ft and fed direct with 50 ohm line also. In the last CQ WW and ARRL DX Tests this antenna performed every bit as well as the former yagi. It is a no brainer because now I have two directions, both ends of the band, and umpteen more DB of F/B ratio. Eznec shows abt .2db less forward gain than the Yagi. It has been up since fall 2005. It is perfectly horizontal with 4 ropes spread to 4 trees. (It is actually mounted on a 136ft rope boom which supports my 5 element monoband 30m yagi in the middle and out in front the 3el 20m monobander. I have 5 wire yagi's fixed on EU total plus 2 LAZY-H's and a 80mtr flat top all fed with open wire lines to fill in the holes the fixed beams don't cover. NO towers, all tree supported. You want to know how high it is, 45ft, but that is very misleading because it looks across my lake into EU and the lake is 35ft below the front of all the antennas. EZNEC shows the equivalent radiation height of 80ft.
In the reverse direction it is even better as there is another lake to the SW and it is 45ft below the ant height. To be fair I should say that pointed toward EU I have a bit more gain that a single modeled Moxon because the 30M beam in front has current flowing on it and instead of about 4.5dbd I see nearly 5.5dbd in the NE direction. There is no difference to the SW as there is nothing behind the Moxon in that direction.
This antenna was done in QST by W4RNL. (check his web site for more information)It has high F/B and good bandwidth SWR. This particular design can be switched for reverse directions as the elements are all the same length. I bring down equal lengths of half - wave (about 7.2 mhz so I can use it at both ends of the band) lines and by means of two relays put a stub across the one I want to be the reflector and feed the other. Of course it is necessary to switch both center and shield lines so there is no coupling between the two elements. I used a full size 2 element for 9 yrs and it worked great but the F/B was nothing like this antenna and the gain was the same.
I can be found most nights on 40M ssb around 7185 - 7198 at 4-5:30 pm.
Steve Hammer, K6SGH