Geomagnetic Latitude Equalizer Antenna Project
W7GJ 6m "   GLEAP "   EME Array
Design, Construction and Performance Notes

BACKGROUND

Yes, I undertook the HUGE process of building an array of four of the 50' long M-Squared 6M9KHW yagis - I highly recommend this array as a "realistically manageable" size, yet with enough gain to really get the job done effectively.  At the time of its raising (October 27, 2001), it was the third largest fully steerable ham radio antenna array for this frequency band in the world.  Why is it so important to have a fully steerable antenna, you might ask?

There are very few 6m DX stations with EME tracking capability, so it is ESSENTIAL to have elevation capability up to 65 degrees.  With my single yagi, I can only elevate to 45 degrees, which is really unfortunate because I was missing EU moonset under the best times of month (which in 2001 were coinciding with most northerly declination, putting the moon WAY HIGH here!).  The new GLEAP array is capable of elevation to 90 degrees.  Although this extra margin of elevation not necessary at this latitude for moontracking, it may be useful for driven element maintenance access, if required, sometime in the future.

 It is very desirable to have at least 1500W on 6m EME if you want to have any success.  Conditions on 6m can be VERY erratic - it is a terrible band for EME....however, it is the ONLY way to work any 6m DX from up here in the "geomagnetic far north".  I think if you put up an array such as four of the 6M9KHW yagis, you will have a killer system for working other kinds of propagation, too (if you happen to live in a place that HAS any other kind of propagation- HI).  And, it should be possible to more easily work DX stations on their moonset with a kw and a single good yagi.

Most of the folks who have tried 6m EME and given up due to lack of success and/or activity have had very little antenna gain, so have been severely limited by the number of  larger stations they could work.  Note that even a four bay array of 5 or 6 element yagis only has the same amount of gain as my single 6M35WL/6M11JKV yagi, which I consider to be the minimum antenna size for 6m EME.  With my single yagi, I DO hear my own echoes  when I am pointed skyward (no ground gain) and the conditions are optimum (quiet background sky, moon near perigee, no auroral disturbances, etc.) but performance is quite erratic.  Just as on 2m EME, though, there is a "magic minimum point" in antenna gain where you can begin to have some reasonable success....and increasing the gain above that point dramatically increases the number of stations you will be able to contact.  The 4.5 dB additional gain from this four yagi array should greatly improve the reliability for EME QSO's with other smaller stations.

MINIMUM ARRAY SIZE

Having said all that about my array, I have to add now that very successful 6m EME results can now be obtained by using JT44 and a smaller array.  I truly believe that a very practical sized array for success using JT44 is an array of four 6M5X yagis.  This sized array is very simple to build and elevate, and has approximately the same gain as my single yagi, with which I hear my own echoes while pointing upward.  As long as it has 14 or 15 dBd gain, such a steerable array should have no trouble making contacts with larger 6m stations on CW, or with many stations on their horizon using JT44.  I suggest constructing such an array using a "double H frame" of aluminum tubing.  It could be very conveniently mounted on a 25' high tower.

MY ARRAY DESIGN

The array was designed to be able to provide a stacking distance of 31'' wide x 29.5' high, with the center of the array at 32' above ground level.  Here is the expected performance of the array:

Azimuthal pattern (courtesy of K0GU):
 
 


 

Elevation pattern (courtesy of K0GU):

While pointed at the horizon, the new array appears to have more gain than the maximum ground gain lobe of the single 6M35WL/6M11JKV at 70', over the entire range of 2.5 to 9.5 degrees elevation.  Therefore, I expect it to be a very good performer when the moon is on the horizon, as well as for use on ground wave and during ionospheric openings.
 

SPACE PLANNING AND PREPARATION
Over 2 dozen trees were cut down and stacked in the spring of 2001 to make room for the new array.  Before any excavation could be done, all the slash (the limbs) needed to be burned.  Here we are rushing to burn the slash in the spring before it becomes too dry, and they no longer permit such burning. (You can see the 2m EME array is in the background).

Clearance for the array was calculated using my old DOS program "SPACE" (available for free download from the software section of my web site).  Below  is a printout from that program, showing  what the clearance looks like for this array.

CLEARANCE CALCULATIONS FOR ARRAY OF FOUR 6M9KHW 6M YAGIS AT W7GJ

     HORIZONTAL SPACING BETWEEN                   TOWER HEIGHT= 32
     OUTERMOST YAGIS= 31
                                                  VERTICAL MAST HEIGHT FROM
     LENGTH OF REAR HALF                          PIVOT TO LOWEST YAGI= 14.75
     OF EACH YAGI= 22.5
                                                  VERTICAL MAST HEIGHT FROM
     LENGTH OF FRONT HALF                         PIVOT TO HIGHEST YAGI= 14.75
     OF EACH YAGI= 27
                                                  LAST DIRECTOR LENGTH= 8.7
     POLARIZATION= 0 DEGREES
                                                  REFLECTOR LENGTH= 9.75

                   MINIMUM       FRONT         FRONT       REAR        REAR
    ELEVATION      GROUND        CLEARANCE     TURNING   CLEARANCE     TURNING
    IN DEGREES     CLEARANCE     HEIGHT        RADIUS    HEIGHT        RADIUS
    ==========     =========     =========     =======   =========     =======
         0           17.25         17.25        33.51      46.75        30.35
         5           15.35         19.66        34.47      44.73        31.25
        10           13.57         22.16        35.27      42.62        32.03
        15           11.93         24.74        35.89      40.42        32.68
        20           10.44         27.37        36.32      38.17        33.18
        25            9.12         30.04        36.56      35.86        33.53
        30            7.98         32.73        36.61      33.52        33.71
        35            7.01         35.40        36.46      31.18        33.74
        40            6.24         38.06        36.11      28.84        33.60
        45            5.66         40.66        35.57      26.52        33.30
        50            5.28         43.20        34.86      24.25        32.85
        55            5.11         45.66        33.97      22.03        32.24
        60            5.14         48.01        32.93      19.89        31.50
        65            5.37         50.24        31.75      17.84        30.63
        70            5.81         52.33        30.45      15.90        29.66
        75            6.45         54.26        29.07      14.08        28.60
        80            7.28         56.03        27.63      12.40        27.48
        85            8.30         57.61        26.17      10.87        26.32
        90            9.50         59.00        24.73       9.50        25.15
 
THE TOWER
The center of the antenna is 32' high, which will allow me to reach the DE on each yagi with a tall stepladder if I need to for some reason.  This low antenna height means I will not need guys.  I am using 35' of Rohn 55G tower (with the bottom 5' anchored in concrete), with "tripod guys" of 1-7/8" OD diameter steel pipe (three pieces of 1.5" IPS Schedule 40 pipe x 21' long) solidly supporting the tower at the 17-1/2' height, and anchored in concrete 5.5' from each tower leg ( in 18" diameter holes, 3' deep).  Back fill from all the holes was piled up over the locations of the tripod guy pipe anchors, in order to increase the frost protection for the concrete bases.

The bottom of each brace has rebar through it to attach it to the concrete, and the top end is fastened with a single large bolt, through the brace placed into the center of an 8" length of steel channel (which is bolted to each tower leg).  This is the same support system I have used for decades on my 16 yagi 2m EME array.

The lower 25' of  tower was assembled and single-handedly positioned in the hole with the assistance of a "skyhook", which was a pulley hanging on a 1" diameter nylon rope between two trees.  A come-along winch was used to pull the line going up through the pulley and down to the tower.  The tower was held plumb during pouring of the concrete through the use of come-along winches attached to polypropylene ropes attached to the top of the second section.  The top section can be seen sitting on a cable spool in the left of the photo below.

The top section of tower was also added by me alone, using the "skyhook" lines.  This photo to the left shows me atop the complete tower, along with the hoisting ropes hanging overhead.

MAST AND MOUNT

The mast is 1.5" IPS schedule 40 steel, with 1.5" steel tubing (.120" wall) welded inside it.  Atop the mast is a 31" long piece of 1-15/16" steel shaft welded to atop a 26" long piece of 6" wide steel channel,  braced by pieces of 3" wide steel channel, which extend down to the mast at a 45 degree angle.  2"x2" steel angle is welded on both sides of the shaft ends and top.  An 8"x8"x1/8" steel mounting plate is welded at the intersection of the braces and masts.  This mounting plate, along with a large piece of 6" wide aluminum channel, provide the attachment for the reversible DC gearmotor (which requires 200 VDC), right angle reduction gearbox, and idler sprockets  for the elevation drive chain. 

These photos show the mount on the top of the tower, with the weather cover removed over the gearmotor, gearbox, drive/idler sprockets.  The photo at the left shows the elevation chain and antenna installed.

THE ROTATOR














The rotator is a "medium sized" prop pitch motor.  This size motor just barely fits inside the tower, but cannot be installed through the assembled tower, and had to be mounted before the top section of tower was lowered over it and bolted in place.  In usual fashion, the prop pitch motor itself is bolted to the underside of the motor mounting plate.  A circular 1" high strap was welded to the rotor mounting plate to act as a barrier to prevent water from running down into the top of the motor.  You must protect the prop pitch from weather coming down inside the center of the motor.

The unit used had a pipe fitting welded inside the drive sprocket, so a mast coupler was fabricated to attach to this fitting.  Inside the center of the bevel gear, a pipe adapter (of almost the same diameter as the inside of the bevel gear) had been welded, as you can see in the top photo to the right.  What I decided would be easiest to do, would be to attach my mount to that pipe adapter.

As you can see in photos, I sawed with a hack saw, and filed to create two flat faces on the pipe flange so that I could place some 2" angle iron (painted brown) against those flats on each side.  I then secured these two pieces of angle iron on opposite flattened sides of the the pipe flange with (3) 3/8" diameter hardened bolts.   The two outer bolts go around the pipe flange.  The center bolt sits in a slot that I filed into the  two edges of the pipe flange; this center bolt resting in the slots, and the two opposite angle iron pieces tightened against the flattened faces of the pipe adapter, makes the flange assembly very well seated so it will NOT slip.

Then, onto the top of this platform formed by the two brown angle iron pieces, I bolted the yellow mast clamp assembly, which is shown in photo to the left.  It was mounted onto the brown angle flanges so that the mast would be centered directly over the center of the prop pitch axis.  The yellow mast clamp was  made in two halves.  Each half has a piece of angle iron welded to a piece of iron plate.   Hose clamps were then used to tighten the clamp halves around the mast, and the clmap was then bolted down to the brown flanges.

A conical weather shield was then fabricated from sheet metal and installed to cover the clamp and mounting plate.  As with the top tower section, the XYL (the official painter on the project) added the camoflauge paint job ;-)  I then sealed the top of it with rubber and plastic flanges from the hardware store, which permit the mast to rotate without binding on the weather shield.

Although the mount as connected to the prop pitch cannot slip at all, the mast can slip inside the clamp.  Since the array is tied down when not in use, this feature assures that nothing in the mechanical coupling between the motor and the antenna will break.  The azimuth indication is obtained by coupling the rotation of the mast to the rotation of a potentiometer, using a timing belts, so only the actual position of the antenna is displayed.  If a less forgiving connection is desired, bolts could be installed through both the yellow clamps and the mast.

In 2011, the motor in the prop pitch stopped working, and I replaced it with a separate new DC reversible motor.  Details of this repair are shown HERE.








The prop pitch motor is slow to start, but revs up as the antenna begins to turn.  To minimize the mechanical shock on the mast-to-motor connection assembly, a transformer was selected to provide very low unfiltered voltage - around 22 VDC.  In addition, resistors were added in the primary of the power supply, to slow the start-up of the rotation.  The antenna now rotates at about 1 degree per second, which still provides some stress on the mast connector assembly when the antenna stops.
 
THE H FRAME



 


 

I am using 30'-2" long aluminum vertical masts for the yagis (constructed by using a center 20' long piece of 2" IPS schedule 40 6061-T6 PIPE, with 2" 6061-T6 TUBING, .125" wall, telescoped 11" inside it to lengthen each mast end an addi