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
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
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 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
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
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 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 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 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 additional 5'-1"). These vertical
mast materials are very stout and are standard sizes,
available through most any supplier of aluminum. The 2"
tubing fits quite easily inside the Schedule 40 Pipe (with
.070" clearance), and a round shim for each of the
four 12" long overlapping joints was made by forming a piece
of 6.25"x14"x.020" aluminum to fit between the two
members. Each joint was then bolted using two
3/8" hardened steel bolts and washers, oriented orthogonal
to each other, and located 3" in from the end of each member
(5" between the bolts).
The masts are rigidly braced from the center to the midpoints with 1.5" aluminum tubing, and also guyed out to the antenna mounting locations with 1/8" steel guy wire (supported by a 4' long length of 2"x2"x.125" aluminum angle, and supported with 1"x1"x.0625 wall square aluminum tubing). One of the mast splicing bolts was used, in conjunction with a U-Bolt, to secure the mounting bracket for attaching the rigid bracing. The masts are also braced sideways (at the antenna mounting bracket points) with Phyllistran cable. The masts were mounted so that the center of gravity the mast (when both upper and lower antennas with feedline attached) was in the center between the two horizontal towers.
The horizontal framework is a "double H frame" using a total of eight 8' sections of Heights AC14-100 aluminum tower (for two 32' long towers), spaced approximately 2' on center from each other. I used a single 48' long piece of this in my 16 yagi 2m array, and it worked fine, but twisted slightly. The double H frame using that material, when properly guyed and supported, should be far superior, very lightweight, and more than adequate (this array only weighs half as much as my 2m array). The length of the pair of assembled aluminum tower sections is actually 31'-8". The centers of the masts were each mounted 4.75" in from each end, with the antennas mounted on the outside of the masts. This resulted in a horizontal stacking distance of 31',4-7/8" between antenna centers, which was very close to the targeted 31.5'.
4" aluminum channel is run diagonally above and below the two horizontal towers, onto which the 1-15/16" pillow block bearings from the elevation mount are bolted. With this configuration of the double H frame and diagonal mounting, the center of gravity and pivot point will be exactly in the center of the array. The entire properly balanced array is very easily elevated. The photo at the left shows one of the pillow blocks bolted onto the central elevation shaft (as viewed from below after the antenna was installed on the mount).
As is more apparent after the antenna is in the air (photo at lower right), the upper horizontal tower of the H frame assembly is mounted to the rear of the vertical aluminum support masts. The lower tower is mounted to the front of the vertical masts. There are a pair of 5' long vertical aluminum masts similarly mounted between the two towers (immediately adjacent to the central support channels) used to support the 3/8" heavy duty Phyllistran cables from the center of the array out to the ends of the horizontal members of the H frames (to prevent sagging of the H frame when the array is pointed at the horizon).
The array is also braced out the front, from a center point with cables running out to the end of each bracket where the tower is attached to the main vertical masts (to keep the frame from sagging when the array is elevated.
As shown in the bottom photo at the left, the weighted precision 3 turn elevation potentiometer that is used for elevation readout is mounted in a pair of metal film canisters. Nylon cable ties hold the assembly inside the lower tower section next to the mount.
|Side-to-side bracing is provided to prevent the yagis from
flopping over while elevated. This is done through the
use of 1/8" diameter Phyllistran cable, run just underneath
the elements on each yagi, from the boom to a fiberglass
cross member mounted near the center of each yagi. The
8' long pieces of fiberglass poles were cut from broken pole
vaulting crossbars (acquired through the courtesy from The
University of Montana track and field athletic
department). Plugs were put into the ends of the
fiberglass poles so the U bolts holding the angle aluminum
mounting brackets (for the Phyllistran cable turnbuckles)
would not crack the fiberglass. The plugs were
standard nylon fittings for bed casters (there is quite a
size selection of these at the local hardware store).
The fiberglass poles were lightly sanded, cleaned, and
painted with three coats of white paint formulated for use
on fiberglass (expensive, but also available from the local
ACE hardware store). The paint used was "Marine Topside
Polyurethane Enamel" by Valspar Corporation.
The antennas came with dacron ropes to support the booms from a temporary 24" high central support post that needs to be clamped to mast after the antennas are mounted. Galvanized 1/8" steel guy cable was substituted for the dacron line, and 25.75" long pieces of 1.25"x1.25"x.125" square aluminum tubing were bolted to the small guy support on each of the top two yagis. This extension of square aluminum tubing (weighing 1.35 pounds) makes a tight fit extending 4.25" down inside (past the top three mounting clamps - see photo) the tops of the round 2" masts (1.75" ID), and provides adequately stiff, permanent support for the boom guys.
The balance point for the yagi of course depends on the
particular feedline and support systems used. For my yagis,
the balance point was 20'-1/2" from the end of the N connector on
the DE feed block. By bending the feedline away from the
mast at a point 30" from the center of the yagi, approximately 19'
of LMR feedline weight is added to each yagi. The
completed, trussed up yagi (less feedline) weighed in at
approximately 49 pounds.
|The 50 ohm phasing lines were constructed
from LMR600 cable. The length of each line (with
connectors installed) was 42'-7.5", which corresponds to
2.5 wavelengths at 50.150 MHz (0.2
dB loss). This was confirmed by the short
shown by sweeping the open feedlines at 25.075 MHz
(where the length is 5 quarter wavelengths). The
weight of each completed phasing line with connectors was
approximately 5.83 pounds, approximately 2.6 pounds of
which was on each yagi..
With the extra electrical lengths inside the power divider and the two N chassis connectors, it was estimated that the actual overall length would be 2.5 wavelengths just under 50.100 MHz.
The 4 way 1/2 wavelength power divider was built from
1.25" OD square aluminum tubing with a .125" wall
thickness. The inner conductor was 15/32" OD round
hobby brass tubing, creating a line impedance of 50
ohms. Four .375" thick teflon spacers were evenly
spaced at approximately 20" intervals (between the
spacers or RF connections) through the inside of the
square tubing, to keep the center conductor supported
and centered. The overall length of the aluminum
tubing for the power divider was 10', with 57.75" (using
a velocity factor of .98) from the center connector to
the point where each pair of N connectors were
connected. (Next time I suggest using a velocity
factor of .975, since the low end of the 6m band was
just on the upper end of the bandwidth for a perfect
match with the device built as described
above). The estimated loss for half of
the power divider is less than 0.02
dB. The connector for the main feedline
was a 7/16 connector, to insure plenty of extra
durability in terms of handling RF power. The
flexible coax around the rotator was LMR600 ultraflex,
with 7/16 DIN connectors on both ends (0.1 dB).
|Initially, 3/4" diameter 75
ohm CATV hardline was used for the feedline, which
required an impedance transformation. This was
acheived by constructing an "L/12" impedance transformer
and mounting it at the top of the tower. The
transformer was designed around 1.25" OD (1" ID) square
aluminum tubing (the outer conductor, sized to accomodate
the connectors selected), with appropriately sized hobby
tubing to construct the required 50 and 75 ohm
sections. The 75 ohm section (toward the 50 ohm
antenna) was an 18.75" long piece of 5/16" diameter
tubing; the 50 ohm section (toward the 75 ohm feedline)
was an 18.75" long piece of 15/32" diameter tubing.
A single teflon spacer was used at the center where the
tubing sizes changed. At the antenna end (to
connect to the 50 ohm LMR 600 ultraflex), a 7/16 DIN
female chassis connector was mounted to the square
aluminum tubing of the transformer. On the feedline
end (to connect to the 3/4" CATV 75 ohm hardline), a male
HN connector was mounted to the transformer. The
feedline to the shack is 200' long.
In the shack, a traditional 1/4 wavelength long coaxial
impedance transformer (of 61.5 ohms) was used to convert
the 75 ohm CATV hardline back to 50 ohms. I constructed
mine from 1" "Type M" copper tubing (OD=1.125",
ID=1.055), with a 57.6" long piece of 3/8" OD hobby
tubing as the center conductor.
The 75 ohm CATV hardline was later replaced with 1-5/8 Heliax and the impedance transformers at both ends of the feedline run were bypassed. Total loss for the 200' of Heliax (with 7/16 DIN connectors on both ends), is 0.4 dB, resulting in less than 0.75 dB total line loss to the low noise preamp in the shack.
|The H Frame was first raised up and hung
against the tower so the bottoms of the vertical masts
just cleared the ground. Even so, the sign company
ladder truck could not reach up high enough to raise the
antennas up to the tops of the top of the masts (around
32'). Therefore a crane was used to raise the
antennas into place, and the bucket on the ladder truck
was used to stand in and reach up to tighten the
boom-to-mast clamps on the upper antennas.
The lower antennas of course were within easy reach of the ground, and were mounted by hand. The crane was then used to raise the complete array up to the top of the tower, where the H frame was bolted to the pillow block bearings on each end of the central support shaft of the elevation mount.
Power supplies to run power the elevation and prop-pitch motors, along with relays to enable actuation from the house, were enclosed in a waterproof plastic box mounted on the bottom of the tower. A messenger cable (low to permit clearance of the yagi reflectors when the array is pointed up at the moon) carries the feedline (3/4", 75 ohm CATV hardline), AC power cord, and 8 conductor control cable from the house.
The main tie-down ropes are 4 nylon lines attached to the center of the two vertical masts. "S" hooks were also mounted in the bottoms of the masts so 4 more secondary stabilization lines could be easily hooked on (by reaching up with a 15' long aluminum pole) when especially severe winds are anticipated. From experience with my 2m EME array, it was found that tie downs attached only to the central horizontal boom do resist winds trying to rotate the antenna in azimuth, but the "rocking" effect from forces acting on the elevation mechanism can completely destroy the coupling there. By also using tie-downs on the bottoms of the masts, such forces acting against the elevation mechanism can be limited.
The VSWR of the antenna is nearly perfect between 50.100 and 5.200 MHz, showing only a couple of watts reflected with 1500 watts forward. During the first weekend of testing, echoes off the moon were present over half the time, and moonset signals from the 9G5AN DXpedition were detected on almost every transmission they made. The charts at the top of the page indicate a beamwidth of about 10 degrees down to the 1 db point; although this may seem extraordinarily sharp to 6m operators used to being able to watch a very wide range of azimuths for incoming DX signals, it sure seems very comfortably broad for EME (at least compared to my 16 yagi array on 2m)! Before I had the indicators and remote controls set up, I was limited to visual aiming, and I confirmed that the antenna seemed to work fine as long as I went out to move it every 30 to 45 minutes! Even pointed through the trees at moonrise, echoes are quite good, and the antenna seems to perform noticably better than the single 70' long yagi at the 70' height, at least between 90 and 235 degrees azimuth. Aiming the antenna at northern cold sky produces a noise of 2.5 dB, compared to a 50 ohm load here in the shack.
More testing will be necessary to confirm, but the initial
comparisons show that the single yagi works better in directions
(such as Japan), where the lower yagis are essentially at ground
level within a dozen wavelengths, due to local topography.
In other directions in which the EME array has a clearer shot (
such as toward the Caribbean), the EME array is clearly a better
performer. A chart of the horizon
provides a more complete picture of some of the VHF challenges of
living in the northern Rocky Mountains! The antenna is
normally tied down at 110 degrees, which is aimed at Missouri
(1xEs), Georgia (2xEs) and eastern Caribbean (F2). It
has been very helpful to use the single big yagi at 70' to locate
DX stations, and then bring the GLEAP array around to the proper
azimuth when a few extra dB is necessary. Hope to contact
you with it soon!
During the first few years of operation, I have to say that I am very pleased with the performance of the array. The smallest station I have worked via EME was using 100w and a 3 element M2 yagi. Most of the single yagi stations I have worked were running more power and/or antnena than that. I did wind up having to replace the motor portion of the prop pitch motor in 2011. As of December, 2012, I have worked 128 DXCC via 6m EME and continue to add new DXCC at a rate of about 1 per month.
Most recently updated on 15 November, 2016