Hy-Gain 28 FM User manual

ORDER NO. 2085-1
MODEL 28 FM
8 Element, 2-Meter Beam PN 801318-
2
INSTRUCTION MANUAL
General Descri
p
tion SWR and Feedline
This antenna is an 8 element, optimum spaced,
2 meter beam. It features extremely high
forward gain, a clean radiation pattern and an
excellent front-to-back ratio. The dimensions
shown in Figure 2 produce a radiation pattern
with low sidelobes and backlobes over the
entire 2 meter band. This antenna comes with
stainless steel hardware for all electrical and
most mechanical connections, and now
features a new boom-tomast bracket that will
allow mast sizes of 15/8" to 2 1/16" in
diameter.
The 28 FM antenna has an input impedance of
200 ohms. The supplied balun matches the
input to 50 ohms. If you are using transmission
line with a characteristic impedance other than
50 ohms or 200 ohms, a matching device must
be made. Refer to any current Amateur
Handbook for information on constructing a
matching device.

Figure I
Overall View
Figure 2
Front and Rear Boom Detail
Tuning
NOTE: The Driven and Parasitic Elements are
adjusted independently in the following
manner.
Parasitic Elements: This antenna is pretuned
for maximum gain and best radiation pattern
at 144 MHz. This setting will give good
performance over the entire 144-148 MHz
band.
If you wish to optimize the antenna for a
frequency higher than 144 MHz, cut l/4" off
of the total element lengths for each MHz
higher than 144 MHz.
Driven Element: SWR can be lowered to less
than 1.2:1 at a desired frequency by
carefully trimming the driven element. Keep
the element symmetrical by cutting the same
amount from each side. Typical SWR curves
are shown in Figure 3A, and a cutting chart
is shown in Figure 313. Each installation is
slightly different, so cut the driven element
for the lower SWR at your particular
location. Measure the SWR as close to the
antenna as you can for accurate results.

Figure 3A
VSWR for Horizontal Polarization Onl
y
Figure 3B
Driven Element Cuttin
g
Chart
Stackin
g
The antenna can be easily stacked for ap-
proximately 3 dB more gain each time the
number of yagi is doubled. Refer to Figure 4
for stacking and phasing harness cutting
informa
tion.
The two phasing lines coming from the two an-
tennas to the "T' connector can be any odd
multiple of one-quarter wavelength in the 75
ohm transmission line. See Fi
g
ure 5.
NOTE: When phasing two antennas, the
Driven Element halves that are connected
directly to the phasing lines should be on the
same side of the arra
y
.
The feedline impedance is for 50 ohms (RG-
8/u). For detailed information on stacking
more than two yagis, please consult any
current Amateur Handbook.
Figure 4 Stacking Two
(
2
)
Antennas

Figure 5 Phase Line Cutting
Dimensions
Installation Ste
p
-b
y
-Ste
p
Assembl
y
This antenna fits a 1 5/8" to 2 1/16" outside
diameter mast. Remove the parts from the carton and check
them a
g
ainst the Parts List and the illustrations.
Mount the antenna in the clear. Surrounding ob-
jects-particularly power lines and other objects
of considerable mass or length -are detrimental
to the
p
erformance of the antenna.
WARNING
Do not allow any part of the antenna to
touch power lines. This could cause
severe burns or fatal injuries.
When mounting the 208S-1 with an HF beam
antenna on the same mast, the 208S-1 should be
on top. If the 208S-1 is to be vertically
polarized, separation of the two antennas should
be at least 2 feet. If the 208S-1 is to be
horizontally polarized, separation should be at
least 6 feet.
The mast, if metallic, should never be run com-
pletely through the plane of the elements.
Slightly reduced performance will be noticed if
a vertically polarized 2085-1 is mounted at the
top of a metallic mast as shown in Figure l.
Horizontally polarized mounting will not be
affected. For optimum performance with a
vertically polarized 208S-1, a wooden mast
should be used and the coax routed past the
reflector then dro
pp
ed to the mast.
Select the boom back-up plate, the boom-tomast
bracket and the four (4) 1/4"-20 x 3/4" bolts,
1/4" lockwashers and nuts.
Place the boom-to-mast bracket on the boom as
shown in Figure 6. The front and rear boom sec-
tions should meet in the middle of the boom-to-
mast bracket. Use the 1/4"-20 x 3/4" bolts in the
outside holes. Leave the inside holes for the two
(2) U-bolts, which will be used later for
mounting the mast. Select either the vertical or
horizontal mounting position. Adjust the boom
accordingly before tightening the bolts securely.
Select the R1 (40 1/4" rod). Use a pencil to
place a mark at the center of the rod (20 1/8"
from either end). Place two more marks 5/8"
from each side of the center mark.
Place a #10-24 x 1 1/2" eyebolt into the R1 slot
as shown in Figure 6, Detail A. Slide the R1
through the holes and the eyebolt until the outer
two marks on the R1 are visible on each side of
the boom. Slip on an aluminum half-washer, a
lockwasher and a # 10 nut. Tighten it just
enough to hold the rod securely. DO NOT
OVER TIGHTEN.
The antenna can be mounted either vertically or
horizontally for FM or SSB/CW operation
respectively. Circular polarization can be ob-
tained by using two yagis. For information
about which polarization to use consult local
Amateurs who use the fre
q
uencies
y
ou desire.
Select the element-to-boom insulator, two sec-
tions of the Driven Element (DE) 7/16" x 17
1/4" tubing) and a beta rod. See Figure 6, Detail
B.

Figure 6 Boom-to-Mast Clamp
Assembl
y
Figure 6-Detail A Parasitic
Element Attachment