M2 Antenna Systems 20M5-125 User Manual

M2 Antenna Systems, Inc.

Model No: 20M5-125

SPECIFICATIONS:

Model ......................................... 20M5-125

*FR / (G) FS / (G) OG . ............... 14.0-14.350 / 10.2dBi / 15.8dBi @70’

*FR / (G) FS / (G) OG ................. 14.1-14.350 / 10.3dBi / 15.9dBi @70’

*FR / (G) FS / (G) OG ................. 14.1-14.225 / 10.6dBi / 16.0dBi @70’

*FR / (G) FS / (G) OG ................. 14.0-14.300 / 10.2dBi / 15.8dBi @70’

Front to back ............................... 24 dB Typical

Beamwidth ................................ E=50° / H=64°

Feed type .................................... Hair pin match

Feed Impedance. ........................ 50 Ohms Unbalanced

Maximum VSWR ........................ 1:2.1

*Subtract 2.14 from dBi for dBd / FR = Frequency Range / G = Gain / FS = Free Space / OG = Over Ground

Input Connector ....................................... SO-239, Others avl.

Power Handling ....................................... 3 kW, Higher avl.

Boom Length / Dia .................................. 44’ / 3” x .125 Wall

Element Length / Dia. .............................. 36.5’ / 1-1/2” To 1/2”

Turning Radius: ....................................... 32’

Stacking Distance ................................... 48’ To 62’

Mast Size................................................. 2” to 3” Nom.

Wind area / Survival ................................ 12 Sq. Ft. / 125 MPH

Weight / Ship Wt. .................................... 135 Lbs. / 161 Lbs.

FEATURES:

The 20M5-125 is the perfect balance between wind area and performance. It features improved gain and F/B across
the 20 meter band. The 20M5-125 mph is computer optimized mechanically for maximum strength for it’s wind area.
Mother nature will hate this one! Two different optimization options allow the antenna to be customized for your
bandwidth and performance preferences, Plots with gain and F/B figures are supplied. Physically, the 20M5-125 Yagi
features tapered elements, each element is secured with a pair of machined, 1/2” thick aluminum boom-to-element clamp
plates. The clamps also permit spacing adjustments on the 3” x .125” wall boom. Elements taper in size from 1-1/2” to the
adjustable 1/2” tips and are single and double sleeved at critical points to achieve a 125 MPH wind survival rating. All

M2 Antenna Systems, Inc. 4402 N. Selland Ave. Fresno, CA 93722

Tel: [phone] Fax: [phone] Web: www.m2inc.com

©2016 M2 Antenna Systems Incorporated

01/20/16

Rev.02

20M5-125 ASSEMBLY MANUAL

M2's 20M5-125: The inside story

(Customizing for maximum advantage)

The design concept behind the 20M5 and the 20M5125 is to allow you to CUSTOMIZE the antenna
to your needs and location. The latest computer techniques have been employed to produce the
attached set of patterns and associated element spacing and lengths. The program used allows
optimization of the Yagi not only for specific bandwidths, gain and F/B, but also for any height
above ground and stacked pairs.

Look over the optimization choices carefully and make a note of the one that best suits your needs.
The assembly manual that follows has element tip and spacing settings for your choice. We are
sure that you will end up with an exceptional antenna and you will also learn more about Yagis in
the process.

The computer program used to generate the plots and optimize the Yagi is YO (Yagi Optimizer)
created by Brian Beezley, K6STI. The figures generated by the program have been checked
against NEC and generally are within a few hundredths of a dB.

You may be accustomed to seeing inflated numbers on spec sheets and in advertising. Don't
worry, the inflated numbers may be referenced to Isotropic (dBi), which is 2.14 dB higher than a
dipole reference (dBd), or including as much as 6 dB of 'GROUND GAIN'. Other possibilities
include errors or ''marketing" guys that simply decided that a higher number would sell more
antennas.

Actual realized gain, in the case of plots over perfect ground, may be somewhat less than the
figures indicates. Most of us don't have perfect ground. Not only does the quality of the ground
itself affect the actual number but, in most cases, the things above the ground. Houses, buildings
and heavy trees all eat up the part of your pattern needed to generate ground gain.

To put this in perspective take the case of a station using a 5 dBd tribander up 70 feet located in
open farmland of normal ground. The net gain at 13 degrees radiation angle is probably 10 dB.
Compare that station to the 8.6 dBd monobander at 70 feet in the middle of a housing tract with
perhaps only 2 dB of additional ground gain for a net of 10.6 dB. In a pile-up it would be a flip of a
coin who would get through first. However, reverse the situation and the monobander would be
ahead by miles.

Understanding this fact of life may not ease your frustration, but at least you can understand why
some small stations do quite well and why some big stations are almost unbeatable. The flexibility
of the 20M5 design at least allows you the get the most you can out of your QTH.

STACKING ANTENNAS for more gain can be most beneficial, however, some designs don't stack
very well. Pattern and gain don't come up to expectations. The YO program allows us to optimize
the gain and pattern for a stacked pair of 20M5125s. With the availability of rotating rings and
rotating tower sections, more and more Amateurs will be taking advantage of the benefits of
stacking. Think about it. The increased vertical capture area reduces fading and the compressed H
plane pattern increases the efficiency of the signal as it reflects off the ground and ionosphere be­cause the energy is reflecting off these mediums at a more grazing angle. While many computer
programs don’t indicate a reduced angle of radiation for stacked Yagis, our results over the years
indicate a greatly reduced radiation angle for stacked arrays.

20M5-125 ASSEMBLY MANUAL

NOTE: THE “DIMENSION SHEET” AND THE “HARDWARE ARRANGEMENT” DRAWINGS ARE
QUITE COMPLETE WITH ASSEMBLY INFORMATION. EXPERIENCED BUILDERS MAY NOT
REQUIRE THE WRITTEN INSTRUCTIONS. WHEN IN DOUBT, USE THE WRITTEN WORD. ANTI­SEIZE PASTE (PENETROX OR NOALOX) IS RECOMMENDED ON ALL HARDWARE THREADS
AND ALUMINUM JOINTS. TOOLS REQUIRED: Electric drill, screw driver, 11/32" spintite or socket,
7/16" end wrench, 7/16", 1/2", and 9/16" socket set, measuring tape.

1. Determine which CUSTOMIZATION OPTION you prefer by looking over the Specification page and
Plot printouts. USE THIS CHOICE TO SELECT THE CORRECT TIP LENGTHS, ELEMENT
SPACING, AND MATCH SETTING AS YOU COMPLETE THE ANTENNA ASSEMBLY. For ease of
assembly and for future reference, space has been provided on the Dimension Sheet to record all the
critical measurements for the optimization option you select.

2. Pair up 1/2” element tip sections by length. Insert 1/2” sections into the swaged end of the 3/4” x
53” sections secure with 5/8” Compression Clamps (SEE COMPRESSION CLAMP & TIP ASSEMBLY
DETAIL). Set the proper exposed tip length according to the table below. DIMENSIONS GIVEN ARE
FOR 1/2” LENGTHS EXPOSED BEYOND THE 3/4” ENDS.

CW-LO FONE FULL BAND
REFL 51.625” 51.625”
D.E. 37.00” 35.25”
D1 36.00” 34.25”
D2 31.50” 30.75”
D3 25.875” 24.00”

Install all tip sections. Use a felt pen and masking tape to identify each element set by position as it is
completed.

3. Slide a 7/8” X 23” EXTERNAL SLEEVE over the butt end of a 3/4" x 53” / 1/2” tip assembly and
align holes. Install this assembly into the end of a 1" x 48” element section with holes at 1/2” and 1­1/2” from end. Use 8-32 x 1-1/4" screws and locknuts at the joint. Tighten securely. Slide a 7/8” x 32”
SLEEVE SECTION into the butt end of the 1” section and align holes. Attach a 1-1/4” x 48” ELEMENT
SECTION to 1” ELEMENT SECTION using 8-32 x 1-1/2” screws and locknuts. Repeat for all
elements.

4. PARASITIC ELEMENT ASSEMBLY: Slide a 1-1/2” x 30” INNER ELEMENT SECTION onto each
end of a 1-3/8” x 52” CENTER SLEEVE, align holes, and secure with a 1/4-20 x 2” bolt and locknut.
Slide on the second 1-1/2 x 30” section. Align the holes and secure with the second 1/4-20 x 2” bolt
and locknut. Place a clamp plate one either side at the center of this element assembly and rotate so
the bolt heads are up. Add the 1/4-20 x 2-3/4” bolts trough the 6 holes and add the locknuts. Check
the element centering again and then tighten the clamp block bolts evenly to keep the plates parallel.
Repeat for the other two PARASITIC ELEMENTS.

5. DRIVEN ELEMENT ASSEMBLY: Refer to the HARDWARE ARRANGEMENT drawing and
assemble THE LAST pair of ELEMENT CLAMP PLATES including the “L” BRACKET for mounting the
balun. Slide in the 1-1/4” x 24” fiberglass rod, center it, align holes up and down and tighten the clamp
bolts evenly. Now add the white poly rings to each side of the fiberglass rod and push them up against
the clamp plates. Insert the 1-/38” x 26” sleeves into the last two 1-1/2 x 30” SOE tubes. Align the
holes and carefully slide these assemblies over the fiberglass rod ends. Align all the holes and, FROM
THE BOTTOM, insert two 1/4-20 x 2-1/2” bolts. Drop on two HAIRPIN CLAMP BLOCKS and add a
locknut finger tight to each bolt.

20M5-125 ASSEMBLY MANUAL

6. BOOM ASSEMBLY: Inspect the CENTER BOOM SPLICE for any nicks or scratches. File smooth if
any found. Locate Boom Section (3” X 0.125” X 180”) swaged (1) end & Boom Section (3” X 0.125 X
180”) straight. Before joining boom pieces together, lightly oil or lubricate the COUPLING RINGS &
insert Boom Stiffener assembly into straight boom section. Insert Boom Stiffener assembly
approximately 17” from the end. Make note: This is end must be positioned to the rear of the
completed boom. This will center boom stiffener over the boom to mast plate (see dimension sheet).
Add final Boom Section (3” X 0.125” X 180”) swaged (1) end to complete boom. Secure all boom
sections using 1/4-20 x 3-1/2 bolts and locknuts.

7. Orient the eyebolt eyes to the top of the boom. Place the boom on bucks or equivalent to get it to a
convenient working height. Position one PARASITIC CENTER SECTION one inch from the end of the
boom, add the saddle clamps and the four 1/4-20 x 3” bolts (a dab of Noalox on the threads make
insertion easy). Align the top of the clamp to the eyebolt and tighten the saddle clamps evenly. Next,
refer to the DIMENSION SHEET and using a tape measure and a marking pen or piece of tape, mark
the ELEMENT LOCATIONS on the boom. Your choices are:

CW-LO FONE FULL BAND
REFL 0” 0”
D.E. 54.50” 61.000”
D1 116.00” 127.00
D2 323.00” 325.00”
D3 528.00” 528.00”

Dimensions represent the edge of the rear clamp block for each element. Now mount the center
element assemblies on the boom the same as the reflector. Align each with the reflector and tighten.

8. HAIRPIN MATCH ASSEMBLY: Refer to the HARDWARE ARRANGEMENT drawing. Insert a 1/4-20
X 2-1/4” bolt from inside the band clamp and Install the band clamp loosely positioned about 30” inches
in front of the driven element. Mount the BALUN using the 2-1/2” U-bolt and cradle but do not over
tighten. Remove the finger tight nuts over the hairpin clamp blocks and place the balun lead lugs over
the studs and replace the nuts finger tight. Next, slide the short bent end of the 3/8” tubes into the
small hairpin clamp blocks and flush the ends of the tubes with the blocks. Align and tighten the clamp
block bolts lightly. Install the shorting bar on the straight ends of the tubes and add the 1/4-20 x 1/4” set
screws, but do not tighten on to the tubes yet. Set to the proper shorting bar dimension, align and
tighten the set screws securely. Move the band clamp under the shorting bar, add the 3/8” spacer tube
on the stud and drop the shorting bar over the stud and add the locknut. Tighten the band clamp, and
then tighten the nut.. The dimension for your selected band coverage is:

CW LO FONE FULL BAND

28.00” 31.500”

Refer to the DIMENSION SHEET. This dimension is from the inner edge of the shorting bar to the inner
edge of the tube. Install the main feedline or feed line jumper on the 1:1 balun. Tape the connector up
carefully. Use the large cable ties to secure the cable to the boom.

9. INSTALLING THE ELEMENT TIP SECTIONS: Start with the REFLECTOR tip sections and insert
each double wall 1” element butt into the 1-1/4” center sections. align the holes and insert the 8-32 x 1­1/2” screws. Add the locknuts and tighten securely. Continue adding the other tip sections until the
antenna is complete.

20M5-125 ASSEMBLY MANUAL

10. Determine the BALANCE POINT of the assembled antenna and mount the BOOM TO MAST
PLATE using two 3 inch U-bolts, stainless steel lockwashers and nuts.

11. OVERHEAD BOOM SUPPORT SYSTEM.
A. Attach one end of the Dacron cord to the rear eyebolt using two turns around the eyebolt and a
series of three half hitches or equivalent knots. Without cutting the cord, secure other end at the front
eyebolt. Pull on the knots HARD to SET them and tape the excess cord back to main cord tightly with
black vinyl electricians tape. Seal ends with heat or flame to prevent fraying.

B. TEMPORARILY insert a standard 2” U-bolt through the turnbuckle plate and add two nuts so about
1/2 inch of the threads stick out. Insert U-bolt studs through the top set of 2” U-bolt holes in the boom
to mast plate from the boom side and add two more nuts. Open the two turnbuckles up until just a
thread or two from each end shows inside the body of the turnbuckle. Hook the turnbuckles into the
holes at the edge of the turnbuckle plate. Equalize the Dacron cord over the plate and cut it. Take two
wraps of the cord through the eye of the rear turnbuckle, PULL the cord as tight as possible and make
the knots as before. Repeat for the front cord section and turnbuckle. Cut off any excess over one foot
long and again seal and tape the excess cord back to the main cord.

C. Now DISASSEMBLE the U-bolt from the boom to mast plate. The guy assembly is now centered
and the turnbuckle plate ready to be installed to the mast and raised until the boom is straight.

If practical, after the final assembly and before installation, let the overhead guy system support the
boom and take a set overnight: Install a 2’ to 3’ temporary 2” mast section to the boom to mast plate
and attach and raise the turnbuckle plate. Support the antenna at the boom to mast plate. The Dacron
cord DOES NOT STRETCH UNDER LOAD but cord and knots will take a SET and the boom may
droop just a bit. Reset turnbuckle plate. If your boom droops again following this adjustment, check
your knots - they may be may be slipping. If an overnight set is not possible, then after installing
antenna on mast, lean on or pull on the cords to increase the tension and help the knots take their final
“set.” Make sure the knots are not slipping. When the guy system has taken a “set”, loosen the 2” U­bolt and adjust turnbuckle plate height until boom is straight and level.

After final installation, do any minor boom straightening with the turnbuckles. Then safety wire to
prevent changes to settings.

12. THIS COMPLETES THE ASSEMBLY. When the antenna is installed in position on the mast, the
main feedline can be attached and sealed at that time. REMEMBER to support the feedline at the
antenna boom and on the mast. Leave an adequate feedline loop for rotation around the tower. Mount
horizontally polarized VHF and UHF antennas at least 40” above or below this antenna to minimize
interaction.

CAREFULLY DESIGNED AND MANUFACTURED BY:

M2 ANTENNA SYSTEMS, INC.

4402 N. SELLAND AVE.

FRESNO, CA 93722

[phone] FAX: [phone]

www.m2inc.com Email: [e-mail]

20M5-125 DIMENSION SHEET

NOTE:

DRAWING NOT TO SCALE

20M5-125 ASSEMBLY DETAILS

GENERIC COMPRESSION CLAMP DETAIL

20M5-125 PARTS & HARDWARE

DESCRIPTION QTY

Boom sections, 3" x .125 x 15' swaged.......................................... 2

Boom section, 3” x .125 x 15’ straight ............................................ 1

Boom sleeve, 2-1/2 x 96" ............................................................... 1

Boom to mast plate, 8 x 8 x .250" (M2APT0070) .......................... 1

Element, 1-1/2 x .058 x 30" alum. tube SOE ................................. 10

Center Sleeve, 1-3/8” x .058 x 52” alum tube STR ........................ 4

Center Sleeve, 1-3/8” x .058 x 26” alum tube STR ........................ 2

Insulator, center 1-1/4” x 24” fiberglass (M2AFG0034).................. 1

Element, 1 -1/4 x .058 x 48" alum. tube SOE ................................ 10

Sleeve, 1-1/8 x .058 x 43.5” alum tube STR .................................. 10

Element, 1 x .058 x 48" alum. tube STR ....................................... 10

Sleeve, 7/8 x .058 x 32” alum. tube STR ....................................... 10

Element, 7/8 x .058 x 23” alum tube STR ...................................... 10

Element, 3/4 x .049 x 53” alum tube SOE ...................................... 10

Element tip, 1/2 x .049 alum. tube STR:( SEE DIMS.) ................... 10

Hair pin tubes 3/8” x 40”, bent ........................................................ 2

Balun, 1:1 COAXIAL ...................................................................... 1

Element Clamp Plate, 3 X 6 X 1/2" (M2AEC0041) ........................ 10

Machined Cradle, 3” LD, 1” x 4” x 1/2" (M2AMC0136) .................. 10

Turnbuckle plate, 2 x 5 x 3/16" (M2APT0110) ............................... 1

Dacron rope, black 5/16 x 36 ft. ..................................................... 1

Turnbuckle, forged 3/8" .................................................................. 2

Eyebolt, forged 3/8 x 6" .................................................................. 2

Band clamp 2-1/2 to 3-1/2 ss ......................................................... 1

Poly disc, 1-1/4” (M2ADI0020) ....................................................... 2

Cable ties, large ............................................................................. 3

U-bolt & Cradle, 3" ......................................................................... 2

U-bolt & Cradle 2-1/2 ..................................................................... 1

U-bolt & Cradle 2" HD .................................................................... 4

U-bolt & Cradle 2" .......................................................................... 1

Compression Clamp, 5/8” (M2AMC0145) ...................................... 10

Assembly Manual ........................................................................... 1

HAIRPIN PARTS BAG

Hair pin shorting bar 1/2 X 1/2 X 5.0 (M2ASB0262) ...................... 1

Hair pin spacer 3/8 X 1.0 tube ........................................................ 1

Hair pin clamp plate........................................................................ 4

Balun “L” bracket 1 x 1 x .125 (M2APT0016) ................................ 1

IN HARDWARE BAG

Bolt, 1/4-20 x 3-1/2” ss ................................................................... 4

Bolt, 1/4-20 x 3" ss ......................................................................... 20

Bolt, 1/4-20 x 2-3/4" ss ................................................................... 30

Bolt, 1/4-20 x 2 ss........................................................................... 8

Bolt, 1/4-20 x 2-1/2” ss ................................................................... 2

Bolt, 1/4-20 x 2-1/4 ss .................................................................... 1

Set screw, 1/4-20 x 1/4 ss .............................................................. 2

Nut, 1/4-20 locking, ss .................................................................... 43

Nut, 5/16-18 ss ............................................................................... 4

Lockwasher, 5/16 ss ...................................................................... 4

Nut, 3/8-16 ss ................................................................................. 14

Lockwasher, 3/8 split ring ss .......................................................... 14

Screw, 8-32 x 1-3/4" ss .................................................................. 20

Screw, 8-32 x 1-1/2" ss .................................................................. 20

Screw, 8-32 x 1-1/4" ss .................................................................. 20

Screw, 8-32 x 1/2" ss ..................................................................... 10

Nut, 8-32 locking, ss ....................................................................... 60

Nut, 8-32, ss ................................................................................... 10

Allen wrench 1/8 ............................................................................. 1

Penetrox cup .................................................................................. 1

20M5-125 ANTENNA PLOTS

FULL BAND PLOTS CW-LO FONE PLOTS