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.