5 Element 20m Wire Beamat

WB6DCO

Construction of an East facing 20m beam made from wires supported on both ends by fiberglass

poles.

August 2009Joe Perry Jr.

20m Beam Yagi Designs

• I found two Yagi beam design programs

• I ran the standard 14.100 MHz Yagi beam with all the same size elements of wire for 0.125” in diameter.

• Most beams are larger tube designs

Design Software's

• Java and Dos programs are out there for Yagi Design. But what is behind the software? You don’t know.

• They generally have an Optimize or Auto or Best Gain analysis.

• The Spacing of the elements can change quite a bit between the types.

5 Wire Beam Design at 14.1 MHz

Pretty Beam

Wire Beam Layout Lengths

Each wire supported by 12 foot fiberglass poles screwed to roof edge 12 feet up from the ground.

30’2” long

31’ 5” long

32’ 8” long

17’ each side

35’ 7” long

Spacing 10’ 4”

Spacing 7’ 5”

Spacing 11’ 7”

Spacing 15’ 8”

You can’t get any Uglier!!

The Driven Element

• The Driven Element (Dr.) is a flat Dipole setup.• The driven element of a Yagi is the feed point where

the feed line is attached from the transmitter to the Yagi to perform the transfer of power from the transmitter to the antenna.

• A dipole driven element will be "resonant" when its electrical length is 1/2 of the wavelength of the frequency applied to its feed point.

• The feed point in the picture next is on the center of the driven element.

Driven Element PhenolicThese plastic antenna holders are available on Ebay and HRO…etc.. About 10$ a piece. They make Dipoles and Inverted-V’s easy. The connectors come in PL259 and N molded units. The fiberglass poles are each 44” long and cost 60$ for a set of 12.

Let’s Resonate the Astronack

• I put up the Driven Element ( Dr ) by itself first. I then attached 50 feet of LM400.

• The MFJ-269 Null Meter showed this:• Freq SWR loop-back length

• 13.50 MHz 2 1.5”• 13.61 1.5 3.0”• 17.73 1.2 6.0”• 13.98 1.2 12”

• 14.26 1.0 17” • The last length shows Xs=1, Load Rs=49 ohms

Wire ends loop Back

• What is the effect of the extra wire on the end of the Driven Element when you have to loop it though the egg insulator and back over the main wire?

• I would say that the wire length goes through the egg insulator around the loop back until the wire shorts to the main wire again?

The Reflector is more important

• The reflector is the element that is placed at the rear of the driven element (The dipole). It's resonant frequency is lower, and its length is approximately 5% longer than the driven element. It's length will vary depending on the spacing and the element diameter. The spacing of the reflector will be between .1 wavelength and .25 wavelength.

• It's spacing will depend upon the gain, bandwidth, F/B ratio, and side lobe pattern requirements of the final antenna design.

Lets Add the Reflector Wire

• I put up the 35’ 7” Reflector Element 10’ 7” West of the Driven Element.

• Remember the Dr is now at• 14.26 MHz SWR=1 and Xs=1, Rs = 49 ohms. This is at

its best.• After a Reflector wire is added we see this:• Freq MHz SWR Load Rs• Before finding a new null the SWR and Rs changed:• 14.26 1.3 37 ohms• Null moved down frequency to:• 14.086 1 51 ohms, Xs=3

The Director(s) don’t count• The director(s) is the shortest of the parasitic elements and this end of the

Yagi is aimed at the receiving station. It is resonant slightly higher in frequency than the driven element, and its length will be about 5% shorter, progressively than the driven element.

• The director(s) lengths can vary, depending upon the director spacing, the number of directors used in the antenna, the desired pattern, pattern bandwidth and element diameter.

• The number of directors that can be used are determined by the physical size (length) of the supporting boom needed by your design.The director/s are used to provide the antenna with directional pattern and gain.

• The amount of gain is directly proportional to the length of the antenna array and not by the number of directors used.

• The spacing of the directors can range from .1 wavelength to .5 wavelength or more and will depend largely upon the design specifications of the antenna.

Now pop up the 3 Directors

• I put up all 3 Directors at one time in front of the Driven Element with Reflector already installed.

• Freq SWR Rs Xs• Was: 14.086 1. 51 3 without retuning we now see:• 14.086 2.5 33 22 retuning to find the new null we see: 14.320 2.2 89 21This is now higher in frequency than the 14.100 I

would like, so we have to adjust something?

Re-adjust the Driven Element

• I tried changing the Dr element lengths to bring the null with all 5 elements down to 14.100 Mhz.

• I let out from each end loop of the Dr 3”• After retune:• 14.102 MHz, SWR 1.6, Rs 81 ohms, Xs

12• This is not what I would say a good null for

a beam.

Nothing is perfect in life

• We can see that the Load Resistance changed each time we added an element.

• When I added the reflector element to the dipole Dr the Null changed from 14.1 down to 13.5 mhz.

• So I had to shorten the Dr elements by 17” to get it back up to 14.1 MHz null.

Darn Directors !!7734!!

• So you want change you get it…. The Reflector caused the Frequency of the dipole null to move down frequency.

• Now the Director Elements are shorter than the Dr in length and they all caused the Dr frequency to go up.. To 14.350 now..

• So, I had to lengthen the Dr element lengths by 3” to get it to null near 14.1 mhz.

• The SWR is not great but I don’t know what to change to fix it better.

Give or Take Garage Door, Tower, Power Lines, and Wires

• Now I nulled the Dr by itself when I started, so this took into any effect the garage wiring, metal roll up doors, tower, machinery, guy wires, etc...

• Then adding of the reflector did just what theory says..forces null frequency down<

• Then adding of the directors did just what the theory says..forces null frequency up>

Spacing of Elements

• I can add more of the 2” fiberglass poles to raise all the wire ends until the poles get to wobbly or the screws won’t hold them up.

• Raising the Dr will lower the Rs resistance load they say?

• Making the feed line LM400 longer also raised the resistance of the load. I had cut the LM400 from 50’ long to 25’ long just before I put up the reflector element. The Rs changed from 50 ohms down near 33 ohms.

Bandwidth Control if any

The impedance of an element is its value of pure resistance at the feed point plus any reactance (capacitive or inductive) that is present at that feed point. Of primary importance here is the impedance of the driven element, the point on the antenna where the transfer of rf from the feed line takes place.

• Maximum energy transfer of rf at the design frequency occurs when the impedance of the feed point is equal to the impedance of the feed line. In most antenna designs, the feed line impedance will be 50 ohms, but usually the feed point impedance of the Yagi is rarely 50 ohms. In most cases it can vary from approximately 40 ohms to around 10 ohms, depending upon the number of elements, their spacing and the antenna's pattern bandwidth. If the feed line impedance does not equal the feed point impedance, the driven element cannot transfer the rf energy effectively from the transmitter, thus reflecting it back to the feed line resulting in a Standing Wave Ratio. Because of this, impedance matching devices are highly recommended for getting the best antenna performance.

•The impedance bandwidth of the driven element is the range of frequencies above and below the center design frequency of the antenna that the driven element's feed point will accept maximum power (rf), from the feed line. 

• The design goal is to have the reactance at the center design frequency of the Yagi = (0),,, (j + 0).

• The impedance matching device will now operate at it's optimum bandwidth. Wide element spacing, large element diameter, wide pattern bandwidth, and low "Q" matching systems will all add to a wider impedance bandwidth.

I used the MFJ-269 to test• If you want to borrow it let me know. It does LF/VHF/UHF antenna, coax, wire, etc…• Joe 760 373 4290• It uses N connectors• or with N to PL239 adapters• Covers:• 1.8 MHz to 170 MHz• UHF 415 to 470 MHz• Battery portable

Wire Beam Results

• Since the 20m band is not that good this year I don’t have good results yet.

• I have listened with my Kenwood Ts140 and been able to hear stations on the east coast. My other dipoles and inverted-V alone did not seem to pick up the East coast.

• The 5 wire beam seems to have hot directions, toward Wisconsin, and toward Alabama.

• I talked with about 100 watts to Wisconsin easily and to Alabama.

• I am listening to hear Europe Stations reflect into the wire beam.

Feed Point Resistance for Dipole

14.1 MHz 10 foot above Ground, Take-Off Pattern Driven Element as

Dipole alone

14.1 MHz 20 foot above ground Take-Off Pattern Driven Element as

Dipole alone

14.1 MHz 40 foot above ground Take-Off Pattern Driven Element as

Dipole alone, best height

14.1 MHz 60 foot above ground Take-Off Pattern Driven Element as

Dipole alone

5 Wire Lobe Pattern?

I have a field strength meter to see the pattern like ½ mile away?

I am only 24 feet up so I think the Pattern is very is very flat but step take off angle.

I hear NNE and I hear SSE but I don’t hear in the middle due East? So,

Analysis with eznec.exe

• I down loaded the version 5 demo package for the eznec antenna pattern analyzer.

• They have many demo antenna with the program.

• So I started with the Dipole for the charts before this series.

• I will now do Dipole + Reflector• Then Dipole + Reflector + Directors(3)

Dipole + Reflector 10 dBI gain, F/B 10 dB, side view

Reflector + Dipole + Director1 has 10 dBi Gain, F/B 14 dB, side view

Refl + Dr + D1 + D2, 12 dBi gain, F/B 14 dB, side view

Lastly the whole beam, 12 dBi gain, F/B 13 db at 20 feet up, side view

3D top view of beam 20’ up, looks like a single full lobe to East

The whole wire beam 40 feet up, side view, what’s that bump!

Shall we try for 60 feet up? This is crazy stuff.

Oky, 60 feet up note the extra top hat?

Wire Beam with Reflector Decentered at 60 feet up in the air

I decentered the Reflector by 20” left of center. No remarkable changes noticed in the lobes plots.

As long as you move the elements horizontal you don’t see any changes for at least 20” off center line.

Move the Reflector to Dr spacing

I will now move the Reflector out to half wave length behind the Driven Element and then step the Driven to Reflector spacing distance to see if any Gain or Losses.

192” Gain 13.4 F/B 4.73

162“ Gain 13.7 5.12

163“ Gain 14.0 5.46

123” Gain 14.0 5.56

100” Gain 14.1 5.8

60” gain 14.2 6.26

Not much effect in moving the wires in and out.

• If you look at the plots the effective launch angle seems to change more than the Gain.

• The launch angle goes down as the beam goes up in the air.

• 20 feet launch angle is 30• 40 feet 22• 60 feet 16• This makes some since. So if you want to get

the farthest reflections you can? What angle do you need????? Anyone got this one?

Notes from a book, “Ionospheric Radio” by Kenneth Davies IEEE

Components of the Wire Beam• I used a Bud Wig HQ-1 type feed line insulator. They come in PL239 and N connectors:

• Bud wig Company, Inc. 9692 Via Excelencia, Suite 103 • San Diego, CA 92126 USA Phone: (858) 549-5050 • Fax: (858) 549-2020 • Email: budwig@aol.com • www.budwig.com

The Delta-C looks pretty good also.

Model SEP Arc-Plug™ Static Electricity Protector is a special gas tube component designed to “bleed off” slow rising static electricity buildup of the kind generated by thunderstorms, high wind driven snow or sand or by a harmless looking cloudy day. These static charges have been measured to several thousand volts and can damage or destroy sensitive components in receiver or transceiver front end circuitry.

Field Strength Meter I ordered. Covers 1 MHz to 8 GHz

Field Strength Walk Around

• Here are some dBm signal levels as I walked around the California City block in front of the 5 wire beam output.