8.5 DB gain for less than $40.00

10.8 DB gain for less than $50.00 by adding the 5th element.

SPACING is based upon 0.15 - 0.31 wavelengths, although I generally use 0.2 - 0.25.
The K constant is 492 for the REFlector, 492 for the DRIven element and 462 for Director2 and 460 for Director1 (457 for Director3 if added).
Remember that there is a FREE TO USE software program that implements these same formulas and takes a lot of the guess work out of design. The link is located lower in this text.

The feedpoint will naturally be 72-75 ohms. After all most designs use a DIPOLE MATCH system and while most Ham's are more familiar with a DIPOLE, this is not the best way to match a parasitic array. What tends to happen is based upon any DIPOLE in free-space. As soon as we add elements and adjust height off ground the Dipole match tends to change impedance and we come away with an antenna that may be difficult to tune, especially while up on the roof or tower. While on the ground it seems perfect, put it in the air and it just ain't the same. Remember that additional elements will change the center of balance and that places the driven element further away from the main mast center point. Adjusting a DIPOLE element on the tower is damn near impossible.

The GAMMA match will make things a lot easier to tune. If you read my article on the LOW BUDGET 10 Meter Beam that I built, you should understand this design. The Gamma Match is basically a CAPACITOR tunes a L/C circuit. The ARRAY is the L and the GAMMA is C. I do not use a physical component but simply 2 pieces of aluminum tubing that is available at any ACE Hardware (or Home Depot). On the 6 meter beam, I started with 5 inches of 3/4 OD ("see text") thin wall tubing. Next I slide, inside the 3/4 inch tube, a piece of 1/2 ID clear vinyl hose. Now, Inside that I slide a 29 3/4 inch piece of 1/2 inch OD aluminum tube. The vinyl tubing gives me the proper insulated spacing gap for a capacitor that will tune perfectly and handle a full 1000 WATTS. In the image above the GAMMA LENGTH is element LEN/3.8 while the spacing below the DRIVEN ELEMENT is LEN/35. The formula actually takes into consideration the length of the driven element (L). The Capacitor pF is the result of the formula C=2400/F MHz or about 45 pF. However, don't get fancy with the formulas, get out in the yard and tune the GAMMA to your frequency of choice. If the match is not correct, slide the small tube in or out of the large tube. Trail and error using an SWR bridge will work fine but an MFJ Antenna Analyzer will get you on the money first time. You can tune the driven element to a near perfect match while only six feet off the ground and without the other elements in place. The GAMMA length should be LEN/3.8 and spacing should be LEN/35. (TAKE NOTE) The single most important dimensions on the array will be the Reflector, Driven element and Gamma length.

To ease the pain...just forget all this math and build the GAMMA the way I explain, tune for resonance on or near the frequency of your choice and use my boom/element lengths and spacing. You can't go wrong.

The antenna construction is simple. Attach the elements directly to the boom. Be sure to sand away a little of the coating on the conduit. This will insure a good electrical connection throughout the beam. (You can primer the beam later or paint it RED just to nut the neighbors.) Use your VOM to test continuity all along the beam. All elements should be connected electrically together. The GAMMA MATCH is insulated from the boom at one end, where the coax center conductor is attached to the OUTSIDE 3/4 INCH ALUMINUM TUBE (I call this the STATOR). The insulator can be anything like plastic, Lexan or Ceramic. The short is just a flat piece of aluminum or copper, makes no difference as long as it is sturdy and will not flop around. Now to tune the GAMMA simply slide the 1/2 inch tube into the 3/4 inch tube, use the analyzer and bring the driven element to resonance. I do this with the BOOM in place but no elements. If you build the antenna using the dimensions as shown above, you should be close, if not right on, at 50.125. You can shorten your dims and move up the band, however, 50.125 is the DX calling frequency and most of the action will be within 25- 50 KHz of that frequency.

Parts are easy to obtain. Purchase 4 or 5 - 10 foot lengths of 1/2 inch conduit and 2 - 10' lengths of 1 1/4" galvanized fence post. The 18 Ga. fence post is about $8.75 each at ACE and the 1/2 inch conduit will be somewhere around $2.35 for each 10 foot length. The beam will weigh about 9 pounds depending on the hardware you use to attach the elements.
I use 1/2 by 1/2 inch aluminum channel (3 inches long). I notched the 3 inch piece of aluminum to fit around the 1 1/4 inch boom. Then I attached the element using 2 - 1/4 by 2 1/2 inch stainless bolts. Drill through the element on center and spaced at 1 1/2" c-c. You can buy this material at most ACE Hardware or Home Depot stores. It comes in a 36" lengths and you simply cut 10 - 3" pieces (2 for each element). You can also purchase "C" clamps with the correct dimensions, but this will make your beam more expensive and these hardware clamps tend to rust after a while.
 

Building the beam is "not rocket science" and the result is a great beam that is rather broad and has a tested F/B ratio of 12 ++ DB with a 10.8 (5 element) or 8.6 (4 element) DB forward gain at 25 FEET above ground. Use any cheap rotor and don't be too concerned about brakes, this beam does not have a very large wind load. Yes you can add more elements. Use the Java program below to get the best spacing. Start the element calculations for additional directors at 10% less and about 48 inch spacing (adjust from there).

Watch for more on this beam as I tune and work to make it a better performer...see you on 6 METERS. I will continue working on this article so you can obtain the best performance out of your antenna. I remind you to pass this along to all hams who want a 4 or 5 element 6 METER beam for under 50.00. This is the American way...No, I ain't buying the beam for you...this is not SOCIALIZED HAM RADIO...it is a hobby and if you have the bucks to buy really fancy new stuff...do it!! But if you are on a budget like me, you build...K3HKR Thanks
 
Here is a great YAGI design website: YAGI MODELER will require JAVA on your machine.
NOTE: I will attempt to offer my own modeler program as soon as I become a little more proficient coding in JAVA.

Save and print this DIMENSION CHART:
The commercial 6 METER beam will cost about 149.00. You can build this beam using 1/2 inch conduit for somewhere around 30 bucks...The 5 elements should run you 15.00 total and I cannot imagine the hardware including the GAMMA costing you any more than 15 - 20 at most. So go ahead and jump in on 6 meters. Most of today's modern transceivers offer 6 Meters as an option; while on all new Kenwood radios (TS-480 - TS-2000), 6 meters is standard equipment. Hint: Do not purchase a new HF radio that does not offer 6 Meters.
 

                                     USE THIS DIAGRAM FOR ANY BEAM DIMENSIONS ON ANY BAND.

Spacing Reference: REF to DRI = 44", DRI to D1 = 53.125", D1 to D2 = 59.5" and
D2 to D3 = 48" for a TTL of 202.5" over all. GAIN: Estimated at 11 DB + or - .3 DB.
Element length: REF = 116, DRI = 113, D1 = 107, D2 = 104, D3 = 103
NOTES: If you use the YAGI MODELER you can play with these dimensions prior to building. You may find a few more DB's hanging around in the ELEMENT LENGTH dimensions. But remember that over all total lengths will not change the GAMMA settings by very much. So remember to tune the GAMMA for best SWR, without all the elements, which should result in a 1.2:1 or slightly higher at 50.125. If your SWR PLOT changes after you attach the elements you should check the length of the Reflector if the settings go lower in frequency...or the length of Driven element if plot results go higher in frequency. The directors should not effect the SWR PLOT.

 

NEXT:

THE 2 ELEMENT 20 METER WALLET BUSTER:

Here are the basic details: I am building this now and you can watch it grow.
UPDATE: 09/06/09 - Tuning the GAMMA: As of this date we are at 1.3:1 and I believe I need to change the GAMMA tube distance from element or shorting bar position.. I will not release dimensions until I get it near 1.5:1 (FYI).
DESIGN: Design program YagiModler Applet(a Java based application).
As of this writing: The GAMMA TUBE is a 53" aluminum tube (1/2 OD) inserted into the 8" GAMMA HAT (3/4 OD) to 6".
(47 inches of the GAMMA TUBE remains below the beam)
The SPACING - driven element to GAMMA TUBE should be 5.75" and the SHORTING BAR should be 39.5 inches from CENTER of ELEMENT.
It should look like this: The 2 ELEMENT BEAM should have a 50-54 ohm impedance at resonant frequency (X=0)
SEE TEXT:
The 3/4 inch GAMMA HAT should be 8" long. There is no calculation that I have dreamed up. I simply use my MFJ Analyzer and adjust till it all fits. There are a couple of rules you should follow: (1) The shorting bar should never be more than element length in inches divided by ten. (2) On 20 meters the ELEMENT to GAMMA spacing should be 5 inches INSIDE - INSIDE.

This is a good starting point. The element SWR comes in at 1.0:1 at 14.250. That is close enough for me so I will next add the BOOM and Reflector. I still believe it should be 396.75 inches. But because the BOOM and REFLECTOR are not part of the array circuit, this might all change as I finish the beam construction.

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Two element close spaced on a 96.5 inch boom.
Driven Element = 404.5 inches LONG
Reflector = 414.125 inches LONG
Material - Aluminum Tubing.
Match - Gamma (see above). For gamma design and construction click here.
Cost - Estimate: $79.00 based upon MFJ thin wall aluminum tubing estimated price (shipping not included).
Boom: 1 1/4 Fence Post 18GA. (9.00)
In the Pattern image...The RED plot is the beam we are building. Note the 10 DB gain circle is BLUE and the 0 DB gain circle is GREEN. This is a rather reasonable amount of gain on 20 when considering the spacing used. Running 500 WATTS SSB will certainly be heard just about anywhere if conditions are good to decent. Have fun...more coming soon.

Final design and testing at ground level. (09/10/09)
Final Build and ground testing. (09/15/09)
The element length has changed but the DB gain is now 7.25 at 14.050. The actual "X=0" value fell in at 14.270 and that is at 10 feet off the ground. The GAIN is 6.6DB at resonant frequency with a IMPEDANCE of 52 OHMS and a 1:1 SWR. The L4B loves it and tunes very low with little or no trouble at all. I eventually had to lengthen the elements by 2% and shorten the GAMMA TUBE and GAMMA SHORTING BAR.
This is where it will be set for the roof tower.

Next: How does it work ???


GAMMA CONSTRUCTION ALL BEAMS:
The GAMMA CONSTRUCTION is simple. The GAMMA HAT is 3/4 OD tubing, the GAMMA TUBE is 1/2 OD tubing and the INSULATOR (capacitor spacer material) is 1/2 in. ID VINYL TUBING used for AIR PUMP HOSE and several AUTOMOTIVE APPLICATIONS. You can find this at most any ACE HARDWARE. This spacing will allow you to run a kilowatt with no chance of arcing. If you seal the ends of the tubes with RTV that will eliminate SWR effects from moisture. The SHORTING BAR should be aluminum and at least 1/2" wide (by dimension given). The INSULATED STRAP can be made of 1/8 or 3/16" LEXAN bar stock. Always use a good coating of NON-OXIDE BEAM GREASE.

This simple, yet very effective design will replace the need for large variable capacitors mounted at the boom near the driven element. The VINYL TUBING if fitted properly will allow 1KW of RF without breaking down and arcing over.

Now a little about HOME MADE GAMMA match systems. I have read more negative posts on blogs and message boards that all claim the GAMMA is dead...Not true. If you understand the principal you will have no problem making a GAMMA work well and yes, over a broader range than a DIPOLE match. Rule of thumb...the more elements on the boom the lower the impedance at resonant frequency. Therefore a 2 or 3 ELEMENT BEAM on 20 METERS should have an impedance that will match 50 ohm coax very well. My 5 ELEMENT BEAM on 6 has a 42 OHM Impedance at the GAMMA and again, 50 OHM coax works very well.
Reasons for having problems tuning GAMMA MATCH antennas range from poor design, bad math, incorrect capacitor and on and on...Using the construction method above you create a LARGER CAPACITOR and have more room to adjust than using a VARIABLE or FIXED cap in series with the GAMMA ROD.
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First: Divide the DRIVEN element length by 10 and that is where the SHORTING BAR should be at reference. Never start with this measurement shorter than above. The SHORTING BAR position is critical and I am sure that any one who has had problems in the past, could have cured them by adjusting the SHORTING BAR to reference.
Second: The measurement in between the GAMMA ROD and the ELEMENT should start at 6 inches at 14.0 and graduate to 3 inches at 50.4 MHz. Use the Excel plot I show below.
Third: The GAMMA HAT requires a minimum of 9.75  inches in length at 14.0, while at 50.4 MHz I have used as little as 3.5 inches of 3/4 tubing.
Finally: When adjusting the GAMMA TUBE into the GAMMA HAT you should keep in mind that this is a capacitor and the LESS the TUBE is inside the HAT the lower the capacitor value will be. When adjusting a GAMMA use your analyzer and above all...ADJUST ONLY ONE ITEM AT A TIME !!! Take notes and maintain a good reference plot.

This design works, and unlike removing shield from RG8 and sliding the core inside a 3/8 tube, using aluminum 3/4 tubing over 1/2 tubing creates a larger capacitor value with greater adjustment resolution and almost no (zero) VSWR weather related issues. The tube on tube design eliminates mechanical stress problems and offers greater strength over all. This ain't bull-shit...this GAMMA works. I have built more than a dozen beams using this system and not one was ever thrown away because it could not be tuned properly.

Have questions...contact me.
Thanks, Terry - K3HKR