Build a beam for 6 meters

Design by W4DEX and built by N4DBM


Tools and Parts Needed

1 - Drill or better yet a nice stable drill press
2 - Bits the following sizes (1/8) (1/4) (3/8) (1/2) inch drill bits
3 - Four TV mast U-bolts and saddles that fit 1.5" conduit
4 - Four pieces (10 feet each) of 1/2 inch EMT conduit
5 - One piece of 1.5 inch conduit EMT
6 - One flange mount SO-239 (Radio Shack) or get fancy and use a type-N connector
7 - One foot of RG-213 coax
8 - Assortment of stainless bolts and nuts (1/8 inch threads) you will need about 4 sets
9 - One piece of 3/8 inch aluminum tubing about 18 inches long (old TV antenna perhaps)
10 - One aluminum "L" bracket or angle, about 2" by 2" (use whatever you have)
11 - Soldering iron with big tip for soldering RG-213 center to SO-239.
12 - No-Oxide grease (optional) or some other form of good electrical grease
13 - Center punch and hammer unless you can start drilling without the bit walking
14 - 10 inch long by about 1 inch wide aluminum strip (cut from old license plate or road signs)
15 - Tubing cutter or hacksaw and file

You will be using a gamma match to feed the antenna here. If you wish to feed it some other way then by all means do so. Using a "T" match will probably have a cleaner pattern for horizontal polorization. But the gamma match is a little easier. The dimensions are for 50.5 MHz which is SSB/CW part. The antenna will have about 2 MHz bandwidth for VSWR under 1.5:1. Cut the 1/2 inch EMT for the following lengths.

REFLECTOR - 115 inches
DRIVEN ELEMENT - 109 inches
1st DIRECTOR - 100 inches
2nd DIRECTOR - 98 inches





The elements are actually spaced 39" from center to center of conduit. It isn't super critical. with the spacing used, four elements will take up almost every bit of the 10 foot boom. Instructions: Cut each element according to picture and label them. Divide each lenth by 2 and mark the center of the element. You are using the 1/2 inch EMT for the elements by the way. Next, get one of your TV mast clamps out and space the U-bolt accordingly and mark the holes. You will be drilling completely through the conduit. Drill the holes with a 1/4 inch bit. It will be a tight fit because the U-bolts are 1/4 inch, but you ought not drill out any more than you need as it will weaken the operation. Do this to all four elements and make sure your U-bolts fit through as labeled in the picture below.



Next you will need to mount all elements on the 1.5" boom. Then start on your gamma match. Get the aluminum angle and drill a hole with the 1/2 inch bit so that you can mount an SO-239 or Type-N connector through it as shown in the picture below. Make 1/8 inch holes so you can use the stainless screws to secure the connector. You ought to be able to mount it so that the flange is on the outside where you will be attaching your coax. You can saw off the edges and make it look a little more professional if you like but it won't make any difference electrically. Drill 1/4 inch holes in the bottom of the angle so that it will match up with the U-bolt you are using for the driver.






Now work on the gamma match. Take the RG-213 or RG-8, something with SOLID type dielectric which will not absorb water. Strip the shield off and and then pull the braid and jacket off leaving you with the center conductor and dielectric. This should fit snug, but able to move, inside your 3/8 inch aluminum tubing. You have just made a very low value capacitor which you can tune for the best match (SWR) once you get it finished.



The aluminum strip must be bent around the gamma match rod and the driven element very carefully to ensure about a 2 inch spacing between the two. It is usually best to bend a nice loop around the 3/8 tubing first then bend around the 1/2 inch driver. It helps to have some sheet metal tongs but can be done with a vise or even a big set of pliers. When you get the pieces bent make sure you have it so you can't mash the ends completely together. You want about 1/8 inch so that you have room for the screws to tighten. Drill holes where the screws will be as in the next picture. Use stainless hardware if possible.



If you want to make the match more mechanical sturdy, you can take a piece of plastic, or even treated wood about 1/4 inch thick and drill 1/2 inch and 3/8 inch holes and make it so that it provides for means of support close to the connector. If you don't do this then you are relying on the strength of your solder joint on this end. A bird will break it off. If you choose not to use an additional support like pictured below, then mount the antenna so the gamma match is down, and birds can't set on it.



I forgot to tell you that you will need a mounting bracket of some sort. This will be an additional $8.00 for more Radio Shack U-bolts and you will have to find a plate to drill holes in, making means for mounting the antenna to a vertical support pipe. This plate was from a big side mount kit.



TUNING THE ANTENNA - Try to get a mast of about 10 feet. Put the antenna up in the clear away from as many objects as you can. Hook a radio up on CW, AM or FM through a good dependable watt meter for VHF then to the antenna. Look at reflected power at the operating frequency. If it is high, loosen the aluminum strip and move it one way or another, about 1 inch at a time. If the SWR increases, move it back to its original position, then move it yet another inch in the opposite direction. It's a game of trial and error. I do not like gamma matches they are a pain in the butt. You will soon hopefully have a good match. I got this one to match with 40 watts forward, and 0.05 watts reflected! Beware that if the antenna is close to the ground or a metal object, your resonant frequency will decrease (you may see the best match at 49 MHz if it's close to the ground). Then you get the gamma match set properly, mark the strip and the tubes. Place grease in all places that metal will contact to prevent corrosion. Reinstall the gamma match and make sure again the SWR is good. Spray the U-bolts with clear Krylon or equivalent to prevent rust. Now you have a good four element beam with gain probably +/- 6 dB over a dipole.