This blog was created to share my projects, ideas, and experiences in amateur radio with other operators around the world who also enjoy this wonderful hobby.

Wednesday, July 11, 2012

Dipole Antenna Construction Ideas

Step 1
The materials needed for the dipole antenna construction are shown above. We are going to use the dipole antenna center insulator built earlier. The other materials are, 26 feet of #12 or #14 stranded copper wire, two pieces of heat shrink tubing 1/4" diameter by 1- 1/4" long. The length of the wire sections is calculated using the formula ,468/F(MHz). Approximate wire lengths  for the popular Amateur Radio bands will be given at the end of the building process. The dipole we are about to build is for the 15 meter band. From the formula 468 divided by 21.0 mhz = 22.28 feet. Divide the result by 2 to get the lenght of each side of the dipole. The wires need to be longer to compensate for the connection loops and adjustments. Cut each side to 13'  to be safe.




Step 2
 Start by inserting one end of the copper wire thru the top of a crimping ferrule, then go thru the eyebolt, and back thru the bottom of the ferrule making a 2 inch loop. Move the ferrule as close to the eyebolt as possible, but don't crimp it. Crimping will be done later.



Step 3 
Insert a piece of heat shrink tubing thru the wire on the dipole center insulator. The length of the tubing is 1-1/4 " and the diameter is 1/4 ".




Step 4
 Now, strip about 1/2" from the insulation on the antenna wire and the center insulator wire. Apply 60/40
rosin core solder to both wires and wait for the solder to cool.



Step 5
 The next step is to insert each wire into the splice cap. It is a good idea to apply solder to the inside of the splice cap , this will make soldering  the wires easier. Apply solder to the splice cap and the wires . Do not crimp the splice cap over the wires because corrosion will damage the connection in little time, always use solder. This splice cap can take more than one wire so it is possible to build a two band or a three band dipole, with a single center insulator. Up to three antenna wires plus the center insulator wire will fit inside the copper splice cap. If #12 gauge wires are used it will only take two plus the center insulator wire. A larger diameter splice cap can be used if  # 12 wires are preferred for the construction.



Step 6
 Wait for the splice cap and the wires to cool and slide the heat shrink tubing until it covers evenly the splice
cap and the wires. Repeat the same steps on the other side of the antenna. It is a good idea to verify continuity of your connections with a VOM (volt ohm meter) or a DMM (digital multimeter) before applying
heat to shrink the tubing. Good quality electrical tape can be used instead of the shrink tubing as well as liquid tape (available at Home Depot) or silicone sealant.




Step 7
Now it is time to install the end insulators to each side of the dipole. The process is similar to the one explained for the center insulator ferrule installation. Do not crimp the ferrule on the dipole ends. This will be done at the end when you install and test the antenna with an antenna analyzer or SWR meter. The ends can be adjusted for minimum SWR by adjusting the length of the antenna wires. This is easily done on the dipole ends.
When the antenna is tuned for the operating frequency or frequencies, then you crimp both ferrules at the ends.The center insulator ferrules can be crimped after the previous steps are completed.



Step 8 
A close view of the crimp splice cap connectors used for the center insulator wire connections. The are made by Buchanan, the part number is 72400, the package contains ten pieces. They are available at  Home Depot for a few dollars. If the connectors are not available it is possible to solder both wire connections with a good quality 60/40 rosin core solder and then  protecting the connection with shrink tubing, electrical tape, silicone sealant or liquid tape. Remember, the idea of the splice cap is to fit more than one wire at a time, making it possible to build a two or three band dipole and at the same time protect the connection from the elements.


Step 9 
 The ferrules are made of aluminum, the internal diameter is 1'8". They will take #14 and #12 gauge copper wire. They look similar to a binocular ferrite core. They are available at Home Depot and other hardware stores. Four ferrules are required to complete the antenna, each package contains two ferrules. I have seen them  listed for sale on E-Bay also at fair prices.




Step 10 
 Bottom view of the ferrule package, the round barrels are not used. The ferrules are available in different internal diameters, so it is posible to build a lighter antenna for QRP, with #18 copper wire and a center insulator made with 1/2" PVC material and a BNC connector,  instead of 1" PVC material and a SO-239 connector. Also if larger diameter wire is needed, like #10 for example, a larger ferrule can be used to complete the antenna construction in the same way as with smaller diameter wire.



Step 11 
 A close up view of the aluminum ferrules. If bare copper wire is used for the antenna construction, like # 14 copper-weld, do not use the aluminum ferrules. Solder the wires from the center insulator directly to the dipole antenna wires with good quality 60/40 rosin core solder and protect the connection point with liquid tape or silicone sealant. If the ferrule is used with bare copper wire, a chemical reaction will take place between the dissimilar metals, destroying the connection in little time. Do not use any type of crimping terminal to make the connections, as the connection will deteriorate rapidly and a resistance will be created at the connection affecting your antenna performance.



Step 12
 This is how the center insulator looks with both dipole wires already soldered to it. If you haven't already checked for continuity, it is now the time to do it , before applying the shrink tubing to the splice caps.



Step 13
 Now, the shrink tubing pieces are in place. Use a heat gun, hair blower or matches to shrink the tubing. Be careful not to melt the wire insulation.


Step 14
 If a crimping tool is not available, use a large flat blade srewdriver to crimp the ferrules. Hit the ferrules with the screwdriver and a hammer along the center on both sides, until the ferrule is completely holding both wires. Do not hit to hard or you will nick or break the ferrule.


Step 15
The completed half wave dipole antenna. This one in particular is cut for the 15 meter band. Between twelve or thirteen feet of cable are used on each side of the antenna. Remember, do not crimp the ferrules at the end of the dipole until you install the antenna and adjust both sides, adding or subtracting to the wire at the ends. Use an antenna analyzer or SWR meter to adjust the dipole to the desired center frequency. Remember, making the antenna longer , lowers the resonant frequency and making it shorter, increases the frequency. The dipole is a balanced antenna, both sides must be equal in length, if you add wire to one end, add the same amount to the other and vice versa. When the SWR is set to an acceptable level, lower the ends of the dipole and crimp the ferrules. Surrounding objects, the height above ground and the antenna configuration ,(inverted vee, sloper, horizontal, vertical, etc.) will influence the size of the wire elements on your particular installation. That is why it is advised to always use one to two feet of extra wire on each end to tune the antenna. Don't let a long piece of wire hang from the dipole antenna ends as it will add to the total lenght of the antenna and fool your adjustments. Wrap the excess wire over the antenna wire backwards, when you are satisfied with the tuning, crimp the ferrules and cut the extra wire on both ends. From the half wave antenna formula 468/F(MHz) remember the result is the total wire length of the antenna, divide the result by two and add one feet of wire to aid in the tuning process. That said, you will need two 10' sections on 10 meters, two 13' sections on 15 meters, two 18' sections on 20 meters, two 35' sections on 40 meters or two 70' sections on 80 meters to build a half wave dipole antenna for your band or bands of choice. If you have any comments or questions about the dipole antenna construction process or need technical help with your particular application, please contact me via e-mail. I hope this information helps other amateurs take the challenge and build their own good quality half wave dipole antenna, saving money and learning at the same time.



3 comments:

  1. Thank you for creating this page! Very well done. You show very well how easily one can make their own antenna in a very affordable manner. I will be pointing anyone and everyone who says they can't make an antenna, or it's too expensive.after reading this they will surely come away with newfound excitement and enthusiasm for the hobby. Thanx again, W1LEB Larry

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  2. I've used what I've learned from your page to build my own antenna. The pictures of the parts (like aluminum ferrules and crimp splice caps) were very helpful in knowing what to buy and where to find them. Thank you for a well-done presentation! AE9Q Dave

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