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.

Sunday, July 8, 2012

Dipole Antenna Center Insulator Construction

step 1

The materials needed for the construction are, one 1" pvc cap, one 1" to 1/2 " pvc reducer adapter, one SO-239 chassis mount connector, four #6 sheet metal screws, three # 8 eye-bolts ,three flat washers, three split washers, six # 8 nuts and two pieces of # 14 gauge stranded copper wire, six  inches long each. I decided to use all stainless steel hardware for the construction, but zinc plated hardware can be utilized if desired. Remember that rust resistance is the advantage of using stainless steel versus zinc plated hardware. All material, except the SO-239 connector were purchased at a local Home Depot store.

step 2

Now you need to mark the location of the four  holes on the SO-239 to the 1/2 " side of the pvc reducer adapter and the top and side holes on the pvc cap. A 5/32 " drill bit is used for the three pvc cap holes and a 3/32 " drill bit for pvc reducer adapter holes. I used a drill press to make sure the bit stayed through the pvc material all the way, especially on the reducer adapter. If using a hand drill, care must be taken to ensure you drill all the way through the pvc reducer wall material. The depth of  four holes must be adjusted to a half inch.

step 3

This is how your cap and your reducer look after drilling. On the cap it is very important to center your drill bit on the top the best you can before drilling, a pilot hole can be made with a sharp nail to keep the bit from moving away. The side holes on the cap must be facing each other. Both holes are  1" above the open end of the pvc cap.

step 4

The correct sequence for the eye-bolt hardware assembly is shown. One of the nuts remains on the outside of the cap on all three eye-bolts  Inside the cap insert the flat washer first, then the split washer and the nut. Tighten the nut inside with a  long nose plyer, and then tighten the nut on the outside securely. 

step 4 b

This is the inside view of the pvc cap after all three eye-bolts are installed. Make sure the three nuts and the eye-bolt  threads do no touch inside the cap. I always keep the excess thread toward the outside of the cap. Sealing the cap up to the side eye-bolts with epoxy, silicone or hot glue is optional. If a 5/32 " drill bit is used you will notice that the eye-bolts make their own threads on the pvc material when installing them. In my opinion, sealing is not necessary.

step 5

Now it is time to solder the wires to the SO-239 connector. Before soldering it is a good idea to file around the center pin and along one side of the SO-239 close to the insulating material with a flat file to remove the nickel plating of the connector. This will help the soldering process. Remember , if using a 40 watt iron or soldering station, it will take several minutes for the exterior of the connector to heat up enough for the solder to flow. If you use a higher wattage soldering iron or soldering gun, care must be taken not to apply too much heat or you will end up melting the dielectric material of the connector. Always use good quality 60/40 rosin core solder and keep your soldering iron tip clean , never use acid type solder or paste flux on these connections

step 5 b

A side view of the SO-239 connector after both wires are soldered. It is a good idea to apply a little solder to the tips of both #14 gauge wires. Cut out about 3/8 " of the insulation on both wires, do not apply excess solder to the wire going on the center pin of the connector or it won't fit inside. Please allow enough time for the connector assembly to cool before continuing to the next step.

step 6

Using a hacksaw, cut the pvc reducer adapter, leaving 1/2 " of  the pvc material going into the cap.

step 7

Install the SO-239 connector using the four # 6 sheet metal screws. Tighten securely until the body of the connector sits flat against the pvc reducer adapter.

step 7 b

This is how the pvc reducer adapter looks from the inside after installing the SO-239 chassis mount connector. Sealing the connections up to the top of the reducer with epoxy, silicone sealant or hot glue is recommended. If hard epoxy is used, the center insulator can not be repaired in the future if needed. Replacing the wires or the SO-239 connector will require a new bottom assembly.( reducer adapter, SO-239 and wires)

step 8

In this step, drill two extra holes below the two side eye-bolts with a 1/8 " drill bit. Route the two copper wires outside the pvc cap ,as shown. Continue moving the bottom assembly upward while pulling the wires, each side at a time, until the reducer adapter is almost touching the pvc cap. Apply pvc cement and fully insert the adapter into the cap.  Pull both wires to make sure they are tight on the inside. Instead of using pvc cement it is also possible to use two # 6 sheet metal screws or rivets to secure the bottom part to the pvc cap. This makes it easier to make repairs on the center insulator in the future. (new wires, new SO-239,etc) Make sure if you decide to do this, that you drill the pvc reducer adapter perpendicular to the SO-239's sides, otherwise there is a chance of hitting the connector mounting screws.

step 9

The completed dipole center insulator after securing the bottom pvc reducer with the SO-239 connector to the cap. Using a VOM (volt ohm meter) or DMM (digital multimeter) check for continuity or shorts between the connector and the copper wires. In a future blog entry, I will show how to connect the antenna wires to the center insulator and to the end insulators completing the dipole antenna construction. There are many dipole antenna construction articles on the internet, magazines and antenna handbooks. This center insulator, especially if the stainless steel hardware is used, will provide many years of service near salt water. In my experience zinc plated hardware is cheaper, but won't last as long as stainless steel. Keep that in mind when deciding which one you will use in the construction of your outdoor antenna projects. If you have any questions about this project or any other antenna or amateur radio related matter, feel free to contact me via e-mail. I hope this antenna center insulator project help others decide between buying or building their own dipole antenna.


  1. Thanks for the instructions. I used this very procedure this weekend to make a 40m inverted V dipole. Worked great!

    73, KF5UPL

  2. CQ
    Using your instructions I am in the process of making 4-12 depending on my initiative :+)I have a few different versions in mind
    different sizes due to lack of material at Home Depot.
    Great post ...Thank You

  3. Hi, nice blog I am radioamater since 1986
    My callsign is 9A7BBW, name Mike QTH Varazdin, CROATIA JN JN86FH

  4. Hi
    this is really very helpful article. I go through this site really very nice information.thank for sharing such a nice information

  5. My son and I made this about two months ago and used it for Boy Scouts Jamboree on the Air. We decided to make it on a whim one afternoon. It was very easy to make. The hardest part was finding the SO-239 chassis mount connector. Luckily, we found one at our local Radio Shack...although the kid behind the counter had now idea what I was looking for ("Is that for the new iPhone 6?"). It's very portable and easy to set up. I'm thinking of getting a portable HF rig and taking it backpacking with our scout troop.

  6. The most important missing instructions are on insulating the coax connector. Wrap the whole thing in duct seal? SO-239 and PL-259 are not waterproof.

  7. I think this is one of the simplest center insulators that you can make, that will stand up to the test of time. I do have one comment, I would be concerned about water infiltration leaking in from the center :I: hook. So, why not completely fill the nipple cap with a silicone sealant sealant just before the final gluing of the two parts.

  8. Just made one of these. Very easy and interesting project for about $10 worth of materials. I am going to make a few more. 73, Dave, KD2INZ

  9. Nice and strong connector, with strain relief as well. And in most cases, especially portable, a balun is not necessary. 73 de vk2dmh

  10. 江浩情緒不穩定

  11. This is the best instruction I could find. Thank you!