Introduction: My Experiment in Building a Vertical Dipole Antenna
This project came about when I decided to pull out an old Corba 148 GTL cb I have had in storage for many years. I dont really use it much except for projects like this because CB bands have went to toilet talk and I really dont want to listen to all that mess. But I'm getting ready (saving up) to get a 10 meter ham radio and will be needing a base antenna for it. But my old CB base antenna I had is long gone and I had always wanted to see how a vertical dipole antenna would work. Since 10 meters and cb (sometimes refered as 11meter) are so close in bandwidth often a cb antenna can be tuned for 10 meter. So I checked out vertical dipoles for cb and just couldn't bring myself to pay that much for a manufactured one. So what to do? Simple answer! - Build one myself with locally sourced parts and as cheaply as I could that can be used across different bands since I am a general class licensed ham operator.
Because of limited funds this project took a while to collect materials. Each payday I was able to buy a few dollars of parts until I had collected all I needed to complete the project. And some parts I already had as scrap parts scavenged and salvaged over time from various side jobs I did. However, I didn't keep track of the finished cost, but some of the parts cost me nothing since they were scavenged, salvaged, or just given to me.
Note: This is my first Instructable. Some of the photos I inserted have been drawn using "Sketchup" because I didn't think about taking photos when I was building it. I get tunnel vision when I do a project. So I made drawings to help illustrate the process. I hope they make sense.
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Step 1: Research, Research and More Research.
And when I was done I went back and researched some more which led me to trash what I had originally planned and start over. I have listed two sites which helped me the most in my research to build this antenna so to give proper credit:
http://188.8.131.52/~goranl/building/aircore_bal... I used the info on his 1:1 Balun design.
http://www.amateurradio.bz/ I used inspiration from his you tube pages on his "Peg Leg CB Radio Base Station Antenna"
Step 2: Gather Materials and Tools
- 1 - 3/8" x 10' hard copper pipe (Cut it in half to make 2 - 5ft radials)
- 1 - 1/2" x 10' hard copper pipe (Cut it in half to make 2 - 5ft radials)
- 2 - 3/8" copper caps
- 2 - 1/2" copper male adapters14 awg solid core, insulated wire
- 1 - 1/2" x 5" peice of PVC pipe
- 2 - 1/2" x 3/4" PVC reducer
- 2 - hose clamps
- 1 - 3/4" x 3/4" x 3/4" metal (NOT PVC) conduit body T with cover and weather seal gasket
- 1 - 3/4" x 4' steel black pipe2 - U Bolts 3/4"wide x 1 1/2" long
- 2 - U Bolts 1 1/2" wide x 2 1/2" long
- 1 - 4" x 8" mild steel plate (Or what ever size you need )
- 50' coax cable RG8X coax cable
- electrical tape
- 1 -PL259 Coax plug connector Or what ever connector your radio needs.
- drill bits
- propane torch
- solder iron
- hack saw
- nut driver
- wire strippers
- emery cloth,wire brush or sand paper
- tape measure
- electrical tape
- coax jumper
- SWR Meter
Step 3: The Radials
Do the following twice to build the 2 separate sides of the dipole.
- Cut 1 inch notches on both sides of the 1/2" copper pipe on one end of each pipe with the hack saw going down the length of the pipe. this creates a compression joint to later put the hose clamps on.
- Prep for Solder = Clean the opposite end of the 1/2" copper pipe with emery cloth and the inside joint of the 1/2" male adapters.
- Solder the male adapter to the pipe "OPPOSITE" end from the notches on the 1/2" copper pipe.
- Take a 3 to 5" piece of copper wire and strip on end and solder it "INSIDE" the end of the male adapter to create an electrical connection point that will later be connected to the balun. Do not get solder onto the threads of the male adapter. (Been there done that and it's a PAIN).
- Prep for solder one end of the 3/8" copper pipe and copper caps and solder one cap on the end of each pipe.
- Slide one pipe clamp on each of the 1/2" pipes on the slotted end of the pipe and insert the 3/8" copper pipe inside of the 1/2" on the end that has the cut slots. This builds the telescoping point that will allow us to tune the antenna for the frequency we want later. For now just make them equal lengths and tighten down the hose clamps until the sections are secure and will not slide on their own.
Step 4: Assemble the T
- Thread on a 1/2" x 3/4" pvc reducer on each of the "COOLED" male adapters and then thread these two sections into the opposite ends of the metal conduit body T. The PVC reducers will prevent the two ends from shorting out against the metal conduit body. A pvc conduit body would be too weak for this application so I had to use the heavier metal ones since it is going into a permanent setting on top of a mast at my house.
- Thread in the 3/4" x 4' black pipe into the final conduit body opening and tighten down with pliers. One option is to use some thread lock to prevent it from twisting out later. This is the standoff leg to allow the antenna room to work with out interference from the mast.
Step 5: Antenna Bracket Plate
Drill 8 holes the to insert the u bolts in the metal plate. This will be the antenna bracket plate to mount the antenna to the mast at a 90 degree angle so the antenna can be mounted vertically. However you can mount it horizontally if you desire. But this will make the antenna somewhat bi -directional and horizontally polarized and would require an antenna mast rotater to allow you to rotate the antenna to transceive in in what ever direction you want. Horizontally it would transceive somewhat equally in 2 directions with little reception or transmision pointed toward the ends of the antenna. So I kept mine vertical to allow it to work omni-directional (Vertically polarized).
Mount the standoff pipe to the plate with the u - bolts. Later mount this plate to the mast with the 2 remaining u bolts.
Step 6: Build the 1:1 Balun
Now build a 1:1 Balun. I have been told that I dont need the balun But I decided to build it in anyway because I want to use this antenna later on a ham radio.
I built the balun using SM2YER design on his website. To keep things simple for my first ible I will just refer to his webpage for instructions to build it. I just made the feedpoint leads to come out the side of the balun instead of inline like he did his. See his website for building the balun. Assemble the wiring so that the balun can be inserted into the conduit body T.
Insulate any exposed electrical connection with tape, or liquid tape, etc... so that it dosent ground out against the conduit body.
Step 7: Final Connections
Insert the coax into the end of the standoff boom next to the mast and fish it to the conduit body where the connections will be made. Install your coax connector (PL259) on the opposite end of the coax.
Seal the end of the standoff boom where the coax comes in to prevent moisture intrusion with tape or caulk or what ever you have.
Make the wire connections and insulate any exposed wire with electrical tape or heat shrink tubing, etc...install the cover plate
Mount the antenna on the mast but make sure you can reach it so that it can be tuned.
Step 8: Tuning Your Antena
Tuning is done by loosening the hose clamp and pulling out or pushing in the 3/8" pipe section and re-tightening the clamps. But both sides of the antenna must be extended to the same length. Use your measuring tape to make sure both sides are the same. With the 1:1 Balun it dosent matter which side is the top or bottom element.
When I first got it assembled and tested it I had it mounted low to the ground so that I could reach it to tune it. My SWR reading was 1.2 on ch 1,1.1 on ch 20, and 1.2 on ch 40. But when I raised it up to full height the readings went up to 1.4 on ch 1, 1.3 on ch 20 and 1.4 on ch 40. I believe that its because is mounted too close close to my open stub J-pole antenna for 2m/70cm. But they are readings I can live with. i may get a longer standoff arm later but for now it works. However, I don't intend on using it for CB for long I am waiting to get a 10 meter HF soon and plan on re-tuning it for that band..