KB9VBR Antennas

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Build a Dipole Antenna Center Insulator

Posted: 29 Sep 2020 02:06 PM PDT
https://www.jpole-antenna.com/2020/0...nter-insulator



One of the most common and ubiquitous antennas for amateur radio is the
simple dipole antenna. And for good reason‚ dipole antennas are easy to
build and are proven performers.










The ARRL antenna book says this about dipole antennas: The dipole is a
fundamental form of antenna in its most common form it is approximately
one half wave length long at the frequency of use. The name comes from di-
meaning two and -pole meaning part. That relates to the opposite voltages
applied to each half of the antenna so that it has two electrical halves.




Dipoles can be used on just about any amateur radio band‚ but they are most
common on the HF bands- that is on frequencies 30 Mhz and below. Wire
dipoles are easy to construct as you only need a few parts- mostly just an
appropriate length of wire‚ some insulators for the ends and a center
connector. Most of these parts can be purchased from a variety of amateur
radio suppliers both online or at a storefront.




I’m planning to build a linked dipole antenna but I didn’t have a suitable
center connector so the first thing I did was search online. After seeing
prices ranging from 25 $45‚ I decided that I could do better myself; so I
built this dipole antenna center connector for about $12 out of parts
commonly available in your home improvement store. Of course you will need
an SO-239 bulkhead connector. Now of course if you are like me‚ you can
scavenge up most of the parts that were left over from previous projects. I
did have some bulkhead connectors that I picked up from a hamfest years
ago- but since hamfests are few and far between right now‚ you can also
purchase them online.




So in this video I’m going to take you through the steps of building your
own dipole antenna center connector. Once you have all the parts and tools
collected‚ you should be able to put this together in about 30 minutes.








For parts you’ll need:




1 ¾ x ¾ x 1 inch PVC Tee connector
2 ¾ inch PVC plugs
1 1 inch PVC plug
3 3/16 x 1 ½ inch eye bolts
3 Number 10 washers
3 10 x 24 nylon lock nuts
SO-239 bulkhead connector
Rosin core solder and flux




You’ll also need a couple lengths of 14 gauge insulated stranded wire and
some PVC adhesive. I’ll put a full list of the parts necessary in the video
description below.




As for tools‚ you’ll need:
Wire cutter and stripper
Power drill
532 inch drill bit
58 inch spade bit
Vice grips or other locking wrench
Needle Nose Pliers
Small file
High power soldering gun or iron




You will need to solder the 14 gauge wires to the bulkhead connector- a 30
watt pencil tip iron will probably not generate enough heat to do this so I
recommend either a 100 watt soldering gun or a butane iron with a wide tip.




Starting out‚ you will need to drill a few holes into the caps and the tee
connector. Into the two ¾ inch plugs drill a 532 inch hole in the center.
You will then move the nut that came with the eye hook all the way to the
end of the thread and then thread the eye hook through the hole. It will be
a tight fit so work it in. Do this with both ¾ inch plugs.








With the tee connector you will need to drill three 5/32 inch holes. One on
the top of the connector and two under side in the elbow portion of the
Tee. I drilled these bottom holes at an angle as this is where your wire
from the connector will come out. Thread the third eye hook on the top of
the tee just like you did with the plugs.




Moving on to the 1 inch plug. You will need to drill a â…� inch hole into
this plug. I used a spade bit to do that‚ but first drill a pilot hole so
you know you will be centered on the plug. Safety first- PVC is a soft
material so take it easy drilling the hole with the spade bit. I used my
vise grips to securely hold the plug while drilling. Test the bulkhead
connector to make sure it fits. If it doesn’t you can sand out the hole a
bit to make it bigger.




Now we move on to the final assembly. On the back side of the eye bolts‚
place a washer and a locking nut. Tighten the nut with the needle nose
pliers.




Next cut two lengths of 14 gauge wire. Don’t worry about making them too
long- you can trim them later. Make each length about 18 inches long. Next
tie a knot into the wire at about the 4 inch mark. This will prevent the
wire from being pulled out after the connector is fully assembled. Next‚ go
up through the 1 inch hole on the tee and thread the wire through the
drilled hole.




Now you are ready to solder the wires to the connector. First strip about ¼
inch of insulation off the wires and tin them with solder. Next Use the
small file to rough up the chrome finish on the SO-239. Then solder one of
the wires to the center connector. Now to make the process a little easier‚
I’ll dab a bit of flux on the bulkhead connector and place a small pad of
solder. Once that solder has adhered to the connector you can go ahead and
solder the second wire.








Once that is complete‚ let things cool a bit as the connector will be hot.
Then you can push the bulkhead connector through the hole add the lock
washer and jamb nut and tighten things down. If everything looks good- use
the PVC adhesive to seal it up and make your handiwork permanent.




Now a couple of things to note. First off the plugs will not go in all the
way- there will be a slight gap. This is due to the wire and the knot
inside the Tee. The second thing is that there is a slight gap there the
wires exit the tee. You can dab a bit of silicone in there if you want to
make them water tight.




Third and most importantly‚ this is just a center connector- it is not a
1:1 balun. One to one baluns are good for eliminating common mode current
but aren’t a necessary feature of a dipole antenna. You can use a dipole
antenna without a 1:1 balun and it will work just fine. But if common mode
currents are a concern to you‚ you can add some ferrite beads to your
feedline or make a choke out of a few loops of coax.








Like I mentioned earlier in the video‚ this center connector will be part
of a linked dipole antenna project I’m working on. You’ll see that antenna
in a future video.




So there you go. Do you have any questions or comments on the dipole
antenna center connector project? Please leave them in the comments below,
I’d love to hear what I missed so please share your advice too.

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Antennas.