Stacked Dipole for 11M

Stacked Perpendicular Dipoles for 11M

I'm fairly new to radio but I am already hooked.  One of the aspects I really enjoy is building my own antennas.  I had already built a 1/4 wave ground plane vertical that worked quite well, I was able to get contacts out nearly 1000mi when conditions were good.  However, I wanted something with a bit more punch so I decided to build a dipole which would double my gain.

The only problem with a dipole is that it is directional so I would always have a deaf spot of about 30 degrees on each side of the dipole.  I wanted to eliminate that as much as possible so I began to try to work out different ideas.  At first I wanted to run two dipoles that were phased together but I wasn't sure how well it would work and the modeling software really only showed good signal propagation when the two dipoles where half a wavelength apart.  This meant that they needed to be 5.5 m or 18 ft apart.  This would make the antenna quite large and I had a max height of 65 ft as I would be hanging this from a tree outside of my shack.  That wasn't going to work.

Plan B: I dropped the top dipole down to just a couple of feet above the bottom and modeled that in software running only one dipole at a time.  This gave me about 8db gain and solved my 'deaf' problem.  Here is the antenna in the modeling software.

Here is the SWR prediction and gain for several frequencies (26.155 was a typo) with the bottom of the antenna at 18m/60ft 

This is the far field plot of one of the dipoles, you can see at the height of 18m/60ft we get several lobes and a very low take-off angle

2D version of the far field, here I have the bottom most lobe marked and you can see it has 8db of gain @ 8 degrees

Now that my concept was proved I just needed to build it.  The next question was what to build it with.  I figured I could use PVC and pipe to build a structure that would hold up and perform well.  I had initially decided on copper pipe but I found that 1/2 copper pipe was a bit too flimsy for this application and 3/4 pipe was going to be too expensive.  I settled on 1/2 EMT electrical tubing.  This also saved me about $32 just on the elements alone as the 3/4 copper pipe is about $12 and the EMT is about $4.  For the structure of the antenna I decided to use 1" PVC pipe.  In fact, the only elements with metal in them are the small ring I use to connect the antenna to the rope, the elements and the coax.  Everything else is PVC and rigging.

The Build

 Here are all of the parts that I used for this build.

• 4 - 1/2" EMT electrical conduit @ 10 feet
• 4 - 1/2" EMT compression fittings
• 3 - 1" PVC pipe sections @ 2 feet
• 2 - 1" PVC cross connectors
• 2 - 1 1/4" PVC cross connectors
• 4 - 1" PVC plug with 1/2" threaded connection
• 4 - Metal screws
• 1 - Stainless Steel quick link (3/16 I believe)
• Paracord 550lb test, 160lb working load
• 2 - 1" PVC threaded connector (not pictured)
• PVC cement (not pictured)

Additional Misc items

• zip ties
• heat shrink wrap
• hot glue

First step is to build the main body of the antenna.  We will use one 2' section of the PVC pipe and both 1" PVC cross connectors.  We will glue these perpendicular to each other.  This is rather important to the build so I recommend dry fitting them, marking the alignment and then gluing.

Next, we will glue the 1" plug with 1/2" thread into each of the horizontal openings in the cross connectors.

Now we need to drill holes in the top/bottom of the 1 1/4" cross connectors.  Originally I had intended to fit the 1" pipe in snug and glue it in place but found my hole to be a little too large.  Ultimately I ended up using the threaded 1" connector (which I happened to have on hand) to glue into the hole instead.  I think this was the better option.

1 1/4" cross connector with 1" threaded fitting glued in.

This would not work well except that the force we are going to be putting on this connection is going to be in favor of the glue and not working against it.  With that in mind, we move on to the next step.  We will glue the 2' sections of PVC into our fittings that we glued into our 1 1/4" cross. 

For the base we will then take that section and glue it in place opposite of our crosses that the antenna elements will screw into.  This was my attempt at picturing what I am saying.  It will become more apparent later in the build.

Now we can add the top section to match the element fittings. They will be inline with each other to allow the support rigging.  This is what your finished body should look like.

Hopefully here you can see that the top of the body is inline with the element sections and the bottom is offset.

Now we will add the compression fittings to the EMT pipe.  First, prep the end of the pipe with some sand paper to allow for a good electrical connection.  Next, put on the fitting discarding the lock ring as it won't be needed. This is a two wrench job, you'll need something with teeth to grab the fitting and a wrench to get a good tight on the locking nut. **Do this for all four elements**

Now we will cut the EMT pipe to the appropriate length.  My modeling software told me that my element needed to be 2.675m long which is about 105.5 inches so I measured from the end of the fitting to the pipe 106.5 inches to allow myself a bit of room to adjust.  Once they are cut, you just need to screw them into the pvc connector.  Get some help with this part as the antenna quickly becomes a bit unruly.  In fact, so much so that I forgot to take pictures of this part of the build so I'll use some later photos to show what I did.  Work on one set of elements at a time.  Have someone hold one side while you screw in the other.

Next take some of your rope and tie a clove hitch (or your favorite constrictor knot) near the end,I did about 1ft, of the pipe, run the rope through the top cross and tie the other end on the opposite element. I also tied an overhand knot with the slack end of the clove hitch to the main rope to prevent it from working loose.  This will allow the weight of the pipe to be carried by the structure and not put strain on the compression fittings and pvc connectors.  The type of knot is important because you want it to lock onto the pipe and not slide as this will be under constant tension.  Adjust the knots until the two elements are hanging at 90 degrees to the body.  Here is a photo that shows the elements rigged up.

The next step is to add the rigging for hanging the antenna.  I used two separate runs of rope through the bottom cross, up the sides of the body and through the 'elbows' of the top cross.  Where they cross over at the top, I added my quick link.  The ropes are tied together using fisherman's knots on each end so that when they slide together they put tension on each other. Take time to make these as close to the same length as is possible so that you have the best resutls.

Bottom of the antenna body with rigging ran through bottom cross connector.  All of the weight is carried from the bottom.

Top of the rigging showing how the lines pass through the elbow of the top cross and connect with the quick link.

At this point I hung the antenna low to the ground to make it easier to work on.  With the rigging set up this way, all of the weight is carried from the bottom of the antenna.  It is being lifted up into the tree, not pulled.

In the conduit, drill one hole (appropriate size for your screws) in each element.

I am using RG6Q coax for this build.  I was able to get a 500' spool of coax at Home depot for $60.  It's hard to find good numbers on this stuff, but best I can figure, it's somewhere between RG8X and RG213.  I prepped the coax by removing about 5" of sheath from the outside and then began to work back the braid. RG6Q is the quad shield and it has two braids, I used both for the best possible connection.  I recommend gently pushing the braid toward the sheath so that it bunches up then taking a small tool to carefully pull individual sections of the braid out.  I did not do this on the first connection and it took me quite a while longer to deal with the rats nest I created.

At the end of the center conductor I bent it over to allow me to attach it with the screw to the element.  On the braid side, I used a crimp fitting with a appropriately sized hole for my screw.  I attached the coax with zip ties from the top down to help prevent water intrusion, I also used heat shrink wrap to further seal the coax.

Now I zip tied a small loop above the connections and ran the wire down the side into an air choke.  The choke is wrapped around a 4" PVC pipe that I happened to have from a previous build (this can be anything about 4" round which is why it is not included in the parts list.  You could even do this by hand if you want.  The coax is wrapped 6 times and the whole assembly ends up to be about 2.5" wide.

The top of this loop was pulled toward the middle and tied in place before raising the antenna.

Both antennas connected, chokes installed and coax tied to mast with zip ties.

The final touch to prevent water intrusion was to hot glue over top of the connections to the elements.

Here is the finished antenna, ready to be raised.

The antenna is 'done' and could be raised at this point, but I like mine to be a bit more hidden up in the tree so I always cover my antennas with a bit of rust-oleum camouflage paint.

Here is what it looks like after:

And here it is up in the tree:

Additional guy lines are used to prevent/discourage twisting so I have a better idea of which way the antenna is facing.

Now for the testing.  Once I had all of my coax connections made, I moved on to SWR testing.  Here are the results:

• CH1 26.965 - 1.3:1
• CH40 27.405 - 1:1
• CH16 27.155 - 1.2:1

For some anecdotal, non-scientific results I can tell you that last night May 19, 2020 I got reports from Ontario Canada (about 650mi) that I was 7x9 loud and clear.  I'd say she's working.  I use an antenna switch to switch between each of the dipoles.