The winning article for the January 2019 QST Cover Plaque award is “The 2-Meter Slot-Cube Antenna” by John Portune, W6NBC.The QST Cover Plaque Award — given to the author or authors of the most popular article in each issue — is determined by a vote of ARRL members on the QST Cover Plaque Poll web page.Cast a ballot for your favorite article in the February issue today. The antenna works well but is difficult to rotate. The photograph below shows the antenna installed at my QTH. The top spreader is 50 feet above ground. The bottom about 20 feet above ground level. HF Skeleton slot. The drawing above shows the dimensions of my Skeleton Slot. It can be easily rotated. It is bi-directional. This two-element Cubical Quad antenna is designed for use on either the 10-meter ham band or the 11-meter Citizen's Band. When all was said and done, my SWR readings were 1.3 to 1.7 on the 10-meter band.

Build a 2 Meter, 5/4 Wave Antenna

By Mike Martell N1HFX

Many RASON members truly enjoyed last month's collinear antenna. This month I decided to build a 2 meter 5/4 wave antenna. This antenna is unique in that it is enclosed entirely in 3/4' PVC which makes the design a little more complicated. The primary problem is that PVC tubing has a significant velocity factor which causes RF to slow down. This means that an antenna encased in PVC will normally need to have it's physical length reduced by about 19%. To further complicate the design, a 5/4 wave antenna's impedance has a highly inductive component which must be tuned out to get a good match. Fortunately, the design in Figure 1 solves all of these problems.

This antenna is made with the following components:

About 2 feet of outdoor type 300 ohm TV twin lead (Used for matching system.)
About 5 feet of #18 stranded insulated wire (Used for radiating element.)
About 5 feet of RG58/U coax
One PL259 Connector
One PL259 female to female coupler
About 8 feet of 3/4' PVC tubing. (normally sold in 10 foot lengths)
Two 3/4' PVC end caps
About 8 feet of 1/4' hardwood dowel (normally sold in 4 or 5 foot lengths)
About 25 small tie wraps
Miscellaneous PVC cement, solder, small piece of tubing, etc.

The twin lead was originally cut for 20 inches with 4 7/8 inches cut back on the braid or ground side. The #18 insulated wire was cut to exactly 57 3/4 inches. The overall length of the antenna assembly is 77 3/4 inches. This indicates a velocity factor of about .81 compared to a normal 5/4 wave 146 Mhz antenna. See calculation below:

Antenna

234 * 5 / 146 X .81 = 6.49 feet or about 77.88 inches

Now that we have all our parts, lets begin assembly by cutting back the insulation of the coax and the TV twin lead. We will need to cut back the coax to expose the center conductor as well as part of the braid. It is a good idea to lightly thin the braid with solder to prevent any strands from shorting out to the center conductor. Solder the center conductor to one end of the twin lead and solder the braid to the other end off the twin lead as in Figure 1. Notice the braid of the coax is soldered to the shorter part of the twin lead which is left open. This serves as our matching system which adds capacitance to our antenna to offset the inductive component of the antenna. Trim the twin lead to 20 inches and solder about 60 inches of #18 stranded wire to the twin lead as in Figure 1. The insulation should not be removed except as necessary for soldering.

2 Meter Slot Cube Antenna

Prepare the 1/4' hardwood dowel by joining two 4 or 5 foot lengths together. The ends can be joined by crimping a 1 inch length of 5/16' aluminum tubing or using a good quality wood glue. Now attach the coax, twin lead and wire assembly to the 1/4' dowel using tie wraps about every 3 inches. Pull the twin lead and wire to keep it as straight as possible. Before attaching the PL259 connector to the coax, drill a hole in one of the PVC end caps and slide it over the coax to prepare for permanent mounting in the PVC. Now attach the PL259 connector as well as any other connectors needed to check SWR. Cut back the open end of the twin lead to about 16 inches as in Figure 1.

Now we are ready for final tuning. Slide the antenna, dowel assembly inside the 3/4' PVC first. All SWR readings must be taken with the antenna, dowel assembly inside the PVC tubing or the antenna will appear electrically shorter than necessary. Check SWR on both the top and bottom edge of the band. If the SWR is higher at 147.995 Mhz than at 144.005 Mhz then the antenna is too long and should be shortened. Cut off no more than a 1/4' at a time of the #18 wire. Also, trim the open end of the twin lead by no more than 1/8' at a time to further lower SWR. Remember the twin lead is simply a matching system which changes impedance and has no real effect on the electrical lengh of the antenna. The final lenghs of the #18 wire and twin lead should very closely resemble those listed in Figure 1. The prototype antenna achieved SWR readings of less then 1.2 to 1 across the entire 2 meter band. Remember to keep the antenna away from metal objects when checking SWR.

After the antenna is properly tuned, trim the antenna dowel assembly to about 7 feet. Leave a few inches of coax attached to the bottom of the dowel so that the mast will be away from the twin lead portion of the antenna when mounted. Trim the PVC tubing to about 7' 2' and cement the top end cap. Double check SWR before cementing the bottom end cap. After SWR has been doubled checked, slide the antenna, dowel assembly into the PVC and cement the bottom end cap. If desired, styrofoam spacers may be used to get a very snug fit. Waterproof the bottom end cap where the coax leaves the antenna. When completed, the antenna should resemble Figure 2.

When mounting the antenna, use a PL259 female to female coupler. Do not use RG58/U for the entire feed line because it is too lossy. Use good quality RG8/U or similar coax for the feedline. Of course, do not forget to waterproof the female to female coupler. Mount to any mast using standard TV antenna clamps at the bottom of the antenna and keep it high and away from other metal objects for best performance and lowest SWR.

Although not actually measured, this antenna should give at least 6 dB gain if mounted high enough. Remember, the small diameter of the radiating element has no effect on the radiation resistance. The only real benefit with using a large diameter radiating element is durability and slightly improved bandwidth. This antenna should give many years of reliable performance for a fraction of the cost of a commercial antenna.

DE N1HFX

2 Meter Slot Cube Antenna

Meter

I decided it was time to set up a 2 Meter base station. Being the crafty maker type, I wanted to build my own antenna. I settled on a 2 meter vertical dipole. I proceeded to make a very heavy dipole from copper pipe, akin to the type used for J-poles. It was incredibly heavy and very quickly became a sagging and corroded eyesore on the corner of my house.

I decided to go back to the drawing board and starting from scratch, designed an entirely new, much lighter, 2 meter vertical dipole. This antenna offers an air choke to keep stray RF from wondering back into the shack, since I’m pushing 65 watts. Also with vertical dipoles you want the feedline extending perpendicular to the antenna for at least 1/4 wavelength for good SWR.

Everything to make this antenna should be available at your local hardware store with the exception of the feedline and any RF connectors. You may have a lot of it laying around the shack already. I encourage you to experiment and make this design your own. Use what you already have and play around with modifications to what I’ve done.

Parts List

  • 3/4” PVC pipe (I grabbed one 5 foot length)
  • 1” PVC pipe (I grabbed one 5 foot length)
  • 1 3/4” PVC Slip 90
  • 1 3/4” PVC Slip Tee
  • 1 3/4” x 1” PVC Slip Tee
  • 2 3/4” PVC slip plugs
  • 2 steel rods roughly 1/8” and about 19″-20” long (I cut longer pieces down)
  • 2 Copper Terminal Lugs (I used Thomas & Betts pn: BTC0614-B2)
  • 2 small ring terminals (anything 12 to 16 AWG should work)
  • 4 or 5 wire ties
  • Electrical Tape
  • About 3 foot of your favorite flavor of feedline(I used RG58)
  • RF connector of your choice (I used a BNC for RG58)
  • Nuts and bolts that fit your lugs and ring terminals

Tools Needed

  • Drill with bits the size of feedline and bolts
  • Dremel tool with grinding wheel or a file
  • Tools required to install RF connector
  • Hot Glue Gun
  • SWR meter or antenna analyzer
  • Solder and soldering station(optional)
  • Something to cut PVC pipe(I use a metal pipe cutting tool)

The Build

Start by aligning the terminal lugs to the outer edges of the Tee as shown in the picture, drilling holes through the pipe and bolting them into place loosely(we’ll take them back off later) The terminal lug has sort of a lip on it and I go this as close to the edge of the pipe as possible so when tight, it would help hole the lug upright. Also at this point, loosen the terminal lugs and flip the heads around 180. This allows the steel rods to go all the way through the lug instead of bottoming out and places them toward the outside of the pipe tee instead of toward the inside.

Next we cut a length of 3/4” pipe a touch longer than 1/4 wavelength, about 20 inches long and lightly push it into the remaining hole on that same tee. Then, coming back an extra half inch or so and drill a hole the size of your chosen feedline into the pipe. Test wrap about 5-7 wraps of your feedline around the pipe starting at the hole, then mark for a second hole along the same line as the first and drill one there. This will be for your air choke. Once wrapped, we can wrap the choke tightly with electrical tape to help hold it in place. Depending on how weatherproof you want this, you may opt to cover it in some type of liquid electrical tape as well.

Before you get to wrapping the coil, however, we need to push a few inches of feedline through the hole closest to the end of the pipe, and prepare the shield and center conductor for ring terminals. Leave enough insulation off to reach both bolts on the tee. Crimp a ring terminal on the center conductor and one on the shielding. At this point I soldered the ring terminals in place for added strength, and covered them in heat shrink tubing with only the ring exposed. This is all optional.

Take the nuts off of the bolts on the terminal lugs, push on the ring terminals, and replace the nuts. Tighten them down really good until the nuts start to pull into the PVC. You may opt for washers on the outside of the tee. Now push the ¼ wavelength piece of pipe into the tee very tight, and pull the excess feedling back through the hole you drilled so no excess is in the end of the antenna. Wrap 5-7 wraps and push the feedline in the second hole and out the long end of the pipe. You’ll need about 8-15 inches or so of feedling sticking out the far end. Of the pipe, for your RF Connection. Also place the 3/4″ X 1″ Tee on the other end of the pipe. Throughout the rest of this process make sure the center conductor is attatched to the element sticking up and the sheilding to the counterpoise sticking down.

Next take the two 3/4” caps and notch them out as shown and push them on over the terminal lugs. I used a dremel tool with grinding wheel for this but you may have a better option available. Cut the steel rods down to ¼ wavelength for 2 meters. This runs between 19 and 20 inches. Because we are using an inch or so of the feedline as part of the radiating element(inside the tee) I simply cut mine down to 19 inches. Do this with a dremel tool, or a file, or other tool of your choice. (Don’t ruin your wire-cutters or strippers by using them! The steel is a lot harder than it looks!) Run a steel rod into each of the terminal lugs and out the other side a half inch or so then tighten the lugs.

Cut 1-2 inches of 3/4” pipe and put it on the opposite end of the tee with a 3/4” 90 off of it and push your feedline through all this as you do it. Next cut a section of 1” pipe long enough to mount the antenna where you want and push it into the bottom of the 3/4″ X 1″ tee. Cut one last 3/4” piece of pipe about a foot or so long and hold on to it for use later.

Make sure all your pipe is together tight and at this point if you want to use pipe glue, do it. I opted just to use hot glue at all the seams once my antenna was completed.

2 Meter Slot Cube Antenna Arrl

Cut your feedline down so only 3 or 4 inches are coming out of the antenna and put on your RF connector of choice find a temporary stand for your antenna.(I used the base and stand of an old house fan). Using and SWR meter or an antenna analyzer, test for a good SWR on the two meter band.(I tried to center around 146MHz)

How to make a 2-meter slot-cube antenna

2 Meter Slot Cube Antenna

Adjust the two steel rods in or out to change SWR until you have a good match. Once matched, tighten down the terminal lug screws, and run a wire tie around the side of the tee and the stub of the steel rod sticking out the bottom of the lug. This just removes possible stress on the lug itself if it gets pushed toward the feedline end of the antenna. Seal all seams with hot glue, then mount in your permanent location. Run your extra piece of 3/4” pipe on the outgoing feedline and after connecting to your antenna, push it onto the remaining side of the 90, just using friction to hold it in place. This is the last little bit of quick and dirty waterproofing. Now use a few wire ties to tie the incoming feedling to the main mast.

How To Make A 2-meter Slot-cube Antenna

Hook to your base station(or HT) and enjoy! Some of the hardware may rust over time, so when the antenna gets in bad shape I’ll simple replace the bad hardware with new. It’s cheap. Otherwise you could use something to seal the exposed metal parts. I installed this in an old dish mount on the corner of my house at about 15 feet and it bought me about 25 miles extra distance over my rubber duck antennas.