2 Meter Slot Cube Antenna Arrl

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HF Skeleton Slot - An antenna system with a difference.

For many years at this QTH I have tried different wire antennas. Not being interested in rotary beams of the usual type, I have always use fixed wire antennas.

Over the years I came to the conclusion that for my particular purposes I needed something with gain that would work in more than one direction.

Having tried vertical beams and phased verticals all hanging from a nylon line, I decided to use the same nylon line to hold up a Lazy H antenna.

Doublet – Multi-band antenna that is not resonant on a particular band. 88 ft and 44 ft are popular lengths. Requires antenna tuner. (3/2 λ) doublet with 31 (1/4 λ) ft of ladder line, then fed with coax. Designed as a 20m antenna. Multi-band with antenna tuner. Extended Double Zepp – Longer than a dipole. In some ways the slot provides more flexibility because it enables the length of the loop to be altered to tune the 2 metre quad to exact electrical resonance. Cross members of the 2 metre cubical quad antenna. The next stage is to join and glue two cross members to make the characteristic ‘X’ of the 2 metre cubical quad antenna. The winning article for the December 2019 QST Cover Plaque award is “Slot Cube Antenna for 6 Meters” 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. This is my first home brew “DIY” antenna for use on local 2 meter repeaters and simplex frequencies. The photo to the right is an example of how the antenna may be supported with minimal holes or damage to the wall. It’s modeled after the basic delta loop design and is fed with a 1/4 wavelength of 75 ohm coax (RG-59U).

The Lazy H works very well of course, Bi-directional, low angle and gain, BUT its a bit too big to rotate to fill in the directions 90° from its broadside line of fire and I don't have the room to put up a second Lazy H.

It was while playing around with this antenna using the MMANA-GAL modeling program that I tried bending the ends of the top dipole down and the ends of the bottom dipole up, still keeping the open wire phasing line between the two dipoles and fed in the center. I eventually ended up with the ends of the dipoles joined together and the horizontal top and bottom parts of the dipoles very much shortened and tried feeding at the junction of the dipole ends, getting rid of the phasing line between the two dipoles.

This arrangement now reminded me of the VHF skeleton slot antenna that I had seen in an old RSGB handbook, but a search on the Internet turned up nothing for an HF version.

More adjustments in the MMANA-GAL program showed that the antenna should perform well on all bands from 30 meters to 10 meters.

To get the low angle take off, the bottom of the antenna needs to be about 15 feet (4.5M) off the ground. It will still work if the bottom is lower but with a higher angle of take off.

I purchased a Pump up mast 50 feet (15m) and a small cord operated rotator. The top horizontal spreader is fixed to this rotator and the whole antenna hangs down from there.

The MMANA-GAL program can be found here.

Below are the dimensions I used for the Lazy-H antenna.

The plot below shows the gain and angle of elevation of the Lazy-H, as computed with MMANA-GAL. 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. It has high gain, low angle of elevation, and can work on all bands from 10 to 30 MHz.

Below are the plots of the Slot for the bands 20m, 17m, 15m and 10m.

Below is shown a 'BowTie' version.

It has slightly higher gain and lower angle of elevation.

The corresponding plots are shown below.

This picture shows the bowtie version at GW3RQT(SK)'s

The small marine ply support for the spreaders can be seen in the center.

The short horizontal bamboo in the center is to support the dog bone insulator and the open line feeder together with the vertical wires coming from the four corners.

Alan GW3RQT(SK) uses the same antenna but with smaller dimensions as his mast is only 30 feet high.

It is designed for 15m but works well on all bands from 10 to 20m.The plots are shown below.

He uses spreaders for the diagonals mounted on a rectangular piece of marine ply with U bolts.

The center is then raised to the top of the mast which gives a height of 15 feet from the bottom of the antenna above ground.

Constructional details

The antenna is very easy and inexpensive to make. For the sake of clarity, the constructional details are on another page.

Conclusions

The skeleton slot antenna is very cheap and simple to make - mine consists of three bamboo spreaders and copper wire!! It is fed in the middle of the center wire with open wire line which is taken to an antenna tuning unit in the shack.

Results have been excellent and quite a lot of DX has been worked on digital modes using 50 watts even through the odd pile up .. With such a broad horizontal pattern I only need to turn the antenna 90° to get pretty well full coverage of the world . For example with the antenna in a NE/SW direction, stations from K4 down to LU and JA down to VK6.

Have fun 73 Don G3VCG

My e-mail address is here

Build a 2 Meter, 5/4 Wave Antenna

By Mike Martell N1HFX

2 Meter Slot Cube Antenna Arrl

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:

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.

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.

2 Meter Slot Cube Antenna Arrl Antenna

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.

2 Meter Slot Cube Antenna Arrl Amateur Radio

DE N1HFX

2 Meter Slot Cube Antenna Arrl Ham Radio