N2CX 40-30-20m Portable Tri-Band Vertical Antenna
Joe Everheart N2CX can probably best described as a “QRP Guru”. Joe’s tips regularly appear in issues of “QRP Quarterly” published by the QRP-ARCI. He and George N2APB were the brain trust behind Atlanticon and are still the brain trust behind the NJQRP. They are both QRP geniuses.
Joe’s antennas were of course, of his own design. The QRP Guys persuaded to coax some of Joe’s antenna secrets out of him and they are offering his Tri-band (covering 40, 30 and 20 Meters) NPOTA antenna as their newest kit. You can get the details here:
With permission from Joe Everhart, (N2CX), we have adapted his 40-30-20m portable vertical antenna design using switched toroids for the base loading inductance into a lightweight antenna for an easy outdoor setup. His full article can be read on the July 2017 issue of The QRP Quarterly. With this kit, user supplied wire, and an easy obtained vertical support, you can produce a switched tri-band vertical antenna virtually anywhere.
Joe has logged thousands of NPOTA contacts in the last couple of years using his design. We have incorporated his toroids and added a switched design into a small package that will easily attach to the base of a telescoping fiberglass fishing rod used as the vertical wire support. Low cost, ~$10 USD telescoping fishing rods, that collapse to 26″ are easily available through eBay, and with user supplied 20-26awg wire will make a tri-band vertical antenna. In absence of the the vertical support, a wire could be held vertically with lightweight cord in a tree or similar structure. Four 10′ long ground plane radials are attached to the base at the ground wingnut. The ~16ft. long radiating element can be wound on the pcb for easy storage.
The device is rated for 10W, has all captive stainless steel hardware for the antenna, counterpoise connections, and a female BNC for connection to your radio. With 17′ of 24awg stranded wire it weighs less than 2.5 oz.(70gm). On a difficulty scale of 1 to 5, 5 being the most difficult, this is rated at 2.
1 – QRPGuys TBV pcb 1 – L1,2 T68-2 toroid core (red)
1 – 72” of 26awg magnet wire
1 – BNC female horizontal connector
2 – S1,2, SPDT slide switch
2 – 8-32 x 3/4”L SS Phillips pan head screw 4 – 8-32 SS nut
2 – #8 internal tooth SS lock washer 2 – 8-32 SS wing nut 4 – nylon tie wrap
Refer to the graphic below and the PCB silk screening for the placement of the components.
With a file or emery paper, smooth the sharp edges of the two notches on each side of the pcb, otherwise if you attach the device to your vertical pole using rubber bands, the sharp edges can cut the rubber bands.
Install S1,2, soldering all 5 pins on each.
Install the horizontal BNC connector
Install the hardware posts for the “Antenna” and “Gnd.” as shown in the figure below. The post screw should be flush with the outside of the securing nut. Install the “Antenna” hardware with the wingnut on the front side. Install the “Gnd.” hardware with the wingnut on the backside.
Next to install is L1 that must be wound as shown below in order for the wires to line up with the holes. Use 30” of wire and wind 24 turns. Remember every time the wire passes through the center of the core counts as one turn. Tin the wires before installing onto the pcb. Install the wound toroid flush with the top of the board. When the wires are bent down, they will align with the pcb holes.
Next to install is L2 that must be wound as shown below in order for the wires to line up with the holes. Use 36” of wire and wind 38 turns. Remember every time the wire passes through the center of the core counts as one turn. Tin the wires before installing onto the pcb. Install the wound toroid flush with the top of the board. When the wires are bent down, they will align with the pcb holes.
Using the antenna:
The QRPGuys Tri-Band Antenna covers 40-30-20m. The builder supplies the wire for the driven element and ground plane wires. You can use 20awg to 26awg depending what you have available for the wire. We have designed the device to mount on the base of a fiberglass telescopic 7.2m (5.4m/17.7” useable) fishing pole, available on eBay. However any non-metallic support may be used. The device is very lightweight and can be attached to the 01” base diameter of the fiberglass pole easily with rubber bands that align with the notches in the pcb. There is a BNC female connector for the input from your radio. Use four 10’ counterpoise/ground wires attached to the ground wingnut that can just be laid on the ground radially from the base.
Setting up the antenna for the first time
Use a 17’ long piece of wire for the vertical element. Deploy the four 10’ radials, set the switches for 20m and adjust the length of the driven element for 20m, folding back the wire for lowest SWR, ~2:1. When finished fold back the driven element on itself, and secure it. Our experience is that after tuning it for 20m, the antenna will be ~2:1 on the other two bands with the proper switch settings. You may need to squeeze or expand the turns on L1 for 30m and L2 for 40m to obtain these results. Do not change the length of the radiating element. If you want the SWR to be less or broader coverage, just use a tuner for the whole band.
We have found the inductance values and setup description the best compromise for all three bands. We encourage experimentation and if you use only one or two of the bands you may want to try different inductances and driven element lengths.
You can keep the vertical antenna wire attached to the J3 wingnut and wind around the pcb for compact storage.
In eBay, search for “telescoping fishing pole”. You will need a plain one, without any eyes, and an expanded length of at least 17’. The best useable one is advertised as 7.2m long (useable length is 5.4m/17.7’). Collapsed length is only about 65cm/25.6”. They are referred to as fiberglass or carbon fiber construction. Typically ~$10 USD delivered.