How to Make a VHF Radio Antenna?

Also called COLINEAL or “La antenna del RC N,” it was at the Radio Club Ñuñoa where we met her for the first time in the 80s.

Light, medium size, easy to build, and to depend on what materials you will use, its cost is negligible for the performance it provides.

Materials

Vertical section

• 1.5 meters Aluminum 7/8 (seven-eighths of an inch)
• 80 centimeters Aluminum 3/4 (three-quarters of an inch)
• 1 meter of P VC (blue) 20 Millimeters
• Enamelled copper wire 1.6 millimeters in diameter, or otherwise 1.5 mm electric sheathed cable.
• Good quality black isolate.
• 1 1 inch clamp.

Ground plans

• 2 meters Aluminum 1/4 or 2 meters of galvanized wire (not very thin)
• Eight screws (roscalata) 6 * 8 (ideally made of stainless steel)

The antenna has its optimum performance at the proper height (over 6 meters) and at least one lambda away from any metallic element, construction, or another antenna. So we must have enough space and height for us to enjoy your best performance.

We cut the aluminum

Aluminum 7/8:

Cut 1: 52 cm

Cut 2: 30 cm (one of the ends should cut with a saw, in this piece of aluminum)

Balance: 68 cm that will be used to support the antenna and affirm the ground planes.

Aluminum 1/4:

Cut four elements of equal 50 centimeters each.

PVC:

Cut an element of 60 centimeters.

The remaining 40 centimeters will be used to connect the irradiator to the ground plane.

Coil Construction

• Since we want to make a 5/8 wave focus on 1/4, we must build a coil as a solution for the effects of phase compensation, and in this way, the antenna works as a single whole.
• We must then build the coil taking the piece of 60 centimeters of PVC, the wire, and the insulating blanket.
• We wrapped around the PVC. The wire building 34 turns on 50 centimeters of PVC so that it is 5 centimeters free of the coil for each end of the PVC. That is, each turn must be sufficiently spaced and evenly within 50 cm, which we will fix to the PVC with the insulator Hsinchu, carefully covering the whole coil.
• At each end, we must leave enough wire to fix it to aluminum with a roscalata that will also set the coil to aluminum.

Irradiating termination

• We must install the pieces of aluminum one at each end of the PVC, up the part of 30 centimeters, and down the 52 centimeters.
• In the upper part, we will make two cuts along with the piece of aluminum of approximately 20 cm. Long each one where we will put the clamp that will fit the piece of 7/8 to the part of 3/4 and will keep it firm. It is in this section that we will move to adjust the ROE to its best value.
• Finally, in the lower section of the irradiator, we will introduce the piece of 20 Cm PVC that was leftover when cutting the part of the coil. One end to the irradiator and the other to the section of aluminum of 68 cm. The separation between both pieces of aluminum should be 5 millimeters.
• To affirm both pieces with PVC, it is made with two perfectly aligned escalates, one under the other and not more than 15 millimeters from the edge of the aluminum and not less than 10 millimeters.

Ground plans

• The four pieces of aluminum of 1/4 of an inch cut in 4 of 50 centimeters each, or galvanized wire we must install them joined to the PVC of 68 cm inferior, doing across, one in each side and 45 degrees concerning the aluminum inferior 68 cm
• Some modify this 45-degree opening and leave the ground planes at 90 degrees. This is a mistake, since the best impedance of the antenna, that is, the one that comes closest to 50 Ohms is at 45 degrees.
• The installation of the coaxial cable, where the mesh should go directly to one of the escalates that affirms the ground plane immediately below the roscalata that connects the coaxial life.

Adjustment of the antenna

• The antenna is designed to cover a frequency range between 136 and 160 MHz. Optimally 5 Mhz. under 146.0 Mhz. And 5 Mhz. over 146.0 MHz.
• To make it enter immediately in resonance, it will suffice to lengthen or shorten the upper section (a piece of aluminum 80 cm 3/4), using the clamp that will attach this element to the part of 7/8.
• The improvements that can provide this scheme we leave it to the Radio Amateur, without altering the measures (lengths) and separations, only their creativity will make this antenna their trophy.
• The measurements (diameter) in the aluminum and PVC allow each end ideally between one another, if you want to change the diameters, keep this in mind.

As a final recommendation, I recommend using three essential things for this band.

1. An excellent coaxial 50 ohms, and when I speak of an excellent coaxial, I speak of a good one, minimum one RG-214. From this up. The RG-58 or RG-8 is a toy.
2. Seal with silicone (black), the coaxial connection points to the antenna, both in the irradiator and in the ground plane. It is also advisable to use a SO-239 or similar device arranged in a small aluminum “L” plate to connect or disconnect the coaxial cable more efficiently and prevent its handling from cutting it.

3. Eye with the aluminum we buy, anodized aluminum does not work, since it has a layer that protects it, this same layer isolates it and does not conduct electricity, so we would have to sand in each contact.