Project 17: Quarter Wave Monopole Antenna.

2022-10-10

Objective:

To build a quarter wave ground plane monopole antenna tuned to 465 MHz.

Radiating length is calculated by 0.25 * Wavelength * VF. Measured from the base insulator.

Assume VF is 0.95

Radial length is 1.1 * Radiating length and the are four radials extending at 40deg angle from base, Measured from center of antenna.

To build one antenna cost $5.37, with no labor included.

Materials:

1. 12 AWG Solid Copper wire.

2. 1 piece - N-Type Female Jack 4 Hole PCB Panel Mount Solder RF Connector Adapter.

3. 4 pieces - Terminal Block Set, Wire Connector Block, 10A 380V

4. 4 pieces - M2.5 Flat Washers

5. Solder Iron.

6. Solder, flux, and other cleaning materials

7. Misc. tools

Build Procedure and Testing:

1. Cut out the length of the 1X radiating and 4X radial lengths. Straighten pieces, use a drill to twist wire, forward and reverse, to straighten if necessary. Gather the rest of the materials.

2. Screw together terminals to the Type N-Female connector.

3. Bend radial legs to 40deg angle.

4. Screw the copper pieces to the N-connector. Make sure radial legs are spaced 90deg circumferentially.

5. Solder the radiating length to the N-connector.

6. Check radiating element that there are no shorts to ground and there is good conductivity to end connector.

7. Test SWR of the antenna (require a separate connector to connect antenna to radio). For this project used a SureCom SW-33 meter, and it measured 1.01 for the homemade antenna compared to 1.68 for the rubber ducky that came with portable radio.

Conclusion

The home made Quarter Wave Monopole Antenna was a success. It is an indoor use only because construction would not be able to handle an outdoor environment.