Building your own antenna can be both fun and educational, not to mention there is something about being able to say "I built it myself!" that makes it worth the time and effort. However, it would be far to hard for us to explain everything there is to know about building an antennas, so instead we would like to refer you to The ARRL Antenna Book. This is a book filled to the brim with everything there is to know about designing, constructing, and tweaking antennas. If you are going to build an antenna, you need to look no further.
Besides checking out The ARRL Antenna Book, here are a few of our own tips on building antennas:
One of the most useful things to know when building an antenna is the wavelength for the frequency in question. Below is a chart of the wavelengths for a half-wave dipole antenna:
The equation used to find the above lengths is:
length (in feet) = 468 / f (MHz)
Please keep in mind that the chart above gives only the approximate length of wire to use when building a HF dipole antenna. The equation will not be as accurate for VHF and UHF antenna lengths.
Below is a chart of the wavelengths for a quarter-wave vertical antenna:
Remember that the values given above for the UHF and VHF bands are for comparison purposes only. These lengths will serve as a good starting point for building antennas for 2 meters, 1.25 meters, 70 centimeters, or 23 centimeters.
After cutting the wire to the length given by the equations you will need to adjust the tuning of your antenna for the best operation. For this you will want to put the antenna in its final location and check the SWR at various frequencies across the band you intend to use. It helps to plot the SWR values on a graph with the frequency and draw a smooth curve between the points. This graph will indicate if your antenna is too long or too short. If you have a higher SWR at the low frequency end of the band then your antenna is too short. On the other hand, if your SWR is higher at the high frequency end of the band, the antenna is too long. When you have your antenna properly tuned the lowest SWR value should be around the frequency on which you plan to operate most.
These are just a few tips we thought you might find useful. If you have any questions concerning building your own antenna, remember to always ask a neighboring ham. Good luck and have fun!