Match your vertical antenna to your radio to achieve resonance and highest radiated signal efficiency.
A properly designed and installed ham radio antenna matches the radio's transmitted frequency. When a good match is achieved, the antenna is said to be in resonance with the radio transmitter. Vertical antennas are compact, efficient, broad-banded and easy to analyze with simple tools and methods. Check your vertical amateur radio antenna for resonance to maximize your RF signal output.
Instructions
Check a Vertical Ham Radio Antenna for Resonance
1. Measure the physical height of your vertical antenna and apply the formula, Height (feet) = 234 / Frequency (MHz) to see if the height of your vertical antenna matches the frequency upon which you intend to transmit. For example, if you intend to transmit on 14.0 MHz [234/14.0 = 16.7 feet], you will need a 1/4 wavelength vertical antenna approximately 16.7 feet high.
2. Use an antenna analyzer to check your installed antenna for resonance. Connect the antenna analyzer directly to the coaxial cable transmission line of your antenna. Set the analyzer's band switch to the band of your intended transmitted frequency. Dial the analyzer's frequency adjustment knob until you read a 1:1 standing wave ratio (SWR). The frequency readout displays the resonant frequency of your antenna.
3. Adjust your antenna to achieve resonance on your intended operating frequency. If the analyzed resonant frequency is too high, lengthen your antenna in increments until it reaches a 1:1 SWR on your intended operating frequency. If the analyzed resonant frequency of the antenna is too low, shorten the antenna in increments until you reach 1:1 SWR your intended operating frequency.
4. Check your antenna for resonance using an inline SWR meter. Connect the output of the SWR meter to the coaxial cable line to the antenna. Use a short coax to connect your transmitter to the input of the SWR meter. Place the FWD/REF switch in FWD (forward power) position. Key the transmitter and adjust the set knob to the SET position on the meter.
5. Place the FWD/ REF switch in the REF (reflected power) position and read the meter. The lower this reading is, the closer your antenna is to resonance. A perfect 1:1 match is ideal and is 100 percent resonant. Anything below 1.5:1 is acceptable and close to resonance. Anything over 2:1 is less efficient. Transmitting at high SWRs of greater than 2:1 is not recommended and can damage your transmitter or transceiver. Tune your antenna by adjusting its length until a 1:1 SWR is reached.
6. Use an antenna tuner when your antenna cannot be tuned to resonance or when it is to be used on a variety of other amateur radio wavelength bands. Most antenna tuners have built-in SWR meters with either a pair of crossed needles or a pair of separate meters for forward and reflected power. Use the tuner's SWR meter information to either adjust your antenna as described previously or to match your antenna using the tuner's matching network.
7. Adjust the antenna tuner's inductor switch and variable transmitter and antenna capacitors to achieve a 1:1 SWR on your intended output frequency. Monitor SWR continuously while you operate to maintain the efficiency of your station, to maximize your radiated signal and to protect your equipment from potential damage due to high SWR mismatches.
