A random wire antenna [1] is comprised of a long wire above ground that is used to transmit and receive signals. This is a quick way to add an antenna to radio equipment.
However, it is not an optimal antenna design and so when it is used with a transmitter or receiver, the radio range performance can vary greatly.
To calculate the physical length of a wire antenna
Enter
- High (H) and Low (L) Frequencies – this represents the frequency range of the antenna
- Wavelength
To design an antenna at a single frequency, enter the same value for both upper and lower.
Example Antennas
The picture below shows a wire antenna soldered on to a PCB to provide 2.4 GHz Wi-Fi connectivity. In this particular case it is a quarter wavelength wire with a length of approximately 3 cm.
Use the above calculator to confirm this by entering 2400 MHz (Lower) and 2500 MHz (Upper) and quarter wavelength.
A random wire antenna does not follow any specific pattern or design. Due to the random nature of its length and placement, these antennas can have a wide range of impedance values. However, they tend to have a low feed point impedance, which makes them easier to match to the transmitter or receiver. This makes them a popular choice for many amateur radio operators.
Example Calculation
A wire antenna that is used for both Wi-Fi bands (2400 MHz and 5800 MHz) has the following lengths depending
| Wire Antenna Type | Physical Length (cm) |
|---|---|
| λ | 7.3 |
| λ/2 | 3.7 |
| λ/4 | 1.8 |
A commercial low-cost wire antenna shown below has a length of 8.5 cm including the external enclosure. While the structure itself is that of a monopole antenna, the dimensions are closer to that of a 7.3 cm wire antenna from the table above (dimensions are a little larger on account of the plastic enclosure).
General Precautions
In general we do not recommend the use of a wire antenna for a Power Amplifier or transmitting radio equipment without a good matching network design. A poor match at the output of the transmitter can result in reflections (use the SWR to Reflected Power calculator to find the percentage) and damage the radio electronics.
Related Calculators
- Dipole Antenna Length
- Whip Antenna Calculator
- Monopole Antenna Calculator
- Frequency to Wavelength
- Wavelength to Frequency
References
[1] Wire antenna on Wikipedia