Each month features an updated reprise of a Tech Tip from ten years ago because many past Tech Tips are well worth review. Also, some will benefit from updating. Enjoy the thirty-fourth monthly Tech Tip reprise.
The dictionary defines “propagation” as the spreading of a transmission. A wireless mic transmitter emits a Radio Frequency (RF) wave and this wave spreads away from the transmitter, i.e., RF wave propagation.
Water waves propagate. Drop a pebble in a quiet pond, and the waves propagate outward from where the pebble broke the water surface. Sound waves also propagate in a manner similar to pond waves.
Wave propagation
Be it RF waves, water waves, or sound waves, longer waves travel [propagate] longer distances. Longer wavelengths also pass around large obstacles. A tsunami can create wavelength hundreds of miles in length. The tsunami wave can propagate for thousands of miles and pass around objects of massive size. At an outdoor concert, low frequency sound (bass guitar) can be heard at a much greater distance than high frequency sound (cymbals) because low frequencies have long wavelengths that travel farther.
How long are the RF wavelengths emitted by our wireless mic transmitters?
- VHF wireless, ULXD-V50 series: 200 MHz = 59.0 inches/150 cm
- UHF wireless, ULXD-G50 series: 500 MHz = 23.6 inches/60 cm
- UHF wireless, ULXD-J50A series: 600 MHz = 19.6 inches/50 cm
- UHF wireless, ULXD-X52 series: 900 MHz = 13.1 inches/33 cm
- UHF wireless, MXW series: 1.9 GHz = 6.2 inches/16 cm
- UHF wireless, GLXD+ series: 2.4 GHz = 4.9 inches/12 cm
- SHF wireless, GLXD+ series: 5.8 GHz = 1.9 inches/5 cm
A simple ratio exists. When the frequency is multiplied by two, the wavelength is divided by two. If the frequency doubles, from 200 MHz to 400 MHz as an example, the wavelength is halved, from 59.0 inches to 28.5 inches. Thus, the wavelength at 800 MHz is 14.2 inches; at 1.6 GHz it is 7.1 inches.
Consider a quarter-wave antenna and a half-wave antenna. At 600 MHz, the wavelength is 19.6 inches according to the list above. One quarter of 19.6 inches is 4.9 inches. Thus, a 600 MHz quarter-wave antenna will be between 4 and 6 inches in length. A 600 MHz half-wave antenna will typically be between 8 and 12 inches in length.
Looking at the wavelengths above, one will understand how the human body is massive enough to obstruct a frequency of 2.4 GHz (4.9 inches) but not a frequency at 200 MHz (59.0 inches).
As the frequency gets higher, the wavelength gets shorter. As the wavelength gets shorter, the wave propagation acts more like visible light, i.e., directional. When operating in higher frequency ranges, maintain line-of-sight between the transmitter and the receiver antennas for reliable operation.
Related information: Online RF Wavelength Calculator
Selection and Operation of Wireless Microphones – Tim Vear, author
Arcana – mysterious or specialized knowledge
