41. Geometrical acoustics is the approximate theory, which is valid in the limiting case of very small acoustic wavelengths, or very high frequencies . 42. For example, when rats are threatened, they emit very high frequency ( 20, 000 to 30, 000 cycles per second ) screams. 43. :One way to think about it is that your infrared remote control is a wireless transmitter, just a very high frequency one. 44. However, very low frequency waves would be impossible to detect and there is no credible source for detectable waves of very high frequency . 45. Vacuum tube devices dominate high power ( hundreds of kilowatts ) at very high frequency ( hundreds or thousands of megahertz ) applications. 46. Additionally, at very high frequencies ( microwave ), RF power meters still use thermal techniques to convert the RF energy to a voltage. 47. The inversion is capable of allowing very high frequency ( VHF ) and UHF signal propagation well beyond the normal radio horizon distance. 48. First, he thought in terms of generating light waves with their very high frequencies rather than radio waves with their much lower frequencies. 49. SELCAL operates on the high frequency ( HF ) or very high frequency ( VHF ) radio frequency bands used for aircraft communications. 50. All the bands mentioned in this article are in the very high frequency ( VHF ) range, which extends from 30 to 300 MHz.
