Question 1A6

Frequency tolerance, expressed in parts-per-million (ppm), defines the maximum allowable deviation from a designated frequency. To determine if a measured frequency is within tolerance, you calculate the absolute deviation in Hertz. For 156.875 MHz: The allowed deviation is $156,875,000 \text{ Hz} \times (5 / 1,000,000) = 784.375 \text{ Hz}$. This means the frequency must be between $156,875,000 \text{ Hz} - 784.375 \text{ Hz}$ and $156,875,000 \text{ Hz} + 784.375 \text{ Hz}$, or $156,874.216 \text{ kHz}$ and $156,875.784 \text{ kHz}$. For 157.200 MHz: The allowed deviation is $157,200,000 \text{ Hz} \times (5 / 1,000,000) = 786 \text{ Hz}$. The frequency must be between $157,200,000 \text{ Hz} - 786 \text{ Hz}$ and $157,200,000 \text{ Hz} + 786 \text{ Hz}$, or $157,199.214 \text{ kHz}$ and $157,200.786 \text{ kHz}$. Examining the options: * **A, C, and D** contain at least one frequency that falls outside these calculated legal ranges. * **B) 156,875.774 kHz and 157.199.321 kHz:** Both frequencies are within their respective calculated tolerance ranges ($156,874.216 \text{ kHz}$ to $156,875.784 \text{ kHz}$ and $157,199.214 \text{ kHz}$ to $157,200.786 \text{ kHz}$). Therefore, only option B represents frequencies that are within the 5 ppm legal tolerance, crucial for preventing interference and complying with FCC regulations.