Subelement L: L – Installation, Maintenance & Repair— Topic 78: Measurement Procedures
Question 3-78L6
Element 3 (GROL)What is the maximum FM deviation for voice operation of a normal wideband channel on VHF and UHF?
Explanation
For normal wideband FM (WBFM) voice operation on VHF and UHF, the standard maximum frequency deviation is **5.0 kHz**.
This deviation level provides excellent audio fidelity for voice communications while efficiently utilizing the assigned channel bandwidth, typically 20 kHz or 25 kHz. This 5.0 kHz deviation, combined with a typical maximum voice audio frequency of 3 kHz, results in a transmitted bandwidth of approximately 16 kHz according to Carson's Rule (2 * (deviation + highest audio frequency)), fitting well within common channel spacing.
* **A) 2.5 kHz** is the maximum deviation for *narrowband FM* (NBFM), which uses less spectrum and is often found on channels with 12.5 kHz spacing.
* **C) 7.5 kHz** and **D) 10 kHz** would be considered excessive for normal voice, leading to wider bandwidths that could cause interference to adjacent channels and are not standard practice for typical amateur wideband FM voice.
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