Subelement A: VHF-DSC Equipment & Operation— Topic :
Question 1A3
Element 9 (GMDSS Maintainer)What is the assigned channel spacing for VHF channels?
Explanation
The standard channel spacing assigned for amateur radio VHF FM voice operations, particularly in the popular 2-meter band, is 25 kHz. This spacing allows for efficient utilization of the spectrum while providing adequate separation between channels to prevent adjacent channel interference.
Amateur radio generally uses narrow-band FM (NBFM) for voice transmissions, which typically occupy a bandwidth of about 15-20 kHz. A 25 kHz channel spacing accommodates this signal bandwidth, plus a small guard band, without wasting excessive spectrum. Options A and B (10 kHz and 15 kHz) would be too narrow, leading to significant interference between channels. Option D (50 kHz) would be unnecessarily wide for NBFM, resulting in inefficient use of the limited amateur radio spectrum. This 25 kHz standard is widely adopted in repeater coordination plans and general operating practices.
Related Questions
1A1 What are the correct VHF Channels and Frequencies for Calling/Distress, DSC and bridge-to-bridge operations?1A2 What is the frequency separation between Transmit and Receive frequencies on a duplex channel?1A4 What is the allowed frequency tolerance for the DSC carrier frequencies?1A5 Using a frequency counter with an accuracy of 2 ppm — which of the following are within legal tolerance for the frequencies of 156.800 MHz and 156.525 MHz?1A6 Using a frequency counter with an accuracy of 5 ppm — which of the following are within legal tolerance for the frequencies of 156.875 MHz and 157.200?