Ham Radio General Class Practice Test

What is the most common frequency shift for RTTY emissions in the amateur HF bands?

1. 85 Hz

2. 170 Hz

3. 425 Hz

4. 850 Hz

The correct answer is: 170 Hz

The most common frequency shift for RTTY (Radio Teletype) emissions in the amateur HF bands is 170 Hz. This frequency shift is standard for most RTTY operations because it effectively allows for the reliable transmission of data while minimizing interference between signals. RTTY uses frequency modulation (FSK), sending information through shifts in frequency. The 170 Hz shift strikes a balance between sufficient separation to prevent overlap of signals (which causes interference) and maintaining a compact bandwidth that is efficient for transmission over HF. In contrast, other shifts like 85 Hz are less common, as they may not provide enough separation between signals, leading to potential cross-talk. Higher shifts, such as 425 Hz or 850 Hz, are used in some other types of digital modes or in specialized applications but are not typically standard for RTTY in the amateur bands, as they could require more bandwidth and be less efficient for standard transmissions. Thus, the choice of 170 Hz reflects a widely accepted standard in amateur radio practice for RTTY communication.