Ham Radio General Class Test 2025 – 400 Free Practice Questions to Pass the Exam

Question: 1 / 545

How much must the power output of a transmitter be raised to change the S-meter reading on a distant receiver from S8 to S9?

Approximately 1.5 times

Approximately 2 times

Approximately 4 times

To understand why raising the power output to change the S-meter reading from S8 to S9 requires approximately four times the power, it’s important to consider how S-meter readings correlate with signal strength and power levels.

Signal strength indicated on an S-meter generally follows a logarithmic scale, which means that each S-unit is a marker of a significant increase in signal strength. Specifically, an increase of 1 S-unit corresponds to a change of about 6 dB. Therefore, moving from S8 to S9 represents an increase of 6 dB.

Since decibels represent a ratio of power levels, an increase of 6 dB equates to a power increase of a factor of 4. This is because a ratio of power levels can be calculated using the formula for decibels:

\[ \text{dB} = 10 \times \log_{10}\left(\frac{P2}{P1}\right) \]

By rearranging this for a 6dB increase, we find:

\[ 6 = 10 \times \log_{10}\left(\frac{P2}{P1}\right) \]

\[ \log_{10}\left(\frac{P2}{P

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