Option C: Shortwave Listening

Req 8c3 — Compare Day & Night Logs

8c3.

Compare your daytime and nighttime logs; note the frequencies on which your selected stations were loudest during each session. Explain differences in the signal strength from one period to the next.

How to Compare Your Logs

Create a side-by-side comparison of your shortwave listening sessions:

What to Look For

Which frequencies had the strongest signals during the day? Higher shortwave frequencies (15–21 MHz) tend to be more active during daylight because the ionosphere is more strongly ionized by the sun, supporting refraction at higher frequencies.
Which frequencies had the strongest signals at night? Lower frequencies (5–9 MHz) tend to dominate at night. The D layer of the ionosphere, which absorbs lower-frequency signals during the day, disappears after sunset, allowing those signals to reach the higher F layer and propagate long distances.
Did any stations appear in one session but not another? A station that was clearly audible at 10 PM may be completely absent at 2 PM — or vice versa. This is normal and expected.
Did signal strength fluctuate during a session? Fading (QSB in ham terminology) is common on shortwave. The signal may cycle between strong and weak over periods of seconds to minutes as the ionosphere shifts.

Why Signals Change

The ionosphere is not static — it responds to:

Sunlight: More ionization during the day, less at night
Solar activity: Sunspots, solar flares, and coronal mass ejections can dramatically improve or destroy HF propagation
Season: Summer and winter ionospheres behave differently
Frequency: Each frequency has a “best” time of day for long-distance propagation