i have been told time of day matters for hf propagation. for example, 80m works best at night. but if i qso with someone on the other side of the world, it's daytime. do they just need more power? can i expect to tx better at night and rx better during daytime (or vice versa)?
Feel free to read up on the following articles:
With HF ( High Frequency ) the signals are refracted by the "Ionospheric modes (skywave)" back to earth and reflected by the earth itself.
The ionosphere is impacted by the sun spots from the sun.
I've checked this forum and these articles may interest you: