28 MHz is high enough that the ionosphere can only just bend it back down. It takes a hard-ionised F2 layer to do it, and that takes solar flux. Below about 90 the signal punches straight through into space and is simply gone.
28 MHz is high enough that the ionosphere can only just bend it back down. It takes a hard-ionised F2 layer to do it, and that takes solar flux. Below about 90 the signal punches straight through into space and is simply gone.
For example, at a flux of 115 the band opens, but thinly, and only while the sun is high. It shuts almost the moment the sun sets.
The exception is sporadic E in June and July — dense patches form in a lower layer and 10 meters goes wild for an hour with no warning, flux or no flux.
| FREQUENCY (MHz) | MODE | LICENSE CLASS |
|---|---|---|
| 28.000–28.300 | CW / RTTY / data | Technician and above, General, Advanced, Extra |
| 28.300–28.500 | Voice — Novice & Technician | Technician and above, General, Advanced, Extra |
| 28.500–29.000 | Voice | General, Advanced, Extra |
| 29.000–29.520 | Voice / AM | General, Advanced, Extra |
| 29.520–29.600 | Satellite downlink | General, Advanced, Extra |
| 29.600–29.700 | FM | General, Advanced, Extra |