Although these frequencies are not normally thought to be bands where propagation occurs there are times when it signals on VHF and UHF travel well beyond their expected distance. These conditions generally occur erratically and are not as predictable as HF conditions. Some of the conditions that can affect VHF and UHF are:
- Tropo - This condition refers to tropospheric propagation which is primarily affected by weather systems. Look for significant weather changes such as a cold front moving in or a major storm system. Also early evening as the earth cools and early mornings as the earth warms can cause these conditions.
- Sporadic E - occurs when small patches of the ionosphere are ionized . Sporadic E occurs during June-July and early August and again in December and January. as the name suggests this condition is sporadic and you have to be very patient to benefit from it.
- Aurora - The northern lights (aurora borealis) occurs in the northern parts of Canada and can also be seen from northern U.S. states. The "lights" are caused by a solar storm and can have an effect on radio propagation. If can affect VHF and UHF as well as HF propagation. To use the aurora you may need to point your antenna north to work a station to the south as signals bounce back from the aurora.