For those of you who are new to over-the-air terrestrial television, note the following warning when re-scanning.

The Virtual channel may actually broadcast on a different Radio Frequency (RF) channel than its virtual channel, such as   broadcasting on RF channel .

When you re-scan your TV or converter box, you end up erasing the previous found links between the virtual channel and RF channel.  For example, if you scan your TV and successfully receive channel 39, but can't get channel , you would move your antenna in another direction then have to re-scan to pick up .

However, you might discover you lost channel 39; your TV has reset channel 39 to its default RF  when you rescanned the second time.  Your TV is now looking for channel 39 on RF  not on RF .

Some TVs have a manual RF channel edit process which is preferable in situations like this.  Otherwise it is a tedious back and forth task.