Have noticed that many of the selected channels come up with the "Notice: No Signal" prompt, does this means that this/those channels will never be viewable, because the receiver is not able to lock them in, or are these channels signals are not actually strong enough for the receiver to make them viewable. If giving enough time for the receiver to try to lock in the channel`s signal, will they ever come in.

What is a true sign or prompt that will indicate that this or any channel will not be received and viewed.

Thanks.