Q: Why do you need an antenna for DTV even if you didn't need one for analog?
A: Short answer: the DTV signal is carrying more information than analog, so the reception needs to be clearer.
Here are some details.
Possible Problems with Old Antennas:
1. Outside antennas are exposed to the elements, and need to be replaced every so often.
2. Old antennas might have old wires. The old flat brown wires on antennas will not work, and only RG6 cables will work well. (Other round cables don’t work well, either, just RG6).
3. Your old antenna might be UHF only – and the new digital stations might be VHF. Or, the new digital stations might be temporarily UHF and will change back to VHF after the analog channels are shut down. Explain.
4. Digital “Cliff Effect.” See below.
5. If you're at the outer reaches of the broadcast signal, you may need to install an amplifier. It's best to install the amplifier at the antenna, not at the television.
6. Indoor antennas don’t work very well for digital. See below.
What is the digital Cliff Effect?
The digital "Cliff Effect" causes digital signals to be either clear or 'not clear.' Since it's carrying more information, if the tuner is out of range, it can't see all of the information it needs to create a television picture. That makes it stutter and pause while the information is gathered. If the signal is too weak, there's no 'snow' - the digital television will just show 'no signal.'
There was a larger 'grey area' with partial signals in analog. With analog, we're so used to 'ghosting' and semi-clear signals that we don't even notice the problem sometimes.
Video explanation of the Cliff Effect.
Why don’t indoor antennas work well?
The digital signal is also very much 'line-of-sight.' That means it can be confounded by objects such as trees, towers, buildings, and even fog. So raising it to your roof or attic might help you get better reception.
Demonstration of rabbit ears indoors vs. other choices.