Work through these in order. The first fixes cost nothing, and rescan after each change so the TV picks up what you gained.
Is your antenna high enough and pointed the right way?
Height matters most. Antennas Direct puts it plainly: "Higher is always better" (Antennas Direct). Indoors, try a higher spot on a wall or window that faces the towers. Outdoors, a few extra feet above the roofline can clear nearby obstacles.
Aim at the towers. Your city page shows the compass direction and distance to every station. Channel Master notes that small moves can make a big difference, so turn the antenna a little at a time and rescan (Channel Master).
The FCC's reception maps color-code each station's predicted signal at your address as strong, moderate, weak or no signal, and show the direction to its tower (FCC map guide).
What is blocking the signal?
Hills, buildings and trees between you and the towers weaken the signal, and metal blocks it most (Antennas Direct). Trees are worth a second look if reception got worse over time. Channel Master points out that trees can grow into the signal path (Channel Master).
Could something in your home be causing interference?
Some LED lights give off interference that can knock out channels (Channel Master). Test it: turn off the lights near the antenna or TV and see if the channel comes back.
Cell towers are another source: their LTE signals can overload a TV tuner. An LTE filter blocks them. Channel Master says to put it as close to the antenna as possible, before any amplifier or splitter, and notes that all signal levels drop slightly when you add one (Channel Master).
Does your antenna receive VHF?
Most stations broadcast on UHF, but some use VHF. Many indoor and flat antennas are built mainly for UHF. If you're missing only certain channels, check their band on your city page. Antennas Direct says it's necessary to use an antenna optimized for both UHF and VHF to receive those stations (Antennas Direct).
Are your cables and connectors in good shape?
Check that every connector is screwed on snugly, and look for corrosion on outdoor fittings (Antennas Direct). Take out any splitters you don't need, because each one weakens the signal. Our guide to several TVs has the numbers.
When does an amplifier help, and when does it hurt?
An amplifier makes up for loss in long cable runs and splitters. It can't create signal the antenna doesn't receive. Channel Master says a preamplifier is useful "when the antenna receives usable signals but additional gain is needed," and that it "should not be viewed as a way to repair a poor signal" (Channel Master).
- Preamplifier: mounted at or very close to the antenna. Best for distant stations and long cable runs.
- Distribution amplifier: farther downstream, indoors. Best for feeding several TVs through splitters.
Too much gain is a real problem. Channel Master warns that unnecessary amplification can overload the preamplifier or TV tuner and make reception worse. If your stations are close and strong, Antennas Direct suggests an attenuator to bring the signal down instead (Antennas Direct). Your city page says whether an amplifier is likely to help where you live.