GoKawiilIf you head to Amazon and search for digital TV antennas, you'll see results that include indoor antennas with ranges that stretch from hundreds to thousands of miles. The worst offender is one claiming to offer 6,000 miles of range. To put that into context, the distance between London and Los Angeles is roughly 5,454 miles.
No antenna in the world is letting you pick up the BBC in LA. It isn't giving you 1,000, or 500 or even 150. It's not a matter of power, either, as TV transmitters can broadcast a strong enough signal. Instead, to watch over-the-air local TV, what you'll need is a reasonably clear line of sight with the transmitter.
When signals are transmitted from a transmitter, they aren't following the curvature of the earth. Instead, they travel outwards. The Earth is curved, so distant transmitters will eventually disappear below the horizon. Once a transmitter is beyond the horizon, its signal can no longer provide reliable direct reception. The horizon blocks the path. Atmospheric conditions might bounce it a little further, but not by far. You've also got buildings, trees, hills, mountains and more that can degrade the perfect line of sight, reducing the signal distance further.
A digital antenna is just picking up VHF and UHF radio-frequency signals used to transmit encoded digital TV. Digital broadcasting can't eliminate these physical limitations, and there's no transmitter practically high enough to make 6,000 miles, or even 150 miles of range possible, even with an outdoor antenna in the perfect environment.
High-gain antennas are also another marketing claim you'll need to watch out for. Antenna gain describes how well an antenna can focus on a signal in one direction, which is particularly important for outdoor antennas, but it doesn't guarantee better range.