Don't fall for this digital TV antenna myth

If those claims instantly make you skeptical, your instincts are right. The reality is that TV signals have physical limits, and while the marketers might try, no antenna can overcome the curvature of the Earth. Before you buy an antenna with the biggest mileage rating, it's worth taking a look at what really determines how far you'll be able to get a usable signal.

Hsyn20/Shutterstock If 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.

Let's assume you're using an indoor antenna. One For All, a brand selling TV antennas globally, claims that its indoor antennas have a 25 to 60 mile range , but its "usual rule of thumb" is to only use one when you're 15 miles away from your nearest transmitter. It also recommends that houses surrounded by obstacles, like trees or buildings, situated more than three miles away from the transmitter will need to use an amplified TV antenna to boost the signal a little further.

Outdoor antennas will let you pick up signals from further away. Placing the antenna outside means you're reducing the last obstacle, your house walls, and installing it at a high level improves line of sight between it and the transmitter. Antennas Direct suggests that 70 miles is the effective limit for line-of-sight for UHF signals , with low UHF and high VHF signals able to pass a little further, for instance.