This is our Xtreme Signal HDB91X antenna. It’s designed to pick up UHF signals at astounding distances, and it does. But, if you read the fine print we also tell you that it will pick up VHF signals at fairly close range. Occasionally people show up telling me the site is lying, that this is a UHF-only antenna.
So let me set the record straight.
This antenna does pick up VHF signals at up to 25 miles. Now, I’ll admit it’s not incredibly good at it, and you can use a much smaller antenna to pick up signals from 25 miles away. In fact a coat hanger or even a potato can pick up VHF channels from 25 miles away. So it shouldn’t be a surprise that a TV antenna can do it. In fact almost all TV antennas can bring in VHF signals no matter what they’re designed for. For that matter, most of them can bring in cellular, police band, aircraft, what have you. They just don’t do it very well.
An antenna has to be specially designed to reject other signals. Our Televes antennas reject all but the signals they’re intended to receive so that there’s no interference with other signals as can sometimes happen. But less expensive antennas don’t, and sometimes that’s an advantage.
So here’s why you can do it. An antenna will pick up pretty much all frequencies, but the frequencies that it’s pretty good at will be the ones where the size of the antenna is close to an even fraction of the size of the signal wave. If the wave is 5.5 feet long (which would put on channel 7, by the way) you can best receive it with an antenna 5.5 feet long, or 2.75 feet long, or 1.375 feet long, or so on. Even if the size is off by a little bit, it’s still going to work, which is why you can have one antenna that picks up a lot of frequencies. But let’s say that your average TV antenna is about 14 inches in length, which is about the size of the antenna on the HDB91X. Turns out that’s fairly close to 1/4 the length of channel 7’s wave, so what do you know — that antenna’s going to pick up channel 7 pretty well, more or less by accident.
These “accidents of reception” are so common that you find them in all sorts of antennas, and they can help you get channels you wouldn’t otherwise get. Now, the other side of it is that the UHF antenna is only 1/4 the size of channel 7’s signal, but it’s almost exactly the same size as channel 40’s signal, so it’s going to do about 400% better at picking up channel 40 than channel 7. That’s why we rate our HDB91X so low for VHF reception.
Of course, that same math also applies to other frequencies too, which is why more expensive antennas put in filters to make sure you don’t accidentally get other signals. That makes them more efficient at picking up what they are designed for but eliminates those happy “accidents of reception.”