If one antenna is good, aren’t two better? That’s the idea behind stacking antennas. Put one antenna next to or on top of another and you’ll get better reception. It’s actually the basis behind antennas like our Xtreme Signal HDB8X, which is really just four of our HDB2X antennas put together in a way that makes sense.
Stacking works, but you need to be aware of some simple guidelines.
You don’t get double the gain.
It would be great if you could take two antennas with a gain of 3dB and combine them into one antenna with a gain of 6dB. In a perfect world, you could. But there are a lot of factors that go into stacking antennas that introduce some loss of signal. There are additional cables, combiners, and some small degree of interference between the antennas. You should figure on losing up to 4dB when combining antennas, so two 4dB antennas stacked together may actually not have any better performance than a single 4dB antenna. If you’re combining, it’s best to combine antennas that already have fairly high gain so that the loss you get while combining doesn’t completely suck up any improvements you’ll get.
You need to mind a minimum distance.
Because of the way signals are actually received, you need to make sure the two antennas are a certain distance apart from each other. The guideline I was always taught was, at least the wavelength of the channel you want to get. In most cases, the longest wavelength you’ll try to receive is on VHF channel 7, which is a little more than six feet. So with a UHF/VHF antenna, you must have at least six feet of separation. With a UHF-only antenna, that number drops to a little over two feet, and remember we’re talking about the distance between the receiving elements (often the bow-tie or X-shaped parts of the antenna) not the reflectors (often the tallest, widest part of the antenna.) So if you’re putting together a stacked array of UHF antennas, they can be quite close and still work.
You need to make sure your cables are the same length and same construction.
This is an important part of the plan. If your cables going into the combiner are not the same length, then the signals from those antennas won’t reach the combiner at the same time. The difference may be tiny, but it may be enough to create phasing problems. When the two signals get to the combiner at two different times (here’s a simple illustration)
they don’t result in one stronger signal but instead a weaker, less useful signal. In extreme cases if the signals are exactly 180 degrees out of phase they actually cancel each other out and you get nothing at all.
A lot of people talk about keeping the cables the same length but don’t talk about making sure that you use two basically identical cables. If the cable types are different, or if the connectors are different, you can have the same phasing problems.
Make sure you’re using the right kind of combiner.
A lot of people will choose the wrong combiner and end up with one that combines ONLY UHF on one side and ONLY VHF on the other, which isn’t going to help you when combining antennas. A combiner like that is just going to give you the same signal strength as a single antenna.
I like this Winegard combiner which is designed specifically for the purpose but I’ll be honest with you, in most cases a very simple splitter, turned upside down, is all you will need. The cheaper the splitter, the more likely it is to be a good combiner, because it won’t have fancy features designed to prevent its use as a combiner. Personally I’d start with the less expensive one and move up to the more expensive one if you’re having problems.
But at the end of the day, should you combine antennas? Sometimes two smaller antennas can work better than one large one if you are in an area where the signal is bouncing off a lot of buildings. However, most people are going to want to stack antennas to try to get reception past 100 miles, and in cases like that they usually don’t work. The signal is so weak by the time it gets to you, and there is so much noise, that it would take a miracle to get those signals to you, unless you are willing to put the antennas as high as possible, to eliminate any obstructions like trees and buildings.