Intercom devices wired with Ethernet cables (CAT5 or CAT6 with RJ45 connectors) solve a lot of communication problems, but there are times when you simply cannot run a cable over a long distance, or through concrete or some other obstruction. Fortunately, there are reasonably priced ways to convert standard Ethernet devices to wireless.

wireless bridgeA “wireless bridge” or “Wi-Fi bridge” does exactly what it sounds like it should do. These devices build a wireless bridge between two remote points. The bridge consists of two devices. One plugs in to your communications equipment at the local location, and the other at the remote location. Using our truck scale application as an example, one device is used in the scale house, while the other is at the truck scale. The antennas on the devices are pointed at each other. The antennas convert wired CAT5 to wireless and then convert it back again to wired on the other side.

There are two types of wireless bridges; point to multi-point or single-point. The multi-point is like a cell phone tower that is broadcasting to many devices. The single point is as it sounds, broadcasting from one antenna to another antenna. However, even though you broadcast to a single antenna, we will show you a way you can still run multiple devices from this antenna. Single point is the easiest to install.

Let’s use an example of a bi-directional scale truck scale, meaning trucks come in and go out on the same scale. So there needs to be an intercom on each side of the scale so they are properly located at the driver’s window. In this case you could use a single-point wireless bridge to get the signal from the scale house to the scale, but then the two intercoms at the scale would require a CAT5 cable as shown in the following diagram.

wireless truck scale intercom
 
In the above diagram, the phones in the scale house plug into a Power over Ethernet (POE) switch that provides the power to the phones. The bridge antenna also plugs into the switch. The intercoms and the antenna on the truck scale plug in to another POE switch on the scale side. The wireless bridge devices are powered by a 24-volt power injector so you will either need to use the injectors that come with the units or use a 24-volt to 48-volt converter to plug directly into the POE switch.

This truck scale system would perform identically as if you had run two separate CAT-5 cables from the POE switch in the scale house over to the intercoms on the truck scale.

We recommend that these wireless bridges have line-of-sight, which means there are no obstructions between the two points. You can do this by putting the bridge devices, or their antennas up high. With line-of-sight you can reach distances of miles with the right bridging device. Some devices can go 10 miles or even more if you put them up high enough to reach over obstructions.

If you have multiple scales and there is no way to run cables between them, then you will need a multipoint wireless bridge. The antenna at the scale house will need to be able to broadcast to multiple points so the placement of your scales will dictate the angle of the wireless beam, and therefore antenna, you use at the scale house. The further apart the scales are the wider the beam needs to be.

Installation
The downside of these wireless bridges is they can be complex to install. Because of that we recommend that you find someone familiar with installation to install them. You can search Google for “wireless bridge installation YourCityName” or “wireless network installation YourCityName” to find qualified people.

Equipment
Most installers will likely have their favorite equipment they like to use, but one example of a low-cost wireless bridge is the Ubiquiti NanobeamM5, which is priced under $200. What equipment you use is not as important as having someone who knows how to install it properly.

Since you may need to place an Ethernet switch outdoors, you will need a weatherproof outdoor enclosure to house it in. You can use this one or something like it: Weatherproof Enclosure

Achieving Line of Sight
True line of site is more than just being able to see the other antenna. For distances over a few hundred feet, antenna placement is extremely important as shown in the illustration below. When an antenna radiates it doesn't just send signals straight point-to-point. Signals radiate out in a cone shape so some signals go up in the air while others bounce off the ground or other obstructions. So parts of the signal take longer to get to the receiving antenna and if they arrive 180 degrees out of phase with the straight-line signal, they can cancel each other out resulting in poor or no audio and video.

To achieve long-range wireless video transmission, optimally you would place the antennas 15-20 feet above any obstructions as shown in the illustration below.
Line of Sight Affects Long Range Video Transmission

Obstructed line of sight for video camera
If you have no obstructions other than the ground then you still want to shoot for getting the antenna as high as possible to achieve maximum distance as shown in the illustration below. Believe it or not, the ground actually counts as an obstacle!
ground plan affects long range video

If you are installing your system in the winter, be sure to factor in any trees between the transmitter and receiver. What works perfectly well in the winter may not work at all in the summer when the trees grow their leaves. The moisture-laden leaves are good at blocking signals.

trees restrict long-range video transmission

Another factor to consider as interference are items that move. In the illustration below, the video is fine as long as the truck is not in the way. The solution is to raise the antenna so you always have line of sight.

Wireless Truck Scale Video System

So, if you simply cannot run CAT5 wire where you need communication, a wireless bridge is an effective and fairly low cost way to convert wired equipment to wireless.

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