Radio Mounting in General

The following is an excerpt from a closed thread that I am posting here as well. These guidelines are gathered from several years of troubleshooting and from results during the Einstein Weekend. The reference is for the DAP1522, the current radio. Hope it helps…

While placing the radio deep inside the robot, behind metallic parts, behind the the bumper, on the floor of the chassis pan or behind an arm are all very bad locations, the orientation of the radio (with respect to the field, the Cisco router or other robots) varied the received signal level by less than 10dB. Even if the radio was located low on the robot and on the outside, turning the robot so that the radio was facing away from the Cisco router (with all of the robot structure in the path) only made about a 10 dB difference, far less than I would have thought knowing the interior construction of the radio and placement of the PIFA antennas inside. In fact nearby objects only started to affect signal strength when within 2" of the top or sides of the radio.

So for teams, in general, mount the radio where it is protected from contact with other robots and mounted so that the LEDs are visible. The radio should not be mounted near high noise devices like the leads to CIM motors or FP motors or near the 5 volt regulator. The bottom of the radio already has shielding so mounting it on metal should not be a problem but if mounted vertically, perf stock or lexan would be the preferred backing material. There didn’t seem to be a vast difference in signal between horizontal and vertical mounting although horizontal will likely give the best overall coverage.
When looking at the face of the radio, there is an antenna on both the left and right sides so don’t mount the sides against robot frame. Both antennas are used all of the time for both receive and transmit to achieve the highest throughput per 802.11 specifications. Secure the power lead in some fashion so that it won’t wiggle. A simple stickyback tie point mounted on the top of the radio, with a wire tie securing a loop of the power cord is the best option. I do not recommend hot glue as this makes repairs almost impossible when applied correctly. When not done correctly, the glue will give you false hope, likely mis-align the connector or damage the jack on the radio and the connector will fall out when you need it the most. If you choose to use a Radio Shack connector, insure it is the right dimensions. Often teams will use a connector meant for a larger diameter center pin. The result is noise on the power line during robot movement. Over time, as the connection becomes dirty, radio reset will be the result. If you are placing the radio near moving parts check clearances for all positions of the moving part. The metal of the moving part should not cover the radio when at rest or fixed position and it should not pass within two inches of the top or sides of the radio. Do not make severe bends in the ethernet cables, the max spec as I remember is 1" minimum bend radius for full bandwidth. Secure the ethernet cables near the radio so that they do not put strain on the jacks of the radio or pull out with robot movement. Putting a small loop in the cable will prevent any strain on cable or radio. Above all, make sure the 5 volt regulator is connected to the radio output on the PD and all wires are secure and insulated. Mount the regulator where it will be protected and does not move within the robot.

Al is right – we learned our lesson on burying the radio deep in the robot, down by the (electrically noisy) compressor and motors.

You should also make sure that you have a real CAT5 or better Ethernet cable, in good condition, connecting the cRIO and the radio. We had trouble with a mystery RJ45 cable that had flat satin cable rather than certified cable. I put that one in the trash as soon as I found it on the robot. At $2.61 each (on Amazon today) there’s no reason to not have a good one.

To emphasize a point Al made:

The tiny (2" long) antennas are mounted inside the box, at the right and left sides, oriented from front to back. And, metal is a good “blocker” of radio waves.

So, if you want POOR radio performance, then you must mount the radio:

  1. Behind metal
  2. On metal
  3. With the tiny antennas near metal

As far as the “Electrically Noisy” components mentioned above, these really and truly have very little effect at the GigaHertz frequencies used by 802.11 radios. The filtering on the DC input is sufficient, and the RF energy radiated by the motors does not reach significantly up into the GHz range - meaning you don’t need to care about it. But don’t forget, those motors are mead of metal, so see further above…

The ideal situation is to put the radio up high, on something non-metallic, like a strip of Lexan. Protected from injury, but not near metal. Run the power & Ethernet cables directly away from the radio, and not next to it (these contain metal - see way above…)