RF Troubleshooting Tips

September 25, 2020 by Leslie Edison


You may have encountered an error code that provides RF identification and troubleshooting. There are several steps you can take to fix this problem. We'll get back to this shortly.

Radio frequency interference. Many factors affect the successful transmission or reception of a radio signal. The most common problems are radio interference, electromagnetic interference, cable and antenna problems.




This document discusses some of the main problems you may encounter when trying to wirelessly connect parts of a wireless network. RF communications problems between Cisco Aironet Wireless LAN components can be attributed to four main reasons:



Components Used


Firmware And Driver Problems

Sometimes the problem with the radio signal can be attributed to a problem in the firmware of the devices with which communication takes place.

If you are having wireless problems with your wireless network, make sure each component has the latest firmware or driver. Please use the latest driver or firmware for wireless LAN products. Use Cisco downloads (registered customers only) to get updated drivers and firmware.

Software Configuration Problemscare

If you have a problem with the radio, the configuration of the WLAN devices may be the cause of the radio failure. There are some parameters that need to be configured correctly in order for the devices to communicate correctly. If you do not configure the settings correctly, the problem is with the radio. These parameters include Service Set ID, Frequency, Data Rate, and Distance.

Service Set Identifier

Cisco Aironet WLAN devices must have the same Service Set Identifier (SSID) as all other Cisco Aironet devices in the wireless infrastructure. Devices with different SSIDs cannot communicate with each other directly.


The radios are tuned to automatically search for the desired frequency. The device scans the frequency spectrum to wait for an unused frequency or wait for transmitted frames that have the same SSID as the device. If you did not tune the frequency to Automatic, make sure all devices in the WLAN infrastructure are configured to the same frequency.

Coming Soondata Transfer Rate

The data transfer rate affects the coverage area of ​​the access point. Lower data rates (for example, 1 Mbps) may result in more distance from the AP than higher data rates. If the WLAN devices are configured for different data rates (expressed in megabits per second), the devices cannot communicate. Here are some common scenarios:


Radio communication between bridges is sometimes very long. As a result, the time it takes for a radio signal to travel between radios can become significant. The Distance parameter adjusts the various timers used in the radio protocol based on the delay. Enter the parameter only on the root bridge that communicates with repeaters. Distance to the longest radio link of all bridges is expressed in kilometers, not miles.

HF Problems

There are many factors affecting the success of sending or receiving a radio signal. The most common problems are radio interference, electricalrotary noise, cable and antenna problems.

Radio Interference

No license is required for 2.4GHz radios that use Cisco Aironet Wireless LAN devices. As a result, other stations can broadcast on the same frequency as your WiFi.

Spectrum Analyzer is the best tool for determining activity on your frequency. The Carrier Busy test, available on the Cisco Aironet Bridge test menus, replaces this article. This test gives a rough indication of activity at different frequencies. If you suspect that your wireless network is transmitting and receiving radio interference, turn off all devices operating on that frequency and run the test. The test shows all activity on your frequency and other frequencies that the device can operate on. This way you can determine if you want to change the frequencies.

Note. High error counters on the radio interfaces on the client, access point, or bridge indicate the impact of RF interference. You can also identify RFI by using system messages in the point logs.access (AP) or bridge. The result looks like this:


CRC and PLCP errors can occur due to radio frequency interference. The more radios in a cell (access points, bridges, or clients), the more likely these errors are to occur. For more information on the performance impact of CRC and PLCP errors, see the "CRC, PLCP Errors" section in the "Problems with Intermittent Connectivity to Wireless Bridges" article.

Electromagnetic Interference

rf identification and noise troubleshooting

Non-radio devices that operate in close proximity to Cisco Aironet Wireless LAN devices can occasionally generate electromagnetic interference (EMI). In theory, this interference can directly affect the reception and transmission of signals. However, EMI affects the components of the transmitter, not the transmission.

Isolate radios from potential sources of electromagnetic interference to minimize potential interference. If possible, keep the device away from such sources. Also provide consistent power to WiFi devices to reduce the impact of electricalto electromagnetic interference on the circuit.

Cable Problems

If you are installing bridges for long distance communications, make sure the antenna cables are no longer than necessary. The longer the cable, the greater the attenuation of the signal, which results in lower signal strength and therefore a smaller footprint. A tool is available to calculate the maximum distance at which two bridges can communicate, based on the combinations of antennas and cables used. Download this tool from Antenna Design Table (Microsoft Excel format).

As with any network cable, the antenna cables must be properly installed to keep the transmitted signal clear and free of interference. To ensure your cables meet their specifications, avoid the following:

Antenna Problems

Use the Antenna Design Spreadsheet (Microsoft Excel format) to calculate the maximum distance over which two bridges can communicate, depending on the antenna and cable combinations used.

What causes RF interference?

Interference occurs when unwanted radio signals interfere with the operation of your television, radio, or cordless telephone. The two most common causes of interference are transmitters and electrical devices.

In many cases, line of sight (LOS) is notseen as a problem, especially with wireless devices that communicate over short distances. Because of the propagation nature of radio waves, devices with omnidirectional antennas often communicate successfully from room to room. The density of the materials used in the construction of a building will determine the number of walls that an RF signal can pass through while maintaining adequate coverage. Here is a list of the main effects of signal penetration:

When connecting two points (for example, an Ethernet bridge), consider distance, obstacles and antenna location. If you can install the antennas indoors and the distance is close (a few hundred feet), you can use a standard dipole or magnetic mount with a 5.2 dBi omnidirectional antenna or yagi antenna.

Use directional antennas with high gain over long distances (at least half a mile). These antennas should be as high as possible and above obstacles such as trees and buildings. If you are using directional antennas, be sure to orientate them the same so that their main petals are facing each other. With line-of-sight installations and Yagi antennas, distances of up to 40 km at 2.4 GHz can be achieved using satellite dishes, provided that line-of-sight is maintained.

Note. The Federal Communications Commission (FCC) requires professional installation of high gain directional antennas for systems that are licensed for point-to-point operation only and whose total power is equal to the effective isotropic radiation output (EIRP) +36 dBm above. ... EIRP is the total power transmitted to the receiver. The installer and end-user must ensure that high-performance systems only operate point-to-point.

Client Issues

How do you fix RF interference?

Install RFI filters in the signal path.

When the spurious RFI exceeds about 20 MHz, ferrite sheaths can be effective and can be easily installed on the outside of the cable. In most cases, they work best when attached to or near the receiving end of the cable.

Troubleshooting the Cisco Unified Wireless Network Client describes the various issues you may encounter when connecting a wireless client in a Cisco Unified Wireless environment, and the steps you can take to troubleshoot the issue. and solve these problems.

OthersThe Reasons For The Decrease In Signal Strength

Even if LOS is set between wireless connections or there is no Fresnel lock, you can still get a low signal level. This problem can have several reasons.







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