Special Concerns for Sensors on Communications Towers

It is not recommended to mount NRG equipment on radio transmission towers. A wide range of interference possibilities exists.

Exposure to Radio Frequency

Interference can cause false counts which give incorrect high wind speeds. Also, currents themselves can cause damage, or can get rectified and cause offset voltages in wind vane circuits.

If you decide to install the equipment on a transmission tower, here are some considerations and recommendations:

Tower Overview

When mounting NRG sensors on radio transmission towers, determine whether the entire tower is being used as an antenna, or if the tower is being used to hold an antenna that is attached to the top of the tower.

If the whole tower is being used as an antenna, or if the sensors or sensor cabling are mounted too close to an antenna, Radio Frequency Interference (RFI) can easily affect with your wind data.

Sensor Placement

The user should consult with the tower engineer to gain an understanding of the antenna radiation patterns.

Sensors should not be mounted directly in the near radiation field of any antenna.

Remember you still want to keep the sensors out of the tower's aerodynamic wake, at least for the prevailing wind.

Sensor Connections, Shielding and Grounding

All sensor cables should be shielded.

Use cables like Carol C1332, which is 3 conductor, 20 AWG, with a full braid shield.

Shielding from induced magnetic effects is desired, not just against capacitive coupling. In order to accomplish this, connect both ends of the shield, and bond to known reliable grounding points in order to prevent ground loops and to control lightning-current-related voltage rises, in coordination with the shielding and bonding of the other services on the tower.

Keep dressed leads to the minimum possible length.

Logger grounding is essential for protection and lowering the noise floor.

Coordination of grounding and bonding for lightning protection

It is preferred to be well shielded, and bonded to the local RF ground. However, huge voltage drops during lightning events can cause damage. Do not provide a path to route lightning currents to somewhere that will damage other equipment. Make sure the logger's ground has a suitable point to tie to.

Signals and Filtering

In some installations, it makes sense to use the NRG #40H anemometer (Digital Anemometer SCM is required) so even low speed signals are high amplitude.

Low pass filter the inputs HEAVILY. The frequency of interest is only 0 to about 100 Hz. It is OK to distort the waveform. For example: an RC filter with R = 10 K, C=0.1 uF has a corner at 160Hz. LC filters such as CLC "Pi" or LCL "T" can be added to each input and to the power wire going up to the sensors.

Make sure all the RF suppression components have good RF grounds to tie to. To test this, make sure speeds read zero with the anemometer stopped, and the station on the air.

It is also a good idea to look for unexpected DC offset voltages by metering the input circuits.

RF coordination / considerations for iPacks

Is the iPack cell phone going to interfere with any other service on the tower? Are services on the tower going to jam the iPack?

It may be necessary to fall back to a heavily RFI suppressed land line and a dial-up iPack or change your iPack antenna type.

Our equipment was tested for interference during our application for a 'CE' mark, so we can supply this information upon request. Our Symphonie logger is also certified for compliance with FCC standards (the FFC is the government agency that oversees broadcast-related issues in the USA).