Overcoming Common Data Communication Problems

Data communication (also referred to as telemetry) is an increasingly integrated part of many data collection systems.

environmental data communication diagram

Getting data from one place to another is not trivial. Many communication system design and engineering variables for telemetry need to be addressed, including:

data format and size, and from what type of sensors or equipment;
how often the data needs to be transmitted;
the transmission environment and overall distance it has to travel
the type(s) of terrain and foliage the signal will encounter;
the data communication protocol used;
available radio frequency choices available for each site and the related signal strength;
selecting the optimal combination of radios and antennas;
the position and mounting of the antennas.

Stevens Water has been specializing in telemetry systems for data transfer since the invention of the Stevens Telemark in 1937, which allowed users to call in from their telephone and receive water stage level information.

Since then, Stevens has designed radios and integrated most major communication systems for customers, including UHF/VHF and spread-spectrum radios, cellular data modems, GOES satellite transmitters, and Bluetooth systems, and has vast experience troubleshooting many of the common problems that can cause issues with a telemetry system.

The list provided below is a sample of the most frequently experienced issues that need to be considered with a telemetry system for remote data collection. For professional help, please contact Stevens Water at (800) 452-5272 or email info@stevenswater.com to discuss your telemetry application needs.

1. Make sure you select the right radio and antenna for the job.

There are many radios on the market today, covering all wireless spectrums and their approximate coverage area:

Radio Type	Typical Communication Range	Frequency
Bluetooth	Class 1: up to 100 meters Class 2: up to 10 meters Class 3: up to 1 meter	2,402 - 2,483.5 MHz
Zigbee	250 ft – 4,500 ft depending on radio type	868 MHz (Europe) 915 MHz (USA and Australia) 2,400 MHz (worldwide)
Spread-spectrum radio	5 miles	902 - 928 MHz & 2,400 - 2483.5 MHz ISM Bands
VHF/UHF radio	30 miles	30 to 300 MHz (VHF) 300 to 1,000 MHz (UHF)
Cellular radio	Within approximately 30 miles of cellular tower, but coverage is essentially world-wide once the data is on the cellular network	824 - 894 MHz (USA AMPS) 1,850 - 1990 MHz (USA digital PCS) 1,710 - 1840 MHz (Europe digital DCS)
LEO Orbcomm Satellite radio (global coverage)	Global	148 - 150.05 MHz (uplink) 137 to 138 MHz (downlink)
GOES Satellite Transmitter	GOES footprint covers 1/3 of Earth’s surface	400 MHz – 402 MHz

Selecting the right radio for the job depends on a number of variables including the radio’s frequency of operation, available power output, the terrain, the data communication distance, and the receiver sensitivity. Also important is selecting the antennas that support the appropriate frequency, gain, and power ratings for the radios being used. The selected radios should be configured and placed within the normal operating range for their frequency; otherwise data will not be received reliably.

2. Configure the radios, loggers, and sensors properly.

Properly configuring the radio according to the manufacturer’s instructions is very important because one wrong setting can cause the entire system to not function properly. Care should be taken to ensure the radio is properly communicating with any sensors or data loggers that are connected to it, and that the proper baud rate for transmission and other port settings are correct. Stevens can help with the selection and configuration of radio equipment for your communication sites.

3. Properly power the radio and other equipment.

Improperly planning for power consumption of the radio and any other equipment at the site can have the potential to cause a loss of data if the radio stops transmitting because the power budget was calculated incorrectly and the system’s battery was drained to the point of automatic shut down.

If a site doesn’t have AC power available, create a power budget taking into consideration the maximum load that can be drawn when sensors are taking readings, and when the radio is powered on to transmit, which will use much more energy than stand-by mode. Stevens can assist with the calculation of a power budget for your site.

4. Ensure the antennas are correctly installed, pointed in appropriate direction, are free from obstruction and have the appropriate ground plane.

After selecting the proper radio and antenna combination, care must be taken to ensure the antenna is pointing in the proper direction of the base station or repeater. Simply having the antenna more than a few degrees off may be enough to cause data transmissions to fail if using a directional antenna such as a yagi-style or GOES antenna. An omni-directional antenna needs to be polarized correctly.

Depending on the antenna type and location of the station, geographic features such as hills and other terrain may cause signal degradation, as well as man-made objects such as buildings. Foliage growth and trees can also cause problems. For example, certain pine needles do attenuate a 900 Mhz signal and can cause interference with radios that operate in that band.

Depending on the location, a radio/RF site survey may be required to determine the optimal radio settings and how to best place antennas and other equipment for maximum signal propagation. Stevens can recommend if this will be necessary for a successful system installation.

5. If the radio is a cellular data modem, ensure the data plan is activated.

Some types of radio services, such as cellular data modems, need to first have data service provisioned and activated with a wireless carrier (such as AT&T or Verizon in the US). Additionally, this data service bill will need to be paid each month for service to remain active. If the account is shut down, the radio will no longer be allowed to transmit data over the cellular network.

Certain regions also place a lower priority on cellular data transmission when the overall cellular system is being used at peak capacity. Due to the popularity of the Apple iPhone and the bandwidth this device consumes, the AT & T GSM system is heavily used at times and it is common for data packets to be dropped.

It is also important to ensure that the radio you select is compatible with the cellular networks in your area. This information is usually provided on the data sheet for the radio, and most radios come in multiple versions to support the most popular networks. GSM networks (such as AT & T) will require a radio that can be provisioned with a SIM card from the wireless carrier, which identifies the radio to the network and grants the radio access to communicate over the network. This SIM card will be provided by the wireless carrier upon activation of the data account.