SRM Family of License-free Spread Spectrum Radio Modems

Q: Will information be secure when transmitted via SRM wireless modems?
A: The Data-Linc Group SRM series of modems are sophisticated devices that utilize complex technologies including adaptive frequency hopping, proprietary RF (Radio Frequency) packets, data compression and encryption, as well as a wide variety of configuration options. Unlike the 802.11 wireless radios designed for easy and universal access to which security can be applied, the SRM Series is designed for inherently secure and reliable communications. (For a more detailed explanation, read "Data-Linc Group SRM Series Wireless Security: Understanding Wireless Modem Data Transmission" in Articles and Technical Papers.

Q: How can the SRM be used on a DH+ or DH485 network?
A: The SRM supports asynchronous data formats in either a 10- or 11-bit word. In order to communicate DH+ or DH485, it is necessary to convert to DF-1 protocol. Allen-Bradley has several ways to do this and should be consulted as to the best method for a given application.

Q: Do I need an RF site survey before installation?
A: No. For most applications, as long as line-of-sight is maintained, the SRM RF technology will communicate without a problem. Sometimes it may be necessary to perform a visual survey to ensure line-of-sight by determining ideal antenna and Repeater locations. This procedure is certainly much easier— and considerably less expensive— than an RF site survey.

Q: What is the maximum number of Remote radio modems a Master can have on its network?
A: There is no limit to the number of Remote radio modems on a network. When an SRM is set as a multi-point Master, it will broadcast to any Remote. Only one Remote can talk to a Master at any given time, but the Master is not limited to the number of Remotes that it will talk to. Of course, the PLC protocol used may have a limit, but the SRM will in no way restrict network size.

Q: Why does the SRM6000 require line-of-sight?
A: It´s not a limitation of the SRM6000 but rather a limitation of the 900Mhz band employed by the SRM6000 Radio Modem. The higher a frequency, the less its ability to reflect off of or pass through obstacles. In some applications, where the range between modems is short, it may be possible to achieve very reliable communications without line-of-sight. Because there are many factors involved that can effect reliable communications under these conditions, it is our recommendation that the technical department at Data-Linc be consulted.

Q: Will the SRM interface with other Data-Linc Group modems?
A: Yes. All of Data-Linc´s modems have a standard RS232 interface port. Some are protocol transparent, and some require a 10- or 11- bit word. But they can all be linked to each other via their serial ports so that a network of wire modems with radio hops or radio modems with wire modem hops can be achieved.

Q: What advantage do I get by using the SRM6000 whose range is over 20 miles and a maximum port speed of 115.2 Kbps, when all I need to achieve is 2 miles or less at a port speed of, say, 9600 Kbps?
A: It is true that many applications do not require long range and/or high speed (115.2kbps). The SRM6000 uses frequency hopping spread spectrum technology. Each hop carries a data packet that is checked using CRC 32 bit error checking. If the packet is not correctly received and acknowledged, it is resent on the next hop frequency. This is all being done at the RF modem speed of 144Kpbs. At that speed, even if there is significant interference, the SRM6000 can pass data through accurately without jeopardizing the PLC communications speed of 9600bps or 19.2kbps. Because the SRM6000 can accommodate very long ranges at high speeds, all with a high level of reliability, when the modems are used at shorter ranges with lower speeds, operational tolerance margins provide an enormous safety buffer. This gives the system a level of reliability that is unmatched. Basically, with the SRM6000 you get the best of both worlds.

Q: Why does Data-Linc Group pre-configure the SRM? Is it too complicated to configure in the field?
A: No. Data-Linc Group does provide pre-configuration on all of its modems, but not because it would be too complicated to do in the field. We pre-configure the units so that the end-user or installer does not have to deal with yet one more task during the installation of an automation system. By providing this service, we increase our level of support to you, our customer - and that´s our number one priority. As to configuring the SRM, all it requires is a terminal program on a PC (or a terminal) set for 19.2Kbaud in a 10- bit word format. You simply push the configuration button and a menu screen is downloaded to the terminal where the changes can be made.

Q: Do I need separate units for Master, Remote and Repeater?
A: No. Any SRM can be configured as a Master, Remote or Repeater in point-to-point or multi-point systems. Configuration is performed at the factory for specific system applications, but can be as changed as needed in the field via a terminal program as described above.

Q: Do I need two radios and two antennas to make a Repeater?
A: No. A single SRM is all that is required for a fully functional Repeater.

Q: What is the difference between Data-Linc's AE485 and AE422and RS485/422?
A: Data-Linc uses "AE485/422 2-wire/4-wire" that is compatible with RS485/422 2-wire/4wire. AE, which stands for Auto Enable, is a Data-Linc proprietary technology that is compatible with RS485/422. The default for RS485/422 is receive mode. The AE function allows the device to transmit when data is fed to it without the need for a separate enable signal. Auto Enable is particularly important and beneficial in multi-dropped two-wire 485 and some four-wire 422 solutions. When interfacing with our products, wire count is most important. Please check with non- Data-Linc product manufacturers for their specifications. For further clarification contact Data-Linc at (425) 882-2206 or email techsupport@data-linc.com.

Q: Is there a standard for Ethernet?
A: The Ethernet network concept was developed by Xerox Corporation in the mid-seventies. Ethernet uses the Carrier Sense Multiple Access/Carrier Detection (CSMA/CD) access method.

There are several types of Ethernet systems. The most popular is the 10BaseT standard for Ethernet networks which uses AWG24 Unshielded Twisted Pair (UTP) cable for connection to the node. The physical topology of the standard is a star, with nodes connected to a wiring hub, or concentrator. Concentrators can then be connected to a backbone cable that may be coax or fiber optic. The node cable has a maximum length of 100 meters; consists of two pairs for receive and transmit and is connected via 10 BaseT plugs.

Q: Where did TCP/IP originate?
A: TCP/IP (Transmission Control Protocol/Internet Protocol) was developed by the US Government to build a heterogeneous (supporting multiple platforms) network across a wide area of the United States. In the early 1960's, The US Department of Defense (DoD) needed a wide-area, cross-platform communication system. Initially, the TCP/IP suite of protocols was used to interconnect government, military and educational sites together. Later, this protocol suite became a standard for commercial use.

Q: What is "Smart Spectrum^TM" technology?
A: For more information see FAQ Smart Spectrum.

Q: How can I get answers to some other questions I have about data communications and my application?
A: Email us at info@data-linc.com or call (425) 882-2206 during business hours Pacific Coast Time for a no obligation consultation.