2. Do I always need line-of-sight (LOS)?

No. The radio waves used by the OMNEX Trusted Wireless™900MHz radios pass through all kinds of obstructions just like your AM/FM radios. Wood, drywall, concrete and steel all affect the ‘propagation’ properties of radio waves differently.  Wood structures are the easiest to pass through, though steel structures sometimes act as shields.  With this in mind, to ensure your radio waves penetrate or escape a conductive metal enclosure such as a steel electrical enclosure, or to get the signal into or out of a robustly build steel building, we recommend mounting the antenna on an external surface.

3. How far will a typical 1 Watt OMNEX Trusted Wireless™ 900MHz radio go?

That depends on the gain of the antennas used and the nature or density of obstructions in the path. But here are some guidelines:

• 1000 feet in a heavily obstructed industrial or municipal setting using ¼ wave 0dB gain omni-directional antennas
• 1000 feet to 1 mile in mildly obstructed industrial or municipal settings using ¼ wave 0dB gain omni-directional antennas and appropriate ‘common sense’ antenna placement
• 1-2 miles LOS with ¼ wave 0dB gain omni antennas
• 1 mile through a dense forest of hardwood trees or across an industrial plant using 6dB gain antennas (on both ends)
• From 2 to 20+ miles if you have LOS and you increase the antenna height as the distance increases

4. How do I know if the OMNEX Trusted Wireless™ radios I want to install will get reception and which antennas to specify?

We recommend using the following guidelines:

• If the distance to be covered is less than 1000 feet, no test is required. In a very high percentage of applications the radios will work out-of-the-box with 0dB gain antennas regardless of what is in the radio’s path.  We call this the ‘No Worry Zone’; anyone can make an OMNEX radio work under these conditions.
• From ½ to 2 miles, test the link with a demo system or the radios to be installed.  By checking the Receiver RSSI output with a voltmeter (see manual) determine where the antennas need to be mounted for the maximum RSSI and/or check if a higher gain antenna would be helpful.  We call this the ‘Common Sense Zone’; anyone can make an OMNEX radio work with a little forethought.
• Beyond 2 miles, get the GPS co-ordinates of your radio sites from Google Earth and conduct a pathloss study.  (OMNEX can perform a pathloss study for you, if required.)  We call this the ‘Performance Zone’ where professional help is often useful.

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5. How far can the antenna be located from an OMNEX radio?

Generally 200 feet is a practical maximum.  Like all cable, as the length of your coaxial RF cable increases so does signal loss.  Similarly, there are several types of coaxial RF cable which vary in attenuation properties depending on quality and price.  Rule of thumb: running antenna cable is very similar to running 120V wire, as the length increases you must increase the cable diameter to compensate for the voltage (signal) loss.

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7. How do I know if my OMNEX radios are linked?

The OMNEX Trusted Wireless™ 900MHz radios have a dry contact labeled ‘RF Link’. When a receiver is linked with its designated transmitter, the RF Link contact closes. When the link is lost, the contact opens. Upon loss of the link, the I/O will either maintain last state or go OFF depending on how it is configured/wired (see manual).  The RF LED will flash slowly if there is no link.

8. When is the best time to test a radio link?

Under conditions when the most obstructions are in place.  This means in the spring/summer if there are leaf bearing trees (add a 5-10dB fade margin if testing in the winter, see manual for details) or when the doors to a facility are closed (if transmitting from outside to inside a building).

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11. What happens to reception if a new building is erected or trees/bushes grow up between two installed radios?

Adding more molecules for radio waves to pass through (i.e. air being replaced by a building or trees) will naturally cause attenuation of the signal.  This is why we recommend that radios be installed with a 10-20dB fade margin.  The fade margin is the extra signal strength beyond what is necessary for reception.  On OMNEX radios, the RF LED remains ON solid when you have a greater than 20dB fade margin; it flickers rapidly when the fade margin is less than 20dB, and it flashes slowly when threshold is reached and the link is lost.  Using the example of leaves, if two radios are installed in the winter time and the RF LED is solidly ON, leaves filling the trees in spring will likely not affect the link.  If, on the other hand, the RF LED is rapidly flashing during a winter installation it would be a good idea to adjust antenna placement or increase antenna gain to get a solid ON so that you have enough margin to take care of additional leafy attenuation in the spring.

12. How many OMNEX radios can operate in the same area?

Hundreds.

13. Do I have to coordinate radios operating in the same area?

Wire-in, Wire-out Radios: If the OMNEX Trusted Wireless™900MHz radios come as a pair – transmitter and receiver – they will be programmed from the factory.  If you are adding more receivers to create a point to multi-point system, you can coordinate the radios by using the HopKey provided (see manual).  No software programming is necessary and OMNEX assigns radio ID’s, hop patterns, etc. in a manner that eliminates system overlap.  

Serial Data Radios: OMNEX serial data radio systems are configured by the end-user and integrators with user-friendly configuration and diagnostic software.

14. What is multi-pathing and why don’t the OMNEX Trusted Wireless™  900MHz radios have two (2) antennas like most WLANs?

Multi-pathing is a condition where radio waves leaving a transmitter take different paths to a receiver (due to reflections off of obstacles) and end up reaching the receiving antenna out of phase with one another.  As a result, if two or more radio waves arrive out of phase at one antenna, chances exist that the opposing waves could cancel each other and result in a ‘nulling’ of the radio signal (no reception). WLAN radios use two antennas to try to overcome such nulls by placing the receive antennas in two physically different paths. Rather than physically changing the path, frequency hoppers overcome multi-path null conditions by constantly changing frequencies.  Why does this work?  Since different radio frequencies have different wave characteristics, signals sent on different radio frequencies will not behave the same in any given environment.  This means that a null occurring at one frequency, in a highly reflective refinery for example, will not occur on another frequency because the wave properties are different.  This twist of physics is what makes FHSS radios immune to multi-pathing when signal reception is assessed over time. 

15. Are these radios susceptible to interference from cell phones, two-way radios, etc?

No.  Cell phones operate on frequency bands – typically 860-890MHz and 1.8GHz – outside the ISM 900MHz & 2.4GHz bands where industrial radios operate.  The fixed frequency voice radios that plant personnel use often operate in the 450MHz range.  In terms of off-band interference, the OMNEX Trusted Wireless™ 900MHz radios use narrowband filters to keep unwanted signals out.  That said, other ISM band radios operating within the 900MHZ band do have the potential to cause interference, but because of the nature of frequency hoppers, if a collision occurs on one frequency, milliseconds later the radios hop to other frequencies where data can be updated.  

16. What is the I/O update/response time?

For the OMNEX one-way systems, response time is 27milliseconds for digital signals and 270milliseconds for analog signals.  However, a conservative engineer installing these radios in a high interference environment would likely take into account that some transmissions on specific frequencies may be interfered with and allow for two or three transmissions before an error-free signal arrives at the receiver. In this case, the engineer could multiply the update times by two or three.  Response times for two-way systems are a little longer.

17. Why the different response times for digital vs. analog signals?

This reflects the desire to reduce power consumption for solar power or battery powered installations.  When radio transmits less frequently it consumes less power.  This is fine for analog values (typically more slow moving for tank level, etc), however, if an alarm condition occurs – a digital signal – it is important that the update be given on the next hop.  With this in mind, the transmitter monitors the status of it’s inputs and if a digital input changes state, the transmitter increases its update rate to 37 per second.  Otherwise (for analog signals) it updates 3.7 times per second as long as the digital signals maintain their last state. 

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