Choosing the right telemetry technology for your network is extremely important and there is no single technology that is right for all applications. Several variables like path distances, terrain, link availability and licensing must be considered. Another important factor is the demanding nature of seismic data communications which requires link performance to be better than 99.9%. Unlike other information which may be transmitted through email or file transfer, seismic data must be communicated continuously with the low latencies of real-time processing. In many cases the best solution is to combine a number of technologies to achieve the required network design.
| Technology | Frequencies | Typical link distances | Comments | | Fixed frequency RF | 380-512 MHz | 20 to 120 km | Full duplex, licensing required | | Spread spectrum | 902-928 MHz | 1-25 km | IP LAN, unlicensed* | | Spread spectrum | 2400-2483 MHz | 1-25 km | IP LAN, unlicensed* | | Spread spectrum | 5800 MHz | 1-15 km | IP LAN, unlicensed* |
* Spread spectrum is not permitted in some countries and is licensed in others.
RF communicationsNanometrics fixed frequency (FF) RF solutions are used by customers requiring real-time telemetry links extending up to 100 km . This system typically operates on licensed frequencies in the 380 to 512 MHz UHF range. UHF FF telemetry, while requiring licensing and knowledgeable RF network designers and installers, is often easier to implement than many “plug-and-play” spread spectrum systems. UHF FF telemetry is more forgiving of path obstacles and offers greater range than spread spectrum systems. Before we go to the field our engineers will simulate each telemetry link, calculate the required margins and design the link to meet the required 99.9% availability. Spread spectrum
RF spread spectrum networks are attractive and often touted as the best solution for RF telemetry. This is often due to the plug-and-play nature of the equipment set-up and the lack of licensing formalities. In reality, these networks are often more difficult to deploy due to the higher frequencies at which they operate. RF losses in cables, connections, lightning protection and the free space propagation over the transmission path must all be included in the ink budgets.
While many manufacturers will quote distances such as 60-80 kilometers, in actual operation it is difficult to find unobstructed paths and at the same time providing enough fade margin for the network to provide reliable real-time data. Spread spectrum is very attractive when deploying short range, <18km, true line of sight, unobstructed links. This technology can be very effective when combined with Libra VSAT to build small arrays around VSAT remotes. VSAT communications Satellite communications have a number of distinct advantages over terrestrial RF types. VSAT does not suffer from the line of sight problems of terrestrial communications as data are transmitted directly up to a geostationary satellite. Any location with a clear view of the satellite in the sky is a suitable remote site location. VSAT also offers a solution to long distance communications. For more of VSAT communications go to the Libra section of this web site. |
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Last Updated on Thursday, 01 December 2005 07:34 |
