S3 Satcom Guide to Small Antenna Tracking Systems · presence for monitor and control. Small antenna tracking systems have been on the market for years. They are installed ... the

S3 Satcom Guide to Small Antenna Tracking Systems

THE OBJECTIVES OF THIS GUIDE ARE:

to provide an insight into the areas that need to be considered when selecting a small antenna tracking system.

to illustrate the compromises made by some small antenna tracking system suppliers to keep the cost low, and the alternative approaches possible.

to describe how the S3 Satcom Satsio offer great value for money by delivering small antenna tracking without these compromises at an affordable price.

To keep the cost low, traditional small antenna tracking systems have had to compromise on their design. As a result, they do not accurately sense the antenna position, optimnise their pointing, nor accurately position their polarization. And they require manual adjustment and offset entry, and local presence for monitor and control. Small antenna tracking systems have been on the market for years. They are installed and in operation all over the world, fulfilling a range of requirements from tracking inclined orbit satellites to automatically re-pointing at different satellites on-demand. You’d therefore be forgiven in thinking that the list of issues highlighted are of no concern and that there is not a lot to consider when selecting a small antenna

systems. You may also think that with such a well proven set of products in the market there was little to no room for developments that could improve their performance and extend their range of applications and operations. But, there are many issues that do indeed need to be considered and in each of these there have been significant developments in recent years. This S3 Satcom Guide to Small Antenna Systems is written to provide an overview of the areas that you should consider when selecting the right small antenna tracking system for your requirement. It will highlight some of the development specifically undertaken by S3 Satcom to address the list of issues with existing small antenna tracking systems.

It will also consider the commercial aspects of investing in a small antenna system, illustrating that the above improvement can be delivered within the budget for such a system.

As a result of reading this guide you will appreciate the benefits designed into the S3 Satcom Satsio that make it the most precise, versatile, robust and cost effective small antenna tracking system on the market.

Introducing the world of small antenna tracking systems:

Introduction


Accurately sensing your antenna position

One of the key requirements of any antenna tracking system, is to know where your antenna is pointing at any one time, and to be able to accurately move it as required to new positions. The ability to accurately detect the antenna position is critical. The approach adopted by some small antenna tracking systems is to use reed switches with magnets to detect pulses as actuators move. While these are low cost, they lose position over time. Indeed, they can be observed to count pulses as the wind moves the antenna, even though the antenna subsequently moves back to its original position. Such small errors will build-up in a monitoring system until significant offsets can be observed. Then manual intervention is required to re calibrate the system. An alternative technology adopted by some tracking system manufacturers is the resolver. A resolver works by passing a sine wave through one rotor coil and measuring the induced sine wave on two other coils that are at right angles. This device does provide an absolute angle, which means that the issue of increasing errors seen in the reed switch approach is overcome. But the alignment of the coils is notoriously difficult and as a result resolvers are either not very accurate (those within the small antenna tracking system budget), or very expensive (those outside the typical budget). Another accurate option, which is relatively simpler to build and therefore lower cost, is to use incremental optical encoders. Standard incremental optical encoders can provide sufficient accuracy and resolution, but they are not absolute like the resolver approach. If power is lost to the system, you will need to re-calibrate the system at power up. Alternatively you’d need to invest in an

un-interrupted power supply to keep the power on at all time, so as not to lose the knowledge of the antenna’s position. To overcome this limitation absolute optical encoders can be used. Absolute optical encoders read the actual antenna position, rather than being an incremental count. If power is lost to the system, the position can be read with great accuracy at power-up without needing to re-calibrate. But absolute optical encoders with the required resolution are expensive. Their high cost has as a result prevented them from being an economic option for small antenna solutions. This type and resolution of absolute optical encoder is usually only seen on very large antenna tracking systems where the price is not so much of an issue. S3 Satcom has resolved this issue by designing their own robust and accurate absolute optical encoder in-house.

Special test procedures have been developed to ensure that the encoders provide the necessary level of resolution, accuracy and reliability (even in adverse environmental conditions). And all this is delivered at a price that is attractive for small antenna tracking system.

The S3 Satcom Satsio is supplied with 16-bit absolute optical encoders as standard, at a cost suitable for a small antenna tracking systems. Satsio therefore has the highest level of position sensing precision of any small antenna tracking system on the market, and reads the position of the antenna even after a power loss.

One difficulty when installing a motorized mount, is to ensure that the azimuth motion is actually in the horizontal plane and that elevation motion is truly in the vertical plane. The effect of having motion axes which are not accurately aligned to the horizontal or not orthogonal to each other is that positioning errors are introduced. If the axes of the antenna mount are not truly independent then movement intended to be only in azimuth, results in an unintended small movement in elevation–and vice versa. The effect of this is that when the antenna is automatically instructed to point at a theoretically correct azimuth and elevation for the selected satellite, the user will find that it is not precisely pointing at the satellite because of misalignment of the axes.

To overcome this error the operator then has to manually adjust the antenna until it does accurately point at the satellite and store the new position for that target in the antenna controller database for future reference. This process needs to be repeated for every satellite that is to be pointed at—an extremely labour intensive operation, particularly if multi-satellite pointing operation is required. It is also necessary each time a new satellite is launched that may need to be accessed. And this is the only method currently used to overcome this error. No small antenna mount has been available on the market that enables this error to be mechanically corrected at installation, thereby removing the need for operators aligning antennas and entering offsets.

That was until the S3 Satcom Satsio entered the market... The Satsio mount has a mechanical assembly (see photo) that enables a one-off adjustment to ensure that the azimuth acts exactly in the horizontal plane at initial system installation (providing the king post has no more than a 5 degree offset to start with). This is a task that takes only a few minutes with no more specialist equipment than a spirit level and a wrench. The mechanical design of the Satsio mount is therefore such that the elevation movement is always orthogonal to the azimuth movement. With Satsio, operators never have to enter azimuth or elevation offsets. The installer will have adjusted the mount so that the azimuth is truly horizontal at installation and operators never have to worry about it. And this accuracy is available over a very wide range, with an azimuth range of 120 degrees and an elevation range from 5 to 85 degrees. The slew speed for the movement is 1 degree per second for both azimuth and elevation.

When the Satsio system downloads information on a satellite’s position, even a new one just in service, it can automatically control the antenna to precisely and accurately point at that satellite without the need for any manual adjustments in azimuth or elevation.


Ensuring truly horizontal and orthogonal movement


Accurately aligning your antenna

A small antenna tracking system is only as good as the accuracy of the tracking it achieves. Yet most tracking systems on the market do not optimise their alignment. Most small antenna systems use the “beacon step track” method to track satellites in inclined orbit. In beacon step tracking, the power of the beacon is measured at the current antenna position. The system then moves the antenna by one small “step” and measures the beacon power again. If it increases, it moves the antenna another step in the same direction. If it decreases it moves in the opposite direction. This continues until the beacon power measured falls after one of the step movements. The tracking system then moves the antenna to the position where the beacon power was highest. And so the pointing is “optimised” in discrete steps. But of course, the optimised position is unlikely to actually be on one of these discrete steps. It is likely to be somewhere in between. So, how can the step tracking be optimised? The Satsio system includes a beacon based tracking method called “P-Step Tracking” that optimises step tracking. In the same way as standard beacon tracking it measures the beacon power in steps. But when the best discrete position is found, the measurements taken to get to this position are analysed and the optimised position between the discrete positions calculated. Using the very accurate 16-bit absolute optical sensors, Satsio can then align the antenna between the discrete positions to optimise the pointing to within 0.01 degree. All sounds good. But then there is another issue...

On a small dish, the beacon signal required for step-tracking is sometimes not receivable as it may be on a different polarisation to the receive system, or be suffering from a carrier to noise ratio that is too low for step tracking to work well. In both cases step tracking is either not possible or large signal level variations become a problem. So, are there any other approaches to tracking that overcome these problems? The Satsio controller incorporates a second tracking approach, called “NORAD tracking” that completely removes the need to receive the satellite beacon. This is the preferred Satsio tracking method that S3 Satcom recommends. NORAD tracking works by using a mathematical model to predict the exact location of a satellite at any given instant in time. The American Department of Defence tracks every object in orbit, and to comply with the Freedom of Information Act publishes the data on the Internet. The Satsio controller regularly retrieves this information (the Ephemeris data) and uses it every few minutes to calculate the pointing angles for the satellite—extremely accurately—even for inclined orbit satellites.

An operator can therefore select a satellite and the Satsio system will automatically move to point at the optimal position for that satellite, without even needing a beacon receiver. This approach is so successful, that S3 Satcom regularly install Satsio systems without beacon receivers, with the customers preferring to rely on the accuracy of NORAD tracking.

In conclusion, the Satsio system provides two methods for more accurately aligning small antennas, ensuring that the optimal positioning and smoother tracking is achieved at all times.

Not all satellites fly with their X-polarisation aligned with the equator, yet most small antenna tracking systems on the market are only motorised and automated in 2-axis. While many satellites fly with their X-polarisation aligned with the equator, a convention that makes the maths of calculating the polarisation angle easy, some satellites break this convention. For example, Eutelsat typically flies its satellites with a 3.5˚ offset to the equatorial plane, and Astra at a 7˚ offset. However for some satellites the exact offset is unknown. When multiple satellites are to be accessed by an antenna, the ability to adjust the polarisation is therefore essential, but rarely included in small antenna tracking systems, and where it is offered, it is usually inaccurate.

As a result, the polarisation usually has to be adjusted manually. Typically this is achieved by nulling out (minimising) the beacon on the opposite polarisation to ensure correct alignment. This though is a very labour intensive process that you would not want to repeat for every satellite you wish to access. Ideally you want to automate the polarisation adjustment, so that as you select a new satellite to point at, the motorised polarisation applies the appropriate offset. The problem is that there is no published data on the Internet for the polarisation angle of each satellite, nor is there any tracking method that has been proven to be effective.

Satsio though addresses this by calculating the theoretical angle for each satellite, which is accurate enough for the majority of satellites. And for those few that it is not, Satsio provides the ability for the operator to store offsets for any satellites accessed that do not conform to this model.

As a result, Satsio has the best automated polarisation angle adjustment capability on the market. For the majority of satellites, the pre--stored offsets will automatically be accurate enough to operate. For the others, a small manual adjustment and storing of the actual offset is all that is required


Adjusting the polarisation


Web based monitoring and control One challenge when operating satellite communications systems, is the need to be able to access each site, to check its status and make changes. This is particularly true for remote unmanned installations, and in multi-site operations distributed over wide geographies. Most small antenna systems available on the market require the operator to be physically at the location of the system—to check the status and make adjustments on the front panel of the controller. Each system is also standalone. So to check and adjust several small antenna tracking systems over several sites, is a very time consuming and expensive task. Ideally what is required is a low cost remote monitor and control unit that can connect to multiple small antenna tracking systems, preferably on multiple sites. To address this need, an integrated Web Server is supplied as standard in the Satsio controller. The Satsio Web Interface enables operators to access Satsio systems to monitor their status, and to take control of the system (together with any external devices attached to the Satsio Controller—see next section) over the Internet or Intranet. From any web client the operator can continuously monitor the Az/El/Pol angles, beacon levels (if a beacon receiver is installed) and summary alarms. The operator can adjust the antenna position via direct angle entry or by using increment / decrement buttons. In fact every operational parameter can be accessed remotely. The operator has access to a list of satellites, which is always completely up to date and includes any new ones in service, on a scrolling list.

The required satellite can be selected and the Satsio system will then move the antenna to precisely point at that satellite—even those in highly inclined orbits. In addition, the web client can be used to download firmware updates for additional features and fixes without the need to return the Satsio controller to the factory. Full configuration backup and restore is also available through the web interface. With such a potentially easy to access system, security is of course paramount. Control of the Satsio system is therefore fully password protected to ensure that only authorised personnel can make changes. But surely t here is a large overhead in terms of loading software onto remote workstations and keeping them up to date and synchronised. And the cost of the software licenses for multiple remote sites would be prohibitive. Not at all.

This monitor and control capability is via a standard web browser. No extra software is required on the remote PC. When one remote workstation makes adjustments to the system, all workstations will see that change. One Satsio web interface can monitor and control unlimited numbers of Satsio systems (one at a time) anywhere in the world, provided that each can be accessed through the internet. Conversely, multiple Satsio web interfaces can be deployed to control the same Satsio.

With its web client the Satsio system offer an unrivalled level of flexibility and access to Satsio systems at one or more sites. Every operational parameter can be accessed remotely from anywhere in the world. And all this is included as standard in Satsio, at no extra cost.

Integrating small antenna tracking systems into wider satcoms systems is often a challenge. While all the monitoring and control functionality for its own mount are included, rarely has any thought gone into what more could be done to support the satcom operator with the same system. As standard all tracking systems will have the power and control interfaces between their controller and the antenna mount motors, positioning sensors and beacon receiver. Satsio also has all these as standard, including both mains and +24V DC power input, Az/El/Pol DC motor drives, Az/El/Pol absolute encoders and dual beacon receiver inputs. Of note though is that it also has an external (opto isolated) emergency stop loop interface.

But the issue is not integrating a small antenna tracking system’s controller to its own mount, it is how to integrate such a system with the wider satcom system. The Satsio rack mount controller, provides hardware integration of external devices through a variety of standard interfaces, enabling a comprehensive M&C system to be operated at no extra cost. These interfaces can be accessed from the Satsio controller or from the remote web interface. Custom names for each can be entered, making Satsio a highly flexible monitor and control system beyond just the small antenna tracking system. Eight (8) off 5 Amp C/O relay contacts are provided for control of external devices such as waveguide switches. 32 independent opto isolated inputs are provided as standard. 2 analogue voltage inputs are provided, which are 12-bit encoded.

An RS485/RS232 serial interface is provided for interfacing to external devices. +24V DC power output is provided for external equipment (LNBs, Beacon receivers etc).

And an RJ45 to collect the NORAD ephemeris data from the internet, and for remote control connection to a local area network or the Internet. 2 USB ports are provided for an external flash drive. As well as offering the capability to monitor and control external devices and systems, Satsio includes as standard, a fully featured protocol for connection to a site wide Integrated Monitor and Control system. This means Satsio can be integrated as part of wider monitor and control systems if required.

As standard, the Satsio system offers far more monitor and control functionality and capability to external systems and devices than any other small antenna controller in the market. It also supports a fully feature protocol for integrating with external monitor and control systems.


Integrating with external products and systems


Integrating with external products and systems Introducing the world of small antenna tracking systems:

Considering the cost implications There are a number of areas of cost to consider when selecting a small antenna system, including the capital investment cost, the lifetime cost of ownership and the cost of expanding for additional capability. CAPITAL INVESTMENT When comparing the initial purchase cost of various small antenna satellite systems the complete system cost should be taken into account. This includes the mount, controller, ancillary equipment and installation services cost. A tracking system that uses the beacon step tracking approach requires a beacon receiver and PLL LNBs to receive the beacon. Satsio using NORAD tracking does not need a beacon receiver and if the carriers are large (>1MHz) it can use cheaper DRO LNBs. A tracking system that does not have truly horizontal and orthogonal mount axis will need to have manual offsets entered for each satellite to be pointed at. Satsio, with its inherently orthogonal and easy to make horizontal mount requires no such configuration. In short, a full Satsio system with ancillary equipment will cost about the same as a inferior competitor product, and will be quicker and easier to install. COST OF OWNERSHIP Cost of on-going operation and support of the system is an important consideration. For unmanned or multi-site installations, tracking systems that require personnel to physically be at the installation site will incur costs as support staff travel to these sites. Satsio, with its web client, provides the ability to monitor and control small antenna systems remotely over the internet, with full control of all parameters. One engineer can monitor and control Satsio systems across multiple sites from one location

A tracking system that uses reed sensors or non-absolute optical sensors will need re-calibrating on each occasion that the power is lost to the system. Alternatively an uninterruptible power supply will need to be invested in. Satsio is fitted with 16-bit absolute optical encoders as standard, which in addition to providing far more accurate positioning sensing, also requires no manual action after a power interruption to read the absolute antenna position. A tracking system that does not receive regular updates over the internet will need to have its database manually updated when new satellites come into service. The use of NORAD tracking and regularly downloading the ephemeris data will ensure that if new satellites need to be accessed no manual action is required to enter its details in the tracking system database. For these, and other reasons, the Satsio system has a lower lifetime cost of ownership than competitor systems. ADDITIONAL CAPABILITY To add a monitor and control system to a satcoms installation can be extremely costly and time consuming. The Satsio controller has interfaces provided as standard to enable the connection of multiple devices and

systems. The web interface can then be customised to list the names of the devices being monitored and controlled. To access the lower cost space segment on inclined orbit satellites is often impossible for small antenna tracking systems as the power of the beacon is too small. Using NORAD tracking, Satsio can accurately point at inclined orbit satellites without needing to receive a beacon signal. Small antennas can therefore be used to access these space segment that are up to 70% lower cost than standard space segment.

Taking into account the full system cost, Satsio offers significantly more functionality, accurately and reliability for a similar capital investment to that required for one of the simpler, lower performance systems on the market. Satsio’s lifetime cost of ownership also represents a significant saving. And it offers a range of additional capability at no extra cost.

This guide has illustrated that when selecting a small antenna tracking system there are a number of areas that need to be considered (including those above), and given some information on what the options are. To keep the cost low, traditional small antenna tracking systems have had to compromise on their design in many of these areas. As a result, they do not always accurately sense the antenna position, optimnise their pointing, nor accurately position their polarization. They also require manual adjustment and offset entry, and local presence for monitor and control. By contrast, S3 Satcom has focussed on developing a small antenna tracking system that addressed all these compromises within the typical budget for such a system. The S3 Satcom Satsio is supplied with 16- bit absolute optical encoders as standard,

at a cost suitable for a small antenna tracking systems. Satsio therefore has the highest level of position sensing precision of any small antenna tracking system on the market, and reads the position of the antenna even after a power loss. When the Satsio system downloads information on a satellite’s position, even a new one just in service, it can automatically control the antenna to precisely and accurately point at that satellite without the need for any manual adjustments in azimuth or elevation. The Satsio system provides two methods for more accurately aligning small antennas—P-Step tracking and NORAD tracking—ensuring that optimal positioning and smoother tracking is achieved at all times. As standard, the Satsio system offers far more monitor and control functionality and capability to external systems and devices than any other small antenna controller in the market. It also supports a

fully feature protocol for integrating with external monitor and control systems. Taking into account the full system cost, Satsio offers significantly more functionality, accurately and reliability for a similar capital investment to that required for one of the simpler, lower performance systems on the market. Satsio’s lifetime cost of ownership also represents a significant saving. And it offers a range of additional capability at no extra cost. In conclusion, the compromises traditionally made by suppliers of small antenna tracking systems to keep the price low are now no longer necessary with the S3 Satcom Satsio system. Satsio provides the most accurate, reliable and easy to use small antenna tracking in the market, at great value for money.


Summary and conclusions

ACCURATE SENSING

ACCURATE ALIGNMENT

OPTIMAL POINTING

AUTO POLARISATION

WEB CLIENT

VALUE FOR MONEY

EASY TO INSTALL

EASY SYSTEMS INTEGRATION

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S3 Satcom Guide to Small Antenna Tracking Systems · presence for monitor and control. Small antenna tracking systems have been on the market for years. They are installed ... the