The Difference Between Test Loop Translators and Satellite Link Simulators

John Dunstan - Atlantic Microwave

Oct 10, 2019

Teleports have a great deal of built-in test equipment, yet for mobile earth stations, which due to their size, do not have room for built in test equipment; Test Loop Translators (TLTs) and Satellite Simulator Systems are valuable tools to ensure smooth operations. Both solutions simulate a satellite link for test and alignment of systems, and whilst the applications for TLT’s and Satellite Simulators may be similar, there are some fundamental differences that are important to understand before deciding which is best for your set-up.

The Importance of Satcom Testing

As consumer demand for high quality coverage increases, the pressure is on to get ground stations and satellite news gathering (SNG) vans set up quickly, and crucially; operating seamlessly. Operators place a great deal of importance on ensuring the right products are in place, however testing the performance of an entire ground station can often be considered as being too time intensive and this leads to ground stations going live, without that important step.

TLT’s and Satellite Simulators are an ideal solution in evaluating the performance of satellite earth systems, making testing simple, quick and cost-effective. 

Both products are designed to test the entire operation of a ground station, as opposed to just one section, by simulating a satellite link. They both convert frequencies from an uplink to a downlink, however they differ in how they operate, and so it is important to understand the difference to determine which is the right solution for your setup.

Test Loop Translators – the cabled solution

The fundamental difference between the two technologies comes down to the connection. TLTs connect via a coaxial cable, as opposed to via an antenna. Meaning the power produced in the uplink can be precisely measured, enabling extremely controlled tests, to ensure a high level of accuracy.

Using a TLT and measuring via cables, presents a clean signal, however, noise generators are often used in conjunction with TLTs; applying signal noise to provide an accurate representation of a satellite signal.

For those earth stations operating on two different frequency bands, dual test loop translators make it possible to test both simultaneously using the same piece of kit.

TLTs are quick to setup and deploy in most cases, allowing you to test your ground station in very little time. The only exception to that is in the case of ground systems where the antenna is integrated. In these cases, it would be better to use a Satellite Simulator as disconnecting the antenna can be problematic or in some cases not possible.

Satellite Simulator Systems – the cableless approach

A Satellite Simulator System is a cableless RF test solution, using an aerial to connect to the earth station. This enables portable loop-back RF testing for optimum equipment location. Satellite simulators can be either depot-based or portable, ideal for testing and calibration of news gathering and outside broadcast systems off-satellite.

Simulator systems are designed with integrated and appropriately polarised gain horn antennas.  It receives at the transmit (Tx) frequency and transmits at the receive (Rx) frequency, thereby completing the loop-back without satellite involvement.

Simulators provide a more realistic representation of signal noise, as the test signal is being sent in the same way as you would a live signal. In some applications, it may be more important to have a clean signal for testing, but in others a realistic representation could be key.

With Satellite Simulators you don’t need to break the connection between the earth station and the antenna. Add to that the ease of use, you can see why they are especially ideal for testing in the field. Setup is quick and easy. Essentially it is a question of putting it in place, ensuring it aligns accurately, then performing the test.

When to use a TLT or Satellite Simulator?

TLT’s and Satellite Simulators are used to test ground systems, verifying a perceived hardware fault under controlled conditions, before embarking on a costly repair process.

Test Loop Translators are generally suited to production tests as well as final pre-live tests. As the system is not yet live, there is no concern about taking it offline. It is also easier to add the connection via a coaxial cable at this stage. 

Satellite Simulators are often the chosen method in the field, where there is an emphasis on speed of testing and a need to keep the signal live during that process. This is an interesting area right now and one which only now seems to be recognised by the industry. We will likely see further innovation in the coming months to make this field testing with Satellite Simulators even simpler.

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