Product Details

TLT- Test Loop Translators


RF and Microwave TLT- Test Loop Translator:- About, Types, Application, Design:

Test Loop Translator (TLT) is a type of radio-frequency converter, used to convert the frequency within the same band to evaluate the performance of satellite base station systems.

  • To evaluate the earth station system, instead of a satellite, the uplink signal will transmit to the TLT then TLT will convert this signal into a required downlink signal which Satellite used to send back to the earth station, through this all the earth station systems can be evaluated without having actual satellite.

As connecting to a real satellite can cause interference with other satellite users and is expensive, TLT is an important system when testing and evaluating SATCOM base station systems.

  • The prime component for a TLT- Test loop Translator is an RF Mixer, which can accept two frequencies and generate a new frequency by mixing the signal with and local oscillator signal very nearer to one of the input frequencies.

To learn more about RF and Microwave systems, we recommend you to check the following article.

To understand the TLT in a better way, we recommend understanding more about the following components, which are prime components for the construction of test loop translators.

In this RF and Microwave TLT article, we will cover,

  • What is an RF and microwave Test Loop Translator?
  • Types of RF Test Loop Translator?
  • Applications of RF and Microwave Test Loop Translator?
  • What are the specifications that need to consider in the selection of an RF Test Loop Translator?
  • RF and microwave Test Loop Translator Manufactures.

Prime features of a perfect Test Loop Translator:

The prime feature of any Test Loop Translator is to meet the frequency stability and phase noise requirements of the SATCOM industry. Following features will have an added advantage for the users in practical applications.

  • The flexible and comprehensive monitor
  • MultipleOperating Bands like S C, X, Ku, and Ka in a single system.
  • External and internal LO for reference signal with Fine-tuning steps.
  • Front panel local control for setting the parameters.
  • Full remote control option through LAN or RS232.
  • Low Phase Noise over the entire frequency of operation.
  • Dimension must meet the standard like 19” rack.
  • Gain Control option and its stability.

Design and Application

RF TLT- Test Loop Translator Design concept?

A test loop translator (TLT) is used to translate frequency between uplink and downlink signals. TLT will create a "loop-back" for testing and calibration of equipment in a satellite ground station without interface with the satellite.

  • A basic version of TLT- Test loop translator consists of a mixer with a local oscillator ( Internal or external). Advanced versions of TLT, will have the features like signal level setting, frequency band switching and other parameter controls to match various test scenarios.

TLTs generally contain a fixed local oscillator (LO) and have a negative gain (i.e., signal attenuation), in the range of  -10 to -15 dB being the most common attenuation. Most of the Test loop translators can cover one or more bands of the satellite communication like S, C, X, Ku, DBS, and Ka.

  • The design of a TLT is similar to the design of a UP/Down Converter. The prime difference is the mixer will have very close input and out-put frequency bands.

RF mixer in the TLT-test loop translator will have basically 2 input and 1 output port, one port is to feed the input RF signal ( Uplink or down like frequency signal) and the second port is the feed local oscillator signal ( Internal or External). In the third port (output port), we will get the combined or the difference of 2 input frequencies. The frequency which is required will pass through to the output of the TLT and the other frequency will get terminated/canceled inside the TLT.

Design Flow:

Step 1: Select suitable RF mixers which can convert the required band of uplink frequency to downlink frequency or vice versa.

Step 2: Select the suitable filters, attenuators, isolators to be used at different stages of the Test Loop translator, as per the block diagram.

Step 3: Select the RF synthesizer (LO) which is used to feed the LO signal to the mixer to convert the input to the output frequency.

Step 5: Line up all the components as per the block diagram of TLT, in such a way that the signal loss will be minimal as per the link budget.

Step 6: For calculating the losses in each stage of the chain, we can use dedicated design software or a simple excel file by entering the insertion loss of each component from the respective datasheet of RF components.

Step 7: Once we selected all the components as per the block, we can assemble the entire system and terminate all the open ports, and finalize it with suitable connectors for the uplink and downlink.

What is the difference between an RF up-Down-converter and a TLT-Test loop translator?

Both Test Loop Translator and Up / Down Converter are frequency converters.

In Test Loop Translator frequency conversion, usually with the same or similar input and output bandwidth, with pre-set Local Oscillator (LO), and gain. TLT is used to translate signals between uplink and downlink segments for the testing of the satellite base station systems without a satellite.

In the case of Up / Down converters, it is used to convert lower frequency to a higher frequency or high frequency to intermediate frequency (Lower frequency ). The system to convert IF to RF is called Up-converter and the system to convert RF to IF signal is called Down-converter. RF and Microwave frequency down and up-converters are used in the receiver and the transmitter chain of any RF communication system.

Applications of Test Loop Translators:

The prime application of Test Loop Translators is to test and alignment of earth station systems without having a real-time satellite link.

  • Many manufactures offer Test Loop Translators with Manual and Ethernet Control with Reversible Signal Path options, this will help the base station engineers to set up the entire system of uplink and downlink in the base station and carry out analysis, alignment, evaluate system performance and system testing without having a satellite in place (without connecting to a real satellite).

Test loop translators are primly used during equipment development, deployment, qualification, troubleshooting, and routine monitoring of the satellite base station.

Basics & Selection Feature

Main specifications need to consider in the selection of Test Loop Translators.

The important parameters to consider for a Test Loop Translator are operating frequency, Multiple Operating Bands, isolation among the bands, power output in each channel, conversion gain/loss, and noise figure.

Frequency of operation: 

Both the uplink and a downlink frequency of operation need to match with the satellite up and down like frequency bands. The Narrowband of frequency covering will help to avoid the unwanted signal passing through it. There are many manufactures offering TLT with Multiple Operating Bands options, it will be ideal for the application, as there is a chance of changing the link frequency in the later stage.

Gain (dB) / Insertion loss:

The gain / Insertion loss of a Test loop translator indicates the net increase/reduction in power level between the input and output from the TLT. Ideal to select a TLT with an option for the gain control, this feature will help to simulate the link budget at the time of initial deployment of the base stations.

Isolation between the channels:

If a TLT is designed to operate multiple uplinks and downlink frequency, it is important to check the isolation between the frequency bands. Better the isolation, better for the testing and evaluation of the base station.


Spurious are the undesired frequencies generated inside the mixer of the TLT. Need to select a TLT with the Lower spurious content output.

Power and Dynamic Range:

The power output of a test loop translator is directly related to the gain of the TLT, power output should meet the link budget of the satellite link. The dynamic range indicates the power range over which TLT is designed to operate without variation in performance.

Noise figure (NF):

Noise figure (NF) of the Test loop translator is defined as the added noise generated within the system. TLT with a lower value is better for the application.

RF connectors:

RF test loop translators are available with various connectors options like SMA, N-type, 3.92 type, etc as per the frequency of operation requirement.


Test loop translators- TLT is one of the prime required instruments for the SATCOM industry to set up, regularly monitor, and aligning of the base station instruments without a satellite in place.

Below is the list of top listed RF and Microwave Test loop translators manufacturers. If you would like to recommend any manufactures or any specific feature about any particular Test loop translator to us, feel free to contact us or register through the manufacturer registration button on the top of this page.

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