The Introduction to Studio Transmitter Link (STL)

Have you ever heard of studio transmitter link or STL? It is a broadcasting system often used in a digital studio built in the city. It is like a bridge between the studio and the FM broadcast transmitter, allowing the broadcast content to be transmitted from the studio to the FM broadcast transmitter, and solving the problem of the poor FM broadcast effect in the city. You may have many problems with this system. This share is going to introduce the Studio to Transmitter Link to give answers for you.


Interesting facts about studio transmitter link, Let's have a basic understanding of studio to transmitter link before our further learning.
Definition of Studio Transmitter Link

Studio transmitter link is also called studio to transmitter over IP, or studio transmitter link, or STL directly. According to the definition of Wikipedia, it refers to a studio transmitter link equipment that sends a radio station's or television station's audio and video from the broadcast studio or origination facility to a radio transmitter, television transmitter, or uplink facility in another location. This is accomplished through the use of terrestrial microwave links or by using fiber optic or other telecommunication connections to the transmitter site.


2 Types of Studio Transmitter Link

Studio transmitter links can be divided into analog studio transmitter links and digital studio transmitter links (DSTL).


  • Analog studio transmitter links are often used for large radio or television stations (radio or television stations at or above the provincial level), with strong anti-interference and anti-noise functions.
  • The digital studio transmitter link is often used for radio or television stations that need to transmit audio and video for a long distance. It has a lower signal loss and is suitable for long-distance transmission (up to 60 km or 37 miles).


Role of STL

Why do broadcast studios adopt STL? As we all know, in order to maximize the coverage of FM radio broadcast transmitters, they are usually set high on the radio transmission towers on the top of the mountain. But it is almost impossible and unreasonable to build a broadcast studio on the top of the mountain. And you know, the broadcast studio is usually in the center of the city. 


You may ask: why not set the FM radio transmitter in the studio? This is a good question. However, there are so many buildings in the city center that it will greatly reduce the coverage of the FM radio transmitter. It is far less effective than set the FM radio transmitter on the top of the mountain. 


Therefore, the STL system plays the role of a hub to transmit the audio and video signals from the studio to the FM broadcast transmitter on the mountain, and then broadcast the radio programs to various places through the FM broadcast transmitter.


In short, no matter analog STL or digital STL, they are the pieces of point-to-point broadcasting equipment that connect the studio with the FM radio transmitter.


How Does A Studio Transmitter Link Works?

The following figure is a brief working principle diagram of Studio Transmitter Link provided by FMUSER. The working principle of the STL system is briefly described in the figure:


  • Input - First, the studio inputs the audio signal of broadcast content through the stereo interface or AES / EBU interface and inputs the video signal through the ASI interface.


  • Broadcasting - After the STL transmitter receiving the audio signal and the video signal, the STL transmitter antenna will transmit these signals to the STL receiver antenna in the frequency band of 100 ~ 1000MHz.


  • Receiving - The STL receiver receives the audio signal and video signal, which will be further processed by other electronic equipment and transmitted to the FM broadcast transmitter.


Just like the principle of radio broadcasting, Studio Transmitter Link broadcasts signals in 3 steps: Input, broadcasting, and receiving as well.


Can I Have My Own Studio Transmitter Link ?

"Can I have my own STL?", we have heard this question many times. Since microwave STL systems are often expensive, many broadcast companies will choose to rent STL systems. However, it is still a large cost as time moves on. Why not buy ADSTL of FMUSER, you will find that its price is similar to that of rental. Even if you are with a limited budget, you can have your own STL system.


ADSTL digital broadcasting package from FMUSER covers the studio to transmitter link equipment for radio stations, including studio transmitter and receiver with LCD panel control system, ultra-light stainless steel Yagi antenna with high gain, RF antenna cables up to 30m, and required accessories, which can meet your various needs:


  • Save your cost - ADSTL of FMUSER can support up to 4-way stereo or digital high fidelity (AES / EBU) audio input, avoiding the increased cost of purchasing multiple STL systems. It also supports SDR technology, which allows you to upgrade the STL system through software instead of re-purchasing hardware.


  • Meet multiple frequency bands requirement - ADSTL of FMUSER not only supports 100-1000MHz frequency band but also supports up to 9GHz, which can meet the transmission requirements of various radio stations. If you need to customize the working frequency and have passed the application of the local management department, please feel free to contact us to customize the ADSTL model and frequency you need.


  • High-quality signal transmission - ADSTL of FMUSER has excellent anti-interference performance. It can transmit high fidelity HD-SDI audio and video over a long distance. Audio and video signals can be transmitted to the radio transmission tower almost without any loss.


ADSTL of FMUSER is definitely the most cost-effective Studio Transmitter Link solution for you. If you are interested in it, click here for more information. 




What kind of Antenna Does The STL System Use?


Yagi antenna is often used in STL systems, which can be used for vertical and horizontal polarization to provide good directivity. Excellent Yagi antenna usually has the characteristics of excellent radio ease of use, high gain, lightweight, high quality, low cost, and weather resistance.


What Frequency Can STL System Use ?


In the early stage, due to immature technology, the working frequency of the STL system was limited to 1 GHz; However, due to the improvement of solid-state technology and the increase of transmission capacity of broadcasting companies, the transmission range of commercial systems is as high as 90 GHz. However, not every country allows STL systems to use so many operating frequencies. The frequency bands provided by FMUSER include 100MHz-1000MHz, 433-860MHz, 2.3-2.6GHz, 4.9-6.1GHz, 5.8GHz, and 7-9GHz, which can make you not limited by the local radio management department.


Is It Legal To Use The Studio Launch Link SystemIn My Country ?


The answer is yes, studio transmitter links are legal in most countries. However, in some countries, the use of studio transmitter link equipment will be limited by the local management department. You are required to submit relevant certificates to the management department to obtain the use license.


How Do I Determine If The Studio Transmitter Link Is Licensed?


Before using or purchasing studio transmission link equipment, please ensure that you have applied to the local radio management department for the use license of the STL system. Our professional RF team will assist you in the subsequent matters of obtaining the license - from the time the equipment is issued to its completely normal and safe operation.



With the acceleration of urbanization all over the world, the STL system has become an indispensable part of broadcasting studios. As a bridge between broadcasting companies and FM radio transmitters, it avoids a series of problems such as too much signal interference, too many buildings, and height restrictions in the city, so that broadcasting companies can operate normally. 


Do you want to start your own STL system? As a professional radio station equipment supplier, FMUSER can provide you with high-quality and low-cost ADSTL studio to transmitter link equipment. If you need to buy an ADSTL system from FMUSER, please feel free to contact us.


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