STL Radio Link Transmitters

STL Studio Transmitter Link
FM Radio Equipment

Studio Transmitters Microwave Links

Our STL Link Transmitter transports Cristal and Clean,
Quality audio signals from Studios
to Transmitter Sites several miles away.

Immediate delivery.

Designed to transport audio and video signals from the studio to transmission sites – maintaining high quality.

A studio link transmitter, studio transmitter link, or STL is a special type of equipment used in broadcasting industry.


This transmitter and its companion the receiver are the core of a high quality, synthesised studio-to-transmitter link (STL), to be used for broadcast repeaters in conjunction with any standard FM or AM transmitter.
They are an evolution of the previously established STL series, whose main circuitry is still extensively used here with a new controller, user interface and software, and more advanced oscillators in a compatible 2u 19" case.
These allow the reception of mono or stereo signals and its retransmission without using any additional stereo-coder on the receiving end; in both cases, the LF output signal from the receiver must be sent to the stereo input (linear or not pre-emphasised) of the local FM rebroadcast transmitter.

The STL is built for several different frequency slots, from the VHF to the SHF range.
Two main models are built: one for the 200-960 MHz range, and the other for the 1300-2500 MHz one.

While the exterior cabinet, the controls, the basic circuitry and the performances are the same, some internal components vary or are specifically tuned as required to cover this wide frequency band.
Usually, these components are: the local oscillator, the power amplifier and the input/output filters.

The factory adjusted frequency slots are 10 to 50 MHz wide and must be specified in the order.
In the preset sub-range, the frequency and power of the transmitter may be freely changed on the site.
The receiver may require some more adjustment for wider frequency displacement: in fact, the adoption of narrow, low loss input filters permitted to achieve the best possible rejection of interfering signals in the band at the expense of some frequency agility.
So, nearly 8-10MHz may be used without any retouching, but wider variation up to 50-60MHz will require retuning of the input filter.

Being the apparatuses completely digitally controlled, they are extensively programmable on site via the front panel, or remotely, in every respect.
The alphanumeric display permits easy and accurate metering, adjustment and continuous monitoring of modulation levels, power, operation and internal parameters. All this information is externally available via the same RS232 I/O port, which may be used to remotely control the transmitter.

In addition to the serial I/O, some signals and controls are available on a parallel I/O socket for easy interfacing with other analog controllers or supervisory systems.

A powerful 3-level password management permits a very high degree of security and privacy as may be required in different situations.

The LF input and output levels are precisely adjustable over a broad range, by means of 0.5dB stepwise variable attenuators.
The transmitter has also an auxiliary input, specifically designed for RDS and SCA encoders.
A modulation monitor output permits to control other transmitters or STL's with the same internally processed high-quality MPX signal.
Furthermore, the system is optimised to be compatible with external digital companding encoder/decoders and to provide RDS and SCA signals, with almost no attenuation.

Optional top-quality stereo encoder/decoder boards may be factory installed on the transmitter/ receiver or field retrofitted with minimum required technical skill.
The powerful internal software and monitoring functions recognise their presence and enable the functions.
A universal switch-mode power supply permits operation in the extended 95-250 V ac range with no intervention, and a 24 V back-up battery input is also provided.


These radio links were specifically designed to comply with the latest international standards and the requirements of advanced broadcasters, meeting tighter specifications than usually required, at an affordable cost.

Great care was spent into producing a Hi-Fi-quality modulated signal, with low residual noise and distortion. The RF signal is also free from spurious and harmonic components to a higher degree than required by CCIR, European, USA and most other national standards.


TK-STL-T1-10 Link Transmitter Band 170 - 490MHz (band max ±10MHz), 10W
TK-STL-T3-10 Link Transmitter Band 820 - 960MHz (band max ±10MHz), 10W
TK-STL-T1-20 Link Transmitter Band 170 - 490MHz (band max ±10MHz), 20W
TK-STL-T3-20 Link Transmitter Band 820 - 960MHz (band max ±10MHz), 20W
TK-STL-T5-5 Link Transmitter Band 1.4 - 2.5 GHz (banda max ±5MHz), 5W

STL Studio Transmitter Link Description

The RF signal is also free from spurious and harmonic components to a degree greater than that required by CCIR, Europe, USA, UE and most other national standards.

Maximum attention has been put into producing a modulated signal of High Fidelity and quality, with a high noise signal ratio and a very low distortion.

The TK-STL-TX transmitter and its TK-STL-RX receiver are the basis of a high quality synthesized link (STL), which is used to transport the signal from the studio to the radio transmitter or for repeaters with FM or AM modulation.

They allow reception of mono or stereo signal and its retransmission, without using any additional stereo encoder at the receiving end: in both cases, the LF output signal of the receiver can be connected directly to the MPX input of the transmitter or the local FM relay .

The STL is built for several frequency bands in the SHF range.

These radio links were designed to meet modern international standards and the requirements of existing broadcasters, complying with strict specifications at an affordable cost.

Since they are digitally controlled, they can be programmed on the radio station either from the front panel or remotely.

The alphanumeric display allows you to measure, adjust and monitor modulation levels, power and operating parameters.

All this information is available externally through the RS232.

The Low Frequency Audio input and output levels are precisely adjustable over a wide range by means of variable attenuators.

The transmitter has an auxiliary input for RDS and SCA encoders.

A modulation monitor output allows other transmitters or STLs to be fed with the same high quality MPX signal processed internally. In addition, the system is compatible with external digital encoders / decoders and to provide RDS and SCA signals without attenuation.

A universal switched power supply allows operation in the extended range of 95-250 VAC without intervention, and a 24V backup battery input is also provided.

STL Studio Transmitter Link Highlights

  • Synthesized from 48 to 900 MHz and from 1.2 to 2.7 GHz (/ 2G models).
    The transmitted and received frequencies can be easily set via the front panel display. Changing frequency is very simple and easy, thanks to frequency synthesis with 10 kHz steps, and to the simplified calibration of the input filter.
  • It is possible to vary the output level of the demodulated signal from –12dBu to + 12dBu with 0.1 dB steps and a 0.03 dB precision; the received signal level can be measured on a dBm scale (as on a spectrum analyzer) on which the squelch intervention threshold can be set.
  • Excellent stereo separation. A built-in group delay and amplitude pre-corrector guarantees a very low linear distortion and a great stereo separation in the whole 15kHz band.
  • Suitable for digital audio. The subsonic over-modulation and the low frequency phase distortion are controlled by a feedback circuit in order to exalt the audio quality of the latest digital systems.
  • Low noise. The excellent signal to noise ratio either in mono or in stereo assures the perfect use of this STL in multi-hop networks without decreasing the audio quality.
  • High sensitivity. Using ultra low noise amplifiers, selective filters and a powerful demodulation circuit, the obtained receivers sensitivity is very high, thus allowing longer link distances with a reduced antenna investment.
  • Great RF immunity allows to operate in the most hostile RF environments.
  • High adjacent channel rejection, obtained thanks to the excellent mechanical shielding and the precision of RF filtering.
  • High frequency stability with the internal temperature compensated crystal reference.
  • Simple and clear menus on a LCD graphic display allow to control all the main functions of the receiver and to precisely measure main parameters such as frequency deviation, MPX pilot tone deviation, the received signal level and squelch level.
  • Full metering: complete diagnostic and measurement of all the main parameters is available using front panel LCD display.
  • Full remote control is available as an option.
  • Provided with a battery to ensure continued functioning even in the absence of a power supply. An alarm output for remote control is also provided. VDC power supply option is available for battery or solar panel operations.
  • Meets or exceeds all FCC and CCIR requirements.
  • Components of the best brands and the newest and well-proven technologies have been employed to grant continued functioning of the receiver, high selectivity and immunity to adjacent signals and a higher audio quality.
  • The exclusive system of module removal for easy maintenance and / or internal inspection without removing panels, complete a unit suitable for all requirements.


Frequency Range 200~960 MHz -20MHz sub-band
Type of Modulation FM Class F3
VCO Tuning 25 MHz
Frequency Stability +/- 2,5ppm (Bettr 0n request)
Synthesizer Step 25KHz
Power Output 10 Watts
Spurious Emission < -80 dB or better
Harmonic Emission < -65 dB (-80 dB on request)
Stereo Separation > 55 dB @ 1 KHz
Distorsion < 0.2% (TYP 00.8 %) @ 1KHz)
Base Band 30 Hz - 60 KHz within 0.15 dB
Unweighted S/N Ratio > 74 dB rms at 30 Hz ~ 20 KHz
Enphasis 50 or 75 us selectable
RF Connectors N-F 50 ohm
Input Base Band Imp. 2 Kohm
Input Mono Impedence 600 Ohm
Cooling Forced air
OP. Temperature Range 0 ÷ +45°C
Maximum Umidity 90%
AC Supply 100 ÷ 240 Volt; 47 ÷ 63 Hz
Dimension 1 Units Rack 19” 44 cm Depth
Weight 6.5 Kg

Recommended products