FM STL Link Microwave Aural Transmitter 170-490MHz-10W

STL Link Transmitter

Our STL Transmitter Link, transmits Cristal and Clean High Quality Audio Sound From Studio to Transmitter Site-B170-490MHz-10W-Worldwide Immediate delivery

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


This transmitter and its companion 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 previous extablished series stl 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. They allow the reception of mono or stereo signal 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 VHF to the SHF range. Two main models are built: one for the 200÷960 MHz and the other for the 1300÷2500 MHz range. 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 field. 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 on field programmable by 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 these information are externally available on the same RS232 I/O port that 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 others analog controllers or supervisory systems. A powerful 3-levels 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 provided too.


Like the Transmitter, the Receiver front panel accommodates the single control knob, the display, four leds for immediate status control and a single output connector for IF monitoring.

Here too regular operation is signallized by green leds: "PLL Lock" and "Field". This latter is a bi- stable and lights in yellow when RF field is too low or absent. As in the Transmitter red leds signals improper operation. The first one, "Modulation", is activated by low or absent modulation; the last one is the general "Alarm" led.

The Receiver I/O connectors on the rear panel are:

  • The mains supply IEC320-type outlet, which incorporates the mains switch and the fuses. An additional earth screw for system earthing and a 24V-battery backup socket pair. In alternative the mains outlet with fuse-holder and the mains switch may be separate components
  • The RF antenna connector, N-type
  • The main composite signal output (Mpx+, Mpx-) on two BNC-type connectors in antiphase, permitting direct drive of two separate transmitters or one in balanced mode.
  • A buffered LF monitor, BNC-type connector that may be internally connected as an additional composite or wide-band or mono signal output.
  • The filtered/de-emphasised mono signal on a balanced male XLR-type connector.
  • The L & R audio channels output sockets on balanced XLR-type connectors (only with internal Stereo Decoder option).
  • A RS232 Dsub9 female remote serial control port, inverted wired.
  • A parallel control port, Dsub9 male type


Factory preset frequency ranges 215÷245Mhz 240÷270Mhz

300÷340 Mhz 340÷380 Mhz

400÷440 Mhz 430÷470 Mhz

810÷850 Mhz 850÷890 Mhz

890÷930 Mhz 930÷960 Mhz

1350÷1375 Mhz 1370÷1390 Mhz

1429÷1433Mhz 1510÷1530Mhz

1660÷1670Mhz 2367.5÷2372.5Mhz

2440÷2.450Mhz 2468.1÷2483.3Mhz
Modulation FM, 75 kHz peak dev.

180kF3E mono

256kF3E stereo
Synthesis step 10kHz (215÷960 Mhz)

25kHz (1.3÷2.5Ghz)
Composite Mpx output response 15 Hz ÷ 67 kHz +0.1/-0.5dB

<-6 dB @ 100 kHz

<-20 dB @ 125 kHz
Monitor output wide-band response 15 Hz ÷ 100 kHz +0.1/-1.5dB

-3 dB typ. @ 125 kHz

-6 dB typ. @ 160 kHz
Mono/stereo decoded response 30 Hz ÷ 15 kHz ±0.2dB
S/N ratio (30÷20000Hz rms) >75 dB, 80 typ. mono

>72 dB, 76 typ. stereo
Modulation distortion(100%dev.)
@1kHz/ mono ≤0.1% 0.03% typ.

stereo,1ch ≤0.30% 0.20%typ.
@ 30÷7500 Hz mono ≤0.25% 0.12%typ.

stereo,1ch ≤0.30% 0.20%typ.
Stereo crosstalk(typical) >50dB(400÷10000Hz)

>40 dB (100÷15000 Hz)
I/Olines Alarm, RF/LFdisable, Low RF field

remote control/lock

RS232 for monitoring and control
Mains requirements 110 - 240 V~ 50/60 Hz

24 V=
Operating temperature range 0÷35° C recomm.

-10÷45 °C max


Noise figure ≤9dB
Image frequency rejection ≥60dB 70typ.
Dynamic selectivity >+10dBtyp@δF=300kHz

>+35dB typ @ δF=500 kHz

>+45dB typ @ δF=1.0 MHz
AM suppression >45dB
Usable input level -90÷-10dBm

Sensitivity (typical) Sin=-90dBm(7μV) mono

(S/N=60dB) Sin=-70dBm(70μV)stereo
IF monitor output 10.7MHz/0dBm
Wide-band demodulated output response 15 Hz ÷ 120 kHz +0.1/-3dB
Wide-band demodulated output level +6dBm
MPX output level -1.5 ÷ +12 dBm, 0.5dB/step
Mpx output response 15 Hz ÷ 67 kHz +0.1/-0.5dB
mono or stereo decoded response 30 Hz ÷ 15 kHz ±0.1dB
Out-of-band mono or stereo audio response >50 dB @ F≥19 kHz
De-emphasis time constant 0/50/75μs±2%
S/Nratio(30÷20000Hz.rms) >72 dB, 76 typ. Mono

>70 dB, 73 typ. Stereo
Modulation distortion @1kHz/100%dev. mono ≤0.1% 0.03% typ.

stereo, 1ch ≤0.30% 0.20%typ.
Stereo crosstalk >50 dB(100÷5000Hz)

>45 dB (50÷15000 Hz)
I/O lines LF disable, Low RF field, Alarm, RS232 control and monitoring
Mains absorption 15Wmax@110-240V~
Battery absorption ≤0.4A@24V=
Dimensions, without handles 19" 2 un. std. Rack


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