Global player in communications field,
is well recognized as one of the
broadcast world innovator firms of all times.
Today, after the recent acquisition of Electrosys by Elenos under Itelco Broadcast name, Elenos & Itelco group aim to the integration of superior engineering and technological capabilities by providing, together, over 90 years of broadcasting expertise worldwide.
The Broadcasting &
High Reference Standards
ITELCO Broadcast business lines, i.e. supply of radio television transmitters, design for
scientific and medical applications, design of “turn-key” and/or custom projects, set
full attention and committment in offering very high level technologies, range top
performances, quality and exibility.
The adoption of leading edge technologies as well as solid and attractive design,
represent by now the distinguishing feature identifying ITELCO Broadcast products.
The high reference standards relating to all product lines, with possibility
of customized solutions, make the product and the relevant service unique for complying
whatever requirement type.
Our committment is to continue proposing, to all branches in which we operate, those
excellency levels which will represent tomorrows technological standards.
Angine, osteoporosis and cancer,
might be cured also with ITELCO’s technology
The European Spallation Source (ESS) will be a new generation of protons linear accellerator providing neutron beams up to 30 times brighter than any current neutron source.
This new Pan European laboratory will help to discover and develop new materials with applications in manufacturing, pharmaceutical drugs, aerospace, engines, plastics, energy, telecommunications, transportation, information technology and biotechnology.
FREIA project at Uppsala University performs testing for ESS hardware elements.
In last July 2015 Itelco installed the 400 kW pulsed tetrode amplifier representing the RF power source for the Spoke Cavity (superconducting).
Today Itelco’s scientific department is leader on the market: in first line for the ESS future upgrades and also involved in projects with CERN and Elettra – Sincrotrone Trieste (Italy).
Higher safety with Itelco’s FM transmitters.
Transmitters installation and commissioning for
the Italian Highway Advisory Radio are still in progress.
DOHERTY POWER AMPLIFIER REAL BROADBAND, TODAY IS NOT A DREAM!!
Doherty Power Amplifier (DPA): dividi et impera.
A contemporary telecommunication equipment must have features, in terms of signal linearity, high power and also top efficiency, such to meet energy saving requirements.
Transistor amplification with latest MOSFET generation allows valuable efficiency levels (above all considering their evolution in these last years), raised with the introduction of liquid cooling in the past 20 years.
Nowadays, with Doherty technology application in amplifier stages of television transmitters, a new challenge was launched.
William Doherty was an engineer of Bell Telephone Laboratories who, in 1936, designed a circuit using two class B tubes that in parallel were operating as a linear amplifier for AM radio transmitters.
The previous version was using class B tubes in “push-pull” configuration with a transformer combining the tubes’ output signal. The push-pull system was functional and powerful but not energy efficient.
A DPA uses two amplifiers: the polarized MAIN to operate, for instance, in class AB; and the polarized PEAK to operate, for instance, in class C. The input signal is divided in equal parts by means of a power hybrid with a 90° phase shift.
The signals, amplified separately, are then re-combined through a power combiner that re-alligns them in phase.
In presence of high level input signal, both amplifiers are active: the MAIN assigned for amplifying the low part of the frequency modulation and the PEAK entering into operation in case of high levels of frequency modulation, over preset thresholds.
Time trend of a multicarrier signal
In presence of low level signals, the PEAK amplifier switches off (our class C example): only the MAIN stays active (class AB). In this phase, the MAIN operates, alone, in high gain and efficiency condition.
The system is very efficient in presence of signals having a high PAR (Peak/Average Ratio); therefore characterized by a high ratio between reachable peak power and medium power of the signal to be spread.
The DPA introduction in AM equipment increased the conversion efficiency from 30 to ver 60%, representing the standard of the AM “tube” transmitters manufactured by Western Electric, Continental, Marconi and by RCA (until the 70s).
The first application of this technology was a 500kW AM transmitter manufactured by Western Electric Company, installed in 1938 for WHAS, a radio station nearby Louisville in Kentucky.
The AM signals have a low PAR (Peak to Average) ratio and, therefore, very little changed till the 2000s.
Only with the arrival of digital and mobile telephony, the William Doherty technology had a new youth.
In fact, a peculiarity of UMTS/CMDA telephone signals, and in general of OFDM (WiMAX, LTE) modulation systems, is the high Peak/Average ratio (going from 4dB in analog to over 8db in DVB-T).
Moreover, many thousands small mobile telephony stations made necessary the research of technologies allowing savings in terms of power consumption or of heat dissipation (with DPA, mobile telephony operators’ savings increase up to 15% on network management costs).
When Doherty designed his amplification system, technologies were obviously very different.
By examining the “pure” DPA, it can be seen that the output linearity is lower compared to the one of a class AB amplifier and, therefore, producing a higher distortion.
However, we know that operating the power amplifiers in non linear zone, these gain in efficiency. Here helps the modern progress in digital predistortion, in linearity techniques, in design and in new MOSFETS introduced on the market by the manufacturers of semiconductors.
Nowadays, out of the most popular linearity techniques: mixed techniques, Feedback, Feedforward, Predistortion, only this lattest is largely used in broadcast.
Notwithstanding the modern evolutions in terms of design and technology, broadcasting approached Doherty since a couple of years only. This is due mainly to the difficulty in reaching 35dB MER without retreating high efficiency levels in precorrection and to the Doherty being a narrow band system (two or three channels). This was a growth limiting factor in a market where frequency agile amplifiers are requested.
Recently progresses were achieved in design of Doherty technology UHF pallets. It was achieved to split the UHF band in 3 parts, i.e. 3 different pallets design (generally naming them as “broadband”).
To reach the real broadband pallet in full-doherty technology a miracle is to occur…. Or maybe not.
In 2016 Itelco again moved ahead towards the very next future.
The REAL efficiency, measured at mains input/Pout up to 42% and over, became a fact and again will represent the comparison stone for the reference market.
Prof. Eugenio Fumi