Prof. Dr. Ing. Habil Ulrich L. Rohde of https://www.uoradea.ro/Galeria+de+onoare

In the age of wideband modulation capabilities, our “good old” signal generators maybe nice and low noise, but unable to generate the needed modern signals. On the other had they are a good starting topic to explain the circuitry of analog signal generators, even their complexity and how and why modern signal generators evolved. This also needs an introduction to frequency synthesis. In this lecture, Introduction to Modern Signal Generation; from Analog to Digital: Needs, Advantages, Disadvantages and "Solutions" will be disucssed for modern Radios applications.
The traditional communication essentially took place from point to point and starting with AM modulation, for broadcast later with FM modulation, evolved to single side band suppressed carrier modulation (SSB). For the most reliable communication, MORSE code was invented and in many ways is still used and actually the forerunner of digital modulation. 
The transmission of information from a fixed station to a mobile is considerably influenced by the characteristics of the radio channel. The RF signal arrives at the receiving antenna not only on the direct path but is normally reflected by natural and artificial obstacles in its way. Consequently the signal arrives at the receiver several times in the form of echoes which are superimposed on the direct signal. This superposition may be an advantage as the energy received in this case is greater than in single-path reception. This feature is made use of in the DAB single-frequency network. However, this characteristic may be a disadvantage when the different waves cancel each other under unfavorable phase conditions. In conventional car radio reception this effect is known as fading. It is particularly annoying when the vehicle stops in an area where the field strength is reduced because of fading (for example, at traffic lights). Additional difficulties arise when digital signals are transmitted. If strong echo signals (compared to the directly received signal) arrive at the receiver with a delay in the order of a symbol period or more, time-adjacent symbols interfere with each other. In addition, the receive frequency may be falsified at high vehicle speeds because of the Doppler effect so that the receiver may have problems to estimate the instantaneous phase in the case of angle-modulated carriers. Both effects lead to a high symbol error rate even if the field strength is sufficiently high. Radio broadcasting systems using conventional frequency modulation are hardly affected by these interfering effects. If an analog system is replaced by a digital one which is expected to offer advantages over the previous system, it has to be ensured that these advantages--for example, better AF S/N and the possibility to offer supplementary services to the subscriber--are not at the expense of reception in hilly terrain or at high vehicle speeds because of extreme fading.

For this reason a modulation method combined with suitable error protection has to be found for mobile reception in a typical radio channel, which is immune to fading, echo and Doppler effects. With a view to this, more detailed information on the radio channel is required.

Biography:

Ulrich L. Rohde, Dr.Ing. habil., is a Professor of RF and Microwave at the University of Cottbus, Germany, Chairman of Synergy Microwave Corp. NJ, USA, Professor at Oradea University, Romania, honorary professor at IIT Delhi, India; President of Communications Consulting Corporation, FL, USA, and a partner in Rohde & Schwarz, Munich, Germany. Dr. Rohde is past member of the board of directors and a former executive vice president of Ansoft Corporation, now it is Ansys. He is an IEEE life Fellow, published over 300 scientific papers in professional journals and conferences, co-authored of 12 technical books and book chapters, over 3 dozens patents into his credits and recipients of more than dozen scientific and IEEE society awards. In 2006, Dr. Rohde was honored as Microwave Legend by Microwave & RF Magazine; the selection was based on global voting. In 2009, Dr. Rohde was selected in the list of Divine Innovators of November 2011, Microwave Journal. Based on Dr. Rohde’s 5-decade of scientific creativity and pioneer contributions in the field of microwave and antenna, IEEE has established 2 awards on his name “IEEE Ulrich L. Rohde Innovative Conference Paper Awards on Antenna Measurements and Applications” and IEEE Ulrich L. Rohde Innovative Conference Paper Awards on Computational Techniques in Electromagnetics”. His hobbies are sailing, U.S. Merchant Marine Officer, Master of Steam or Motor Vessels, photography and ham radio (Dj2LR and N1UL).

Email:

Address:Oradea University, Information Technology and Electrical Department, Oradea, Romania