AM Single Frequency Network
Single frequency networks (SFN) in the medium wave broadcast band were introduced in Germany in the late 20ies and early 30ies. They were developed by C. Lorenz A.G. So a short presentation of Lorenz transmitter development is given. A complicated problem then was the synchronization of these SFN. Therefore pilot tones of about 2 KHz were used and transmitted via telephone trunk lines. A frequency multiplication was necessary at the transmitter's side. Some solutions used a technique called today PLL. Between the SFN transmitters is a zone of heavy interference, where nonlinear distortion of the received AM signal occurs. Nowadays SFN's use digital modulations, and interference no longer plays a major role. Some principles of single and multi carrier radio systems are presented. In former days jamming transmissions on AM occurred. Optimal AM jammers use DSB modulation. In WW2 a jamming with intelligible text message was used. The modulation usable was SSB.
Original text in RM.org
German text .pdf file (97.2 KB) for automatic translation click here.