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Published January 22, 2007
From: Alessandro Chianetta, STM
I am not sure how easy these words are, since it is not an easy concept. DCM is used in OFDM-UWB (Orthogonal Frequency Division Multiplexing) (Ultra-wideband) systems. It allows mapping the same databits into different constellation points from different constellation diagrams. The function associates two code data elements and transforms those elements into a format for transmission on two separate signal tones.
From: Richard Mayo, ATRAD P/L
VHF circulator/isolators have been around for quite a while. They are generally called "Gyrators" and require lumped element tuning structures at each port for the given frequency band. Try contacting one or more of the major ferrite isolator companies listed in our buyer's guide with your specific requirements. It may have to be a custom design.
From: Henderson Neves de Lima, TDCC
It should be possible to heat some other liquid besides water in a heat exchanger. However, I am not aware of any system that does so. The organization that specializes in microwave heating and industrial processing is the International Microwave Power Institute (IMPI). They can be contacted at www.impi.org and may be able to help you.
From: Maurizio Brignoli, Telewire Italy
Although simulation software is better than ever and keeps improving, the structures or elements that are actually used in the prototype construction are not perfect, particularly for high Q circuits where small differences in available Q will have a significant effect. This is one of the reasons that Microwave Journal requires measured data in the papers that we publish.
From: Johana Yan
The use of 50 ohms as the industry standard for characteristic impedance is a compromise between 44 ohms, which is the Zo for the highest power capability in coaxial air lines, and 93 ohms, which provides the lowest attenuation in coaxial air lines. For a teflon-filled line the lowest attenuation is at 64 ohms. There are a number of variations to these figures due to other factors; however, 50 ohms was established many years ago and it has remained the standard.
From: Mustafa Karakoc, Kocaeli University
2.) In downlink at the mobile user, what is the Eb/NoIo threshold value of data for the user with different data bit rates? For example, there is a user with a data bit rate request of 9.6 kb/s (basic rate or R). It is clear that the user is not only receiving its signal, but multipath signals related to the desired signal are also getting another user's signals. After downlink analysis, the signal's BER level has to compare with reference predefined threshold level. For example, S=Eb / (No+Io) level is 5.5 dB for 9.6 kb/s 3.6 dB for 38.4 kb/s. Is there more predefined threshold levels for different data bit rates? For example, what are the data bit rates for 76.8 kb/s or 28.8 kb/s?
Your question is a communications systems question that is outside my area of expertise, so I cannot answer you directly. However, I can recommend several texts, which may be helpful:
Digital Techniques for Wideband Receivers, J. Tsui, Artech House Inc., 2001, ISBN#1-58053-299-3;
Advanced Techniques for Digital Receivers, P. Page, Artech House Inc., 2000, ISBN#1-58053-053-2;
Harlan Howe, Jr. received his BS degree in optics from the University of Rochester in 1957. He has been actively engaged in the microwave industry for 48 years, first as a design engineer and then as an engineering manager. In 1990 he became the publisher/editor of Microwave Journal. He retired as publisher in 2001, but remains the editor. He is a Life Fellow of IEEE, past president of MTT-S and the recipient of an IEEE Third Millennium Medal in 2000 and the MTT-S Distinguished Service Award in 2005.
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