Lec06mixers - ECE 488 RF Circuits and Systems Spring 2008...

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1 1 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: Mixers ECE 488 RF Circuits and Systems Spring 2008 Lecture 6 2009/1/30 2 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: Announcements Labs start next Monday. Lecture number error in bottom right corner of handouts…it should be 6 (not 7). 3 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: We are almost to the point where we have enough building blocks to build a radio receiver! How about the following system? Transmit and receive “audio” frequencies Some Radio Ideas 4 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: Our simple system will not work because Efficient antennas would be huge! (How huge?) We could only have one radio station (why?) Noise is not dealt with (i.e., to minimize it) Not enough power to drive speaker Conclusion: Audio RF frequencies not practical. Will an “Audio Frequency” Radio Work? miles! 186 km 300 m 310 kHz 1 m/s 10 3 Wavelength 5 8 = = = × = = = f c λ 5 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: 1880’s: Hertz demonstrated Propagating E and M wave Using a high voltage over a gap to create sparks Spark created lots of high frequencies Transmits a few kW Sufficient to be detected at a remote site. Morse code (on-off signal)…primitive modulation Spark gaps used until ~1920! Some Radio History – Spark Gaps 6 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: Simple Transmitters and Receivers Generator and key Diode detector receiver Signal present, or no signal present Some Radio History – Detectors
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2 7 Swartz 07/1/31 ECE 488 – RF Circuits and Systems – Spring 2009 Lecture 6: Rotating generators with lots of poles to generate frequencies up to 50 or 60 kHz WWV still uses this frequency for broadcasting universal time codes because propagation time is not affected by the ionosphere, so time to get to any location is relatively constant.
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This note was uploaded on 07/09/2009 for the course ECE 4880 taught by Professor Swartz during the Spring '06 term at Cornell University (Engineering School).

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Lec06mixers - ECE 488 RF Circuits and Systems Spring 2008...

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