Xref: utzoo rec.ham-radio:18187 sci.electronics:10401 Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!sun!news From: news@sun.Eng.Sun.COM (news) Newsgroups: rec.ham-radio,sci.electronics Subject: Re: How does one build LOG AMPS (>60dB dynamic range) Summary: Use Plessey SL521 et al. Message-ID: <132426@sun.Eng.Sun.COM> Date: 2 Mar 90 08:39:39 GMT References: <596@massey.ac.nz> <13547@watcgl.waterloo.edu> <321@fe2o3.UUCP> Organization: Sun Microsystems, Inc. - Mtn View, CA Lines: 38 Reply-To: poynton@sun.com (Charles A. Poynton) Followup-To: Organization: Sun Microsystems, Inc., Mountain View, Calif., U.S.A. From: poynton@vector.Sun.COM (Charles A. Poynton) Path: vector!poynton Giovanni Moretti asks about a log amplifier over 60 dB at 10.7 MHz for a spectrum analyser. John Whitmore suggests the classic National Semi appnotes that exploit the logarithmic I/V relationship in a diode. John Wieczorek suggests an ICL8048; this part uses the same approach. Both of these approaches are appropriate if the logarithm of a low frequency signal, perhaps up to 10 kHz, is required. However the problem in a spectrum analyser is to get such a wide dynamic range through the IF amplifiers unscathed; IF amplifiers are just not capable of 60 dB, so the log operation must be performed at IF frequencies, not after detection. As Michael Katzmann suggests, Plessey is the place to look. They have a series of parts starting (SL521, 523, 1521, 1522, 1523) that are specifically designed as logarithmic IF amplifiers (for radar, in fact). In October 1980 these were documented in Radar and Radio Communications IC Handbook, but they're not in the March 1987 Radio Telecoms IC Handbook and I don't have the latest books. Plessey (NZ) Ltd., Auckland 8, Tel. 8364189. C. ----- Charles A. Poynton Sun Microsystems Inc. vox 415-336-7846 2550 Garcia Avenue, MS 21-10 fax 415-969-9131 Mountain View, CA 94043 U.S.A. "The most probable consequence of high tech jingoism is that it will keep the best of future technology out." -- The Economist, July 1, 1989, p. 19. -----