K9YC |
What is K9YC? K9YC is the amateur radio callsign assigned to Jim Brown by the Federal Communications Commission (FCC), an agency of the US government that oversees broadcasting and communications in the United States. Amateur radio as a hobby allows individuals to work expermentally with radio in many ways. To obtain a license, we must pass an examination that covers both the technical side of radio and the rules governing our use of it. Amateur radio operators (hams) are well known for providing emergency communications in emergencies -- hurricanes, tornadoes, explosions -- and in support of special events -- fund-raisng races and walkathons for various charities. Ham radio has also been an avenue for young people potentially interested in a career in many fields of radio and electronics. ARRL (originally known as the American Radio Relay League) is the national organization of hams in the United States. RAC and RSGB are the corresponding societies in Canada and the United Kingdom.
K9YC enjoys making technical presentations to ham clubs. I'll be responsible for my own travel costs around the Bay Area. I'm happy to speak to more distant clubs and hamfests if you can get me to your meeting and put me up overnight.
Ham Radio Publications
A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing NEW! This tutorial is directed primarily to RFI in ham radio applications. It includes an extended discussion of the use of common mode chokes as transmitting baluns, a section on audio and computer interconnections in ham stations, and extensive measured data on ferrite chokes. This document was recently revised to include measured data on chokes wound with transmitting coax, and an updated version of my Choke Cookbook. If you're building transmitting chokes (current baluns), you NEED this update! There's also a section on how to prevent hum, buzz, and RFI in your station without spending money on transformers or fancy interfaces.
Understanding and Eliminating RF Interference This is an updated version of the handout for a presentation to our local ham club on RFI and ferrites.
Measured Data For HF Ferrite Chokes This data was measured by a ham colleague using well calibrated HP instrumentation, and was published both in my AES Paper (see below) and in various tutorials. Here, all the plots are re-scaled to 1-100 MHz on the frequency axis and 10-1,000 ohms on the reistance/impedance axis to make it easier to compare one material to another and decide how to use these parts on the HF ham bands.
Ferrite Data for NCCC Group Purchase This is the same data as presented above, but with the addition of manufacturer's data for four other parts that will be part of the group purchase. All of these parts may be used for more than one purpose. For example, all may used to suppress RFI, and all may be used to build transmitting "choke" baluns for coax. To the extent that wire will fit through them, they may be used for single or multi-turn chokes. These parts are not generally suitable for winding HF or VHF transformers because they are too "lossy."
Power and Grounding For Audio and Audio/Video Systems -- A White Paper for the Real World This White Paper was commissioned by New Frontier Electronics (the SurgeX people) so they would have something to pass out to contractors and other users of their excellent power products. While it is written specifically for sound contractors and consultants, most of it is directly applicable to ham radio.
RFI and EMC Publications Written for Audio Professionals
New Understandings of the Use of Ferrites in the Prevention and Suppression of RF Interference to Audio Systems Building on the work of Muncy, the author has shown that radio-frequency current on cable shields is often cou-pled to audio systems by two mechanisms - "the pin 1 problem" and shield-current-induced noise (SCIN). An improved equivalent circuit for a ferrite choke is developed that addresses both dimensional resonance within ferrites and the self resonance of inductors formed using those materials, then compared with measured data. Field tests show that chokes formed by passing signal cables through ferrite cores can significantly reduce current-coupled interference over the range of 500 kHz to 1,000 MHz. Guidelines are presented for diagnosing the causes of EMI from sources as diverse as AM broadcast transmitters and cell phones. Solutions are presented for use in new prod-ucts and for RFI suppression in field installations. Preprint Number: 6564 Convention: 119 (October 2005) Author: Jim Brown
A Better Approach to Passive Microphone Splitting While there are clear technical advantages to active microphone splitting, operational considerations dictate the use of passive splitting of microphones in most sound reinforcement applications. Modern microphones generally require a load impedance greater than 1,000 ohms, and performance often degrades significantly with heavier loading. Since mix desk input impedances rarely exceed 1,500 ohms, passive splitting utilizing 1:1 turns ratio transformers can seriously degrade microphone performance when driving two or more mix desks. Transformers designed to operate in stepdown mode solve this problem and offer other benefits. This paper reviews current practice, studies stepdown-mode splitting, and reommends that mix desks be designed with higher input impedances and that microphones be designed to work with lower impedance loads. Preprint Number: 6338 Convention: 118 (May 2005) Authors: Jim Brown, Bill Whitlock
Testing for Radio-Frequency Common Impedance Coupling (the "Pin 1 Problem") in Microphones and Other Audio Equipment The author has shown that a primary cause of VHF and UHF interference to professional condenser microphones is inadequate termination within the microphone of the shield of the microphone's output wiring, a fault commonly known as the pin 1 problem. Tests using only audio frequency test signals generally fail to expose susceptibility to radio frequency (RF) interference. Simple RF tests for pin 1 problems in microphones and other audio equipment are described that correlate well with EMI observed in the field. Preprint Number: 5897 Convention: 115 (September 2003) Author: Jim Brown
A Novel Method of Testing for Susceptibility of Audio Equipment to Interference from Medium and High Frequency Radio Transmitters The author has shown that radio frequency (RF) current flowing on the shield of balanced audio wiring will be converted to a differential signal on the balanced pair by a cable-related mechanism commonly known as Shield-Current-Induced Noise. This paper investigates the susceptibility of audio input and output circuits to differential signals in the 200 kHz - 2 MHz range, with some work extending to 300 MHz. Simple laboratory test methods are described, equipment is tested, and results are presented. Laboratory data are correlated with EMI observed in the field. Preprint Number: 5898 Convention: 115 (September 2003) Author: Jim Brown
Pin 1 Revisited Neil Muncy called our attention to the Pin 1 problem (the improper termination of the shield of audio wiring to the circuit board rather than to the shielding enclosure) in his classic 1994 paper, reprinted in the June 1995 Journal of the AES. When he wrote his paper, most commercially available audio gear had pin 1 problems. It was, indeed, difficult to find equipment without it -- even the most prestigeous consoles had serious pin 1 problems! Over the next decade, the better manufacturers redesigned their products to correct their mistake, but sadly, many have not done so. This is the first installment of a two-part article published in the SynAudCon Newsletter.
Pin 1 Revisited -- Part 2 This is the second installment of a two-part article published in the SynAudCon Newsletter.
Understanding How Ferrites Can Prevent and Eliminate RF Interference to Audio Systems This applications note has been significantly revised and expanded since its first posting earlier this year. Even if you've read the earlier version, you should get this one. It has also been turned into an AES Paper for the New York convention in October 2005.
RF Susceptibility of Condenser Microphones Many modern condenser microphones have problems in the presence of strong VHF and UHF transmitters, like FM and TV broadcast stations, 2-way radios, and cell phones. This is an article published in the SynAudCon Newsletter. You can download a much longer and more detailed AES paper that David Josephson and I wrote in 2003 from the AES website.
Shield-Current-Induced Noise - Part 1 Current flowing on the shield of balanced audio cables will be converted to differential mode voltage on the signal pair by imperfections in cable construction. This is Part One of a series about this matter that I wrote for the SynAudCon Newsletter.
Shield-Current-Induced Noise - Part 2 This is Part Two of a two-part article published in the SynAudCon Newsletter. It also includes recommendations for the termination of audio cables.
Radio Frequency Susceptibility of Capacitor Microphones Neil Muncy has shown that improper termination of shield wiring, commonly called the pin 1 problem, couples noise currents flowing on a cable shield into audio circuitry through common impedance coupling. This paper examines the susceptibility of modern microphones, describes a simple test to find problems, and offers simple solutions. Preprint Number: 5720 Convention: 114 (February 2003) Authors: Jim Brown, David Josephson
Common-Mode to Differential-Mode Conversion in Shielded Twisted-pair Cables (Shield-Current-Induced Noise) Neil Muncy has shown that audio frequency current flowing on the shield of balanced audio wiring will be converted to differential mode voltage by any imbalance in the transfer impedance of cables, and hypothesized that the effect increases linearly with frequency. Whitlock has shown that conversion also occurs with capacitive imbalance. This paper confirms Muncy's hypothesis, and shows that shield current induced noise can be significant in the MHz range. Preprint Number: 5747 Convention: 114 (February 2003) Authors: Jim Brown,; Bill Whitlock
Publications on Sound Systems and Acoustics
Over the years, we've authored a number of articles and application notes to explain design concepts, help our clients understand complex issues, and help users get the most out of their sound systems. Here are some of them.
Giving Back This is a column I wrote for a newsletter for sound contractors and consultants.
Why Churches Buy Three Sound Systems, and How You Can Buy Only One Most churches are so afraid of buying sound systems that they do it three or four times before they finally end up with one that works well enough to meet their needs! Here's how you can do it right the first time.
Acoustics and Sound Systems in the Contemporary Church The contemporary church is built around communication - verbal, musical, and emotional - as well as worship. The minister communicates with the congregation by preaching, leading prayers, and announcing church activities. Music attempts to communicate ideas and concepts while it simultaneously enhances the worship experience through emotional involvement. The acoustics of the worship space have a profound effect on all of these functions. This article explains these complex issues in plain English for the non-technically inclined.
Wireless Mics and the Audio Professional This document was first prepared in 1986 for a seminar for the engineering staff at WGN Television. It has since been revised to make it more readable to the less technically inclined, and updated to keep up with new developments both in frequency allocation and technology.
Wireless Mics and Digital Television Our second applications note on wireless microphone technology addresses the impact of Digital Television on the wireless microphone landscape. If you use wireless mics you need to study both of these applications notes.
Which Coax for Wireless Microphone Antennas? This applications note, written for the SynAudCon Newsletter, shows that 75 ohm cable is much less expensive than 50 ohm cable, and works a lot better too!
Spreadsheet for Intermod Prediction This simple Excel spreadsheet illustrates the principles of intermod prediction. It can be used to predict intermod between up to five wireless frequencys and two broadcast carriers. It is also unprotected with all the formulas visible, so you can see how to expand it to consider more channels, or write a far more elegant one. I did this in an hour or so. See "Wireless Mics and the Audio Professional" (above) for a discussion of intermod and how to use the spreadsheet. Click here for the Quattro Pro version.
The Revitalization of a Community Landmark - The Greensburg Palace Theater The 1200-seat Palace Theater is an anchor of this small town on the western slopes of the Alleghenies just off the Pennsylvania Turnpike east of Pittsburgh. This blow-by-blow description of an historic renovation is a textbook example of how to do it right. We're very proud of everyone involved in this project!
Mixing for Three Channel Sound Reinforcement Two and three channel sound reinforcement is a concept whose time has finally arrived. Two and three channel systems are being successfully used in performance and worship spaces, on Broadway. and in theme parks. A well designed two or three channel system can blow the pants off of a monophonic system which uses significantly more powerful equipment. While this article (published in the March 1998 issue of Sound and Communications) was specifically commissioned to address mixing for these systems, it addresses our design philosophy for these systems as well.
The Acoustics of Sound Systems for Baseball was an invited paper presented to the annual meeting of the Acoustical Society of America in Chicago in June 2001. There is a lot of good information here about how sound behaves outdoors and when traveling long distances. Much of it also applies to sound indoors, especially in larger spaces. And here is a Power Point (97) presentation with a lot more graphs and graphics to go with it.