Week #10: (3/25-29) EMI

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rjagodowski
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Joined: Fri Sep 04, 2015 6:59 pm

Week #10: (3/25-29) EMI

Post by rjagodowski » Thu Mar 28, 2019 7:35 am

This week we will pick up the discussion of Electro-Magnetic Interference beginning with the content posted at the end of Week 9.

Then we will discuss the highlights of the pdf attached below on Electromagnetic Compatibility.
ElectroMagnetic Compatibility.pdf
(5.44 MiB) Downloaded 24 times
This is a fairly lengthy (200+ pages) document which addresses the concept of dealing with EMI & RFI with a focus on maintaining compatibility among systems which occupy the same spectrum space. It is written at a "technician's level" with minimal emphasis on mathematical equations, numerous diagrams and clear and concise descriptions of problems and their solutions.
While we don't have time to cover the entire document in class (it could be a course all by itself), I encourage you to put this on your "reading list" to read in its entirety.

One of the key concepts you should grasp from this reading is that wire which appears to be just a resistive element at low frequencies behaves like a complex impedance at higher frequencies (typically 5-10 MHz & above). This understanding is critical when dealing with cabling used for high frequency analog and digital signals such as cable TV and computer networks. The cable that is used for each application must meet specific requirements. In the case of video circuits, 75 ohm impedance cable and circuits are used and in ethernet applications the cables and circuits are 100 ohm impedance.

One of the concepts presented early on in this document is the concept of harmonics. Here is a simulator that we'll discuss in class which shows the relationship between waveform shape and harmonic content. www.Falstad.com/fourier.

In order to better understand some of the concepts presented, it is helpful if you have a fundamental knowledge of how waves travel.

Here is an animated presentation of an electrical signal travelling down a transmission line model (4:58) complete with inductance and capacitance.

This YouTube Video from Bell Labs in 1959 (28:02) very nicely demonstrates various aspects of wave motion and impedance using mechanical waves. Watch this video.

An instructional video which deals strictly with Electromagnetic Waves is presented here, taught by Sir Lawrence Bragg (20:22).

YouTube video of Standing Waves on a Transmission Line viewed with an Oscilloscope (10:50).

Here is a link showing the Characteristic Impedance of Free Space and this is another with a more mathematical presentation. Here is one on Antenna Impedance.

Antenna Basics and Antenna Patterns and their Meanings from Cisco systems. Much more detail than is expected to be presented at the level of this course, but I supplied these links as a general introduction to the complexity of antenna design. The Cisco link has some decent graphs showing antenna radiation/reception patterns, which could be useful when trying to understand how RF signals will propagate from an antenna, such as a cell phone or wifi router.

Presentations on Crosstalk from Wikipedia, Polar Instruments and ad-net.com.

Here is a link to the topic of Ground Loops from Wikipedia.

Drain Wire for grounding

Shielding and Grounding in Industrial Automation.

The 50 Ohm Question: Impedance Matching in RF Design.


Also a topic for discussion: Cabling Concerns - Check out the short video "Moving Violations" on Cable & Power Cables in Contact, violating code regulations in ECM CodeWatch from June 2, 2016.

This YouTube video shows how Ferrite Beads are used to suppress EMI.

Electrostatic Discharge - Causes, Effects & Solutions.

Here's a few observations about ESD (Electro-Static Discharge).

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