[RFI] Wiring practices to minimize emissions

James Gordon Beattie, Jr. w2ttt at att.net
Tue Jul 12 14:00:57 EDT 2016


A couple of key points to consider for the benefit of both the public and the city:

1. Noise from large industrial or commercial equipment can be as tough to predict and mitigate as consumer devices. 

2. Noise from Part 15 anf 18 compliant devices can raise the overall noise floor and impact spectrum through 900 MHz and beyond.  

3. Public safety, cellular, landmobile radio and Amateur Radio can all have their effective coverage reduced, which endangers, or least inconveniences the public and officials while also driving up costs related to overcoming or mitigating the noise.

4. AM, FM and TV broadcast reception is also impacted, which is a further inconvenience and safety issue.

5.  All of these can be subtle, but it is when systems are challenged to perform at their limits, they don't need additional issues with noise.

Your point about integration testing should be in your acceptance plan.  Getting solid before and after data is going to be key.  The additional challenge is that there is so much in the way of noise sources in the existing RF ecosystem, that you may have trouble getting a solid, but relatively quiet baseline.

One idea is to measure similar sites when they are online and offline as the basis of comparison.  Getting to a station during an offline or maintenance period may be tough, but you may be able to measure the system as it cycles on and off under load as a baseline.

The use of an R&S PR-100 will reveal things not normally seen with standard spectrum analyzers.  For low frequency stuff, Radar Engineers has some interesting tools that you might want to investigate. 

Finally, the Part 15 and 18 regulations and standards are set up to eliminate the most egregious devices from going directly from the production line to the field and their standards are generally weak and device-oriented instead of being system-oriented.  Even with those standards, but even with them there are plenty of.non-compliant, or marginally compliant devices generating RF noisE and causing issues.  

There is nothing preventing you as the customer from specifying a higher performance objective than what is defined in the FCC regulations and the standards they reference.  Put the higher quality requirements in your RFP/RFQ.  I'm not sure where I would start, but perhaps somewhere in the 20-30 dB better than what the regulations and standards require would be a good starting point, as you want to protect the public from these aspects of RF emissions.

Systems need to be checked as a whole and re-checked as part of annual maintenance.  You might consider putting that in your RFP/RFQ as well.

Vy 73,

Gordon Beattie, W2TTT


Sent from AT&T Mail on Android

From:"nm8rmedic via RFI" <rfi at contesting.com>
Date:Tue, Jul 12, 2016 at 11:56
Subject:[RFI] Wiring practices to minimize emissions

There are a couple participants on this board who have direct experience with industrial wiring practices that minimize radiated EMI emissions. 

I am a city manager and have the opportunity to discuss with a major manufacturer the wiring design of a large sewage lift station they are building for us, to minimize EMI emissions.   

They tell me that while the individual components meet Part 15 and Part 18, they have never tested the package as a whole. 

I would appreciate some input from the group on talking points.  This could also be the chance to influence wiring design for many of this manufacturer's lift station packages.


and want to maximize the opportunity when I speak with the engineers.

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