browser icon
You are using an insecure version of your web browser. Please update your browser!
Using an outdated browser makes your computer unsafe. For a safer, faster, more enjoyable user experience, please update your browser today or try a newer browser.

I have RFI, now what– Part III, Quantification

Posted by on June 23, 2014


Example of RFI as displayed by both Spectrum Lab, and S-Meter Lite.

Example of RFI

So I have RFI, now what– Part III, Quantification, gathering the tools:

This first part will cover gathering the software tools I used for RFI location and removal, while part II covers cleaning your own RFI up.  Or look here for the entire series.  Quantification, followed by location of the source, that is the first thought that came to my head when I discovered the RFI being sprayed all over the area I live in.  In this set of articles, I will describe the process I used to locate and mitigate a few RFI sources around my area.  Your mileage may vary, and you will need to remember, this is what I did, and not a guide for you, but more of a chronicle of events and actions I took to solve my RFI problem.  Here is the legal disclaimer: None of this should be construed to be a suggestion as to what you should do, that is something you need to decide on, this is what I did, and am doing.

The Problem:

Over the past few years my RFI problem has been getting worse and worse.  40 Meters was unusable due to QRM last year, I am only now beginning to be able to use 40 meters again, after shutting down three RFI sources in the local area.  Other hams in the area, (1/2 mile away), closer to the source of the RFI have lost the entire HF spectrum.  this poor fellow had all ham bands wiped out, 160 Meters through 10 meters, 7X24X365, for two years.  There is another ham located about 1/4 mile from the source, he has just moved in, and was unaware why his use of 40 meters use was precluded due to RFI.  Yet a third fellow up the road was getting wiped out.  So there are folks who have it worse than me!

All in all there are 6 and possible 9 hams affected by what was a single source, over several square miles, all from a single source.  We have the general area pinned down, and this summer, (2014), we are going to locate the house, and either contact the owner, or request FCC assistance.  A report has already been filed with the FCC regarding the RFI levels in this area.  That was done a few weeks ago.

In order to file these reports with the FCC you need to first quantify the problems with real numbers, not just my radio is unusable but real numbers, signal levels, field strength readings around a suspect location etc.   You need to tie the RFI source to each station being affected in order to be able to prove it is the same source.  In this case it was pretty easy, we all started listening at RFI start time,  and waited until 10 minutes.  We all heard the RFI start at the same moment.  That pretty well indicates that the RFI we are all hearing is the same.  It also has the same start-up sound associated.  Each person took recordings, and each person time stamped them for later use with the FCC.

In order to be as efficient as possible in this, the first thing was gather as much information about the signal as possible.  For that we needed some tools… They are both free, and they are very high quality.  Once the tools were in place, all I needed to do was to define the hours of operation for the RFI.  That way I could efficiently schedule my RFI hunting, and use the start times to verify that the same source was in fact covering several square miles of area.  This first article show what I did to monitor, and characterize the RFI.  The next article will cover how I used triangulation to locate the individual houses involved.  Here are the tools I used to quantify the RFI, and get set to locate it.

Spectrum Lab:

FFT of 24 hours of RFI as shown by Spectrum Lab.

FFT for 10/14/12

Here is what the Spectrum Lab web site says about Spectrum Lab:

This program started as a simple FFT program running under DOS a long time ago, but it is now a specialized audio analyzer, filter, frequency converter, hum filter, data logger etc (see history). You can download it from this site. Or look into the manual (in HTML format), even though the manual included in the archive will be more up-to-date. Furthermore, the same manual has occasionally been converted into a single PDF (SpecLab_Manual.pdf), but any attempt to create a common index and table of contents for this PDF, using OpenOffice (with proper page numbers instead of the hyperlinks) has failed miserably – see note in the preface of the PDF document.

For the most part I agree, but here is a simpler explanation of what SpetrumLabs does:

SpectrumLabs will graph your audio passband, vs. time, and show amplitude as well…  Further it will save an image at a regular interval of that graph.  It will do a LOT more, but for my use I decided on SpectrumLabs because of the ability to graph the audio bandpass of my rig vs time.  Some folks don’t think it is useful to do this, but I am one of those people that likes to collect data, so this seemed to me a good tool for data collection.  Here is where to download SpectrumLabs. Here is a move of the latest source in South Eugene.

RFI Fingerprint

This fingerprint makes it pretty simple to tell what the cause is if you have seen enough of them.  It also can be used when opening an RFI case with the Federal Communications Commission.

S-Meter Lite:

RFI graph, generated by Libra Office, and S-Meter Lite.

S Meter Values for RFI 10/14/12

S-Meter lite is so useful in RFI hunting.  Again, it lets you quantify the start and stop times for your RFI, as well as the signal levels.  For instance here we see a level of 10 db over S9, which corresponds to a direct power level of 150 micro-volts into your 50 ohm antenna, in my case at about a half mile from my site.  This is clearly above the legal Part 15/18 limits at 1/2 mile away.  In fact, if it were 30 feet from your antenna, and reduced enough to generate the same signal level it would still be above FCC limits.  As can be seen, and more importantly measure here, this source is in clear violation of the law.  Again, keep these data files for use later with the FCC.  The FCC will perform enforcement actions based on this type of data.

Here is what the S-Meter Lite web site has to say about itself:

S Meter Lite is a no-cost program that displays your receiver’s S Meter signal strength in a window. The next picture is an S Meter Lite screen capture.


Here is what I have to say about it:

S-Meter lite is written by W8WWV, (Cool call sign BTW), and can be found here.  S-Meter lite can serve to perform a couple of duties here.  It can assist you in deciding when to hunt, and it can help in IDing the source…  S-Meter Lite has a mode for constructing beam patterns as well, all in all, this is a very handy piece of software, and it is stable as a rock.  I have let it run for days… Never a problem of any kind.  If you need to graph S-Meter values, and get the results in a form which Libre Office, or Microsoft Office can can use to generate graphs as you see above, this software is for you.  Best of all, it like SpectumLabs, it is free!  Be sure to write the authors and thank them if you use the software.  If you are interested in this software, I have a review of it here.  I run this whenever there is an active RFI source running.  I keep every graph, and comple them into a packet for the ARRL/Federal Communications Commission in the event a case needs to be opened up with the Federal Communications Commission.  Add a laptop, and a car to this software, and SpectrumLabs above, and you have a portable monitoring point you can park near the RFI source and take readings for later use with the FCC.

Soundcard Scope:

Single freeze frame of RFI pulse as shown by Soundcard Oscilloscope software.

Soundcard Scope

Next you will need an Oscilloscope program so you can make sure the RFI you are seeing at one location, is the same as the RFI at a different location.  I tested several, and this program seems well written, stable, and never crashes.

Here is what the Soundcard Scope site says for itself:

The PC based Soundcard Oscilloscope receives its data from the Soundcard with 44.1kHz and 16 Bit resolution. The data source can be selected in the Windows mixer (Microphone, Line-In or Wave). The frequency range depends on the sound card, but 20-20000Hz should be possible with all modern cards. The low frequency end is limited by the AC coupling of the line-in signal. Be aware, that most microphone inputs are only mono.

The oscilloscope contains in addition a signal generator for 2 channels for Sine, Square, Triangular and Sawtooth wave forms in the frequency range from 0 to 20kHz. These signals are available at the speaker output of the sound card. These can be fed back to the oscilloscope in order to generate Lissajous figures in the x-y mode.

Here is what I say about it:

This is a sound card oscilloscope program that will allow saves of the image generated.  It is a full featured O-Scope, and it is also free, however the author asks for a donation for non commercial use.  You should consider this, the program is really well written, has a lot of features, and works like a dream, you can obtain it here.  It allows you to save your scoped RFI patterns, and it allows for triggering on amplitude, so you can guarantee a good trace.  All in all this program is wonderful, and works well.  Again, save this output as well.

Portable Short Wave Radio:

I have a Yaesu FT-817 portable battery powered SW radio I use during locates.  I have several different antenna I use, consisting of a yagi, and several small handheld loops.  With these, I can usually pin a source down to a single house, and tell you which side of the house it is on all from public street access, and in less than 15 minutes, just from the RFI leakage alone.  It is surprisingly easy to locate a source.  For power poles I have a three element yagi for VHF, and a ultrasonic pin-pointer for sparks on poles.

Google Maps:

Get a map of your area from Google, use it for getting the feel of where your RFI source is.  I keep track of the sources on a non-published map.  One tends to spot trends in an area that way.  Also, you can use the air photo, to triangulate on the source later…  Google maps are invaluable tools…  I use them to locate the RFI source.  It takes pretty much about 10 minutes to locate a source now, it is surprisingly easy once you have done it a few times.  I plot the sources on a map, (there is an app for that), and keep it for use later with the FCC.  With just a few very simple tools I can draw direction bearings on the map, and this makes it simple to locate a distant source.  Once I am in the area, I use a hand held loops to locate the RFI source, again drawing triangulation bearing lines on a map, and again keeping this for later use by the FCC if need be.


One last tool, and my most important one!  The RFI logbook.  I insure my log contains every conversation I have had with the Power Company, my neighbors, and/or any people I have spoken with about the RFI they may be generating.  The log contains anything I learn about the RFI– start times, stop times, who heard it, signal strengths, weather conditions, location methods, equipment used etc.  All of this may come handy the next time I speak to someone, or next time I need to document a signal strength level.  More importantly it is most important, if I decide to open a case with the FCC.  The log ties all of my other tools together for the Federal Communications Commission when they review the process I used to locate the RFI source.

I never forget I am compiling something which will become a legal document if I decide to open a case with the FCC, so I keep it objective at all times.  I also remember my goal, I am trying to stop the RFI, not get the FCC involved needlessly.    I try and get my neighbor to become part of the solution, not the problem…  But I also remember, if I decide to open a case with the FCC, my log will be looked at be many federal officials, FCC and otherwise, so I keep it objective at all the times.  The last report I compiled for the FCC was about 15 pages long, and the FCC send an enforcement letter directly off that data.  The problem ended when the person involve received a registered letter, return receipt requested, from the FCC telling him he had 30 days to comply, and 30 days to write the commission back with exactly what steps he had taken to comply with Part 15/18.  This did not have to go this far, and it really is too bad that things had to go that far, but the person involved refused to deal with the issue, so opening a case with the FCC was the only course of action available to solve the RFI issue.

I never want to take it this far unless it is really necessary, it complicates the life of the person generating the RFI, and is not a friendly thing to do, so I try to make my thoughts understood, please fix this, else I will file a case with the FCC.  Our club, has a handout we give to people for this sort of thing.  It is friendly, and in general tries to solve the problem at the local level first, it has also been reviewed by a lawyer as well, to insure it is correct and useful to the FCC.  I make a single attempt to solve the issue by contacting the person I believe is causing the RFI, and I leave a copy of the handout.  If the RFI continues more than 30 days beyond that time, I contact the FCC and turn it over to them.  I would like to avoid Federal Communications Commission involvement, but I will not have my hobby of 50 years destroyed so someone else can enjoy their hobby, when they are breaking the law.  I have spent considerable money and countless number of hours insuring I am not interfering with others, and I expect the same treatment for them.


Now that I could visualize my RFI problems in several different ways, instead of just sitting in front of the radio, I began to inspect the graphs and images to see what I could learn prior to starting the hunt.  The first thing I could learn was that there is a start and stop time.  In one case, that enabled all of us involved to make sure we were being hammered by the same RFI source.  We were…  We all got on the phone at the same time, and started listening.  At the EXACT same moment for all of is, the RFI would begin.  We were all also running S-Meter Lite, and we had our clocks synchronized as well, this helps in removing any human bias, and we all had records of the exact start time, this ties the same source to the RFI being heard by all of us.  The next step was a drive around, or two, to get a rough area, and then to use a handheld loop to locate the source.  All of this data was noted in the RFI log, for a later report to the FCC.  To see what various sources of RFI look like as visualized by SDR, visit the RFI Signature portion of this web site.


With just these tools I was able to decide, when to look, where to look, what tools to take with me to look, and how to proceed, once I started DFing the source.  For instance, by using these tools, I have been able to learn the following:

1.  The RFI has a well defined start time.

2.  The RFI has a well defined end time.

3.  The RFI is being heard by at least 7 other hams.

4.  The RFI is covering a very large area, several square miles.

5.  Based on signal strength reports, the RFI source is within 1000 feet of one of the affected Amateur Radio operators, this makes it easy to locate.

6.  The RFI is more than likely a grow operation of some sort.

The start times, and end times are helpful, but not necessary…  If for instance, the start time is changing with the sunrise time, then I probably have something like a street lamp causing the RFI, as opposed to a timer.  Having seven other hams hear the RFI lets me know that it is very strong, and gives a rough location to start with, making it a simple matter to locate.  Given one of the seven hams is loosing all HF, (80 through 10), at the time it starts, and that the signal is something like 30 to 40 over S9, he lives very close, probably less than 500 feet.  This further helps to limit the area to search in.  I have learned a lot from just a few tools, and never had to leave the shack…  I have a project almost finished to map the RFI using GPS, a car, and a computer, coupled with Google maps, it will give a complete overview of every RFI source in area.

In a previous hunt, I located the source, and used my RFI log, along with many other documents as evidence for the FCC case filing.  The FCC sent a registered letter, return receipt requested, and the problem went away, and the person involved had to outline in detail to teh FCC exactly what they did to correct the RFI issue.  Most of the time this does not need to happen, the people involved, be it the Power Company, the telco/cable, or a private individual all seem reasonable, and seem to get it– generating copious amounts of RFI, and interfering with a licensed station is not legal, and it needs to be solved.  If it continues beyond the point where that person has been notified of the issue, it can then constitute intentional interference, which has even higher fines than generating RFI.   I only bring in the FCC when the entity I am dealing with refuses to work on solving the issue, which is sad, but every so often I run into one.  Our club is now working directly with the local power company, the cable company, and the local telcos to locate RFI issues.  They all understand that if they are causing RFI, they must correct it in a timely manner, and they have all done a really fine job in this…  I have nothing but good to say about utilities at this time.  So all in all this process is working, and it minimizes the need for opening a case with the Federal Communications Commission.

Part II:

Part two will focus on cleanup of my own shack, it can be found here.

Part III:

Part three focuses on the methods for location of RFI signals.  There are many sites for loop construction, one I used for construction of my loops being that of W0IVJ.  His site covers how to build a loop and receiver.  If you have a portable receiver, just build the loop.  If you have a mobile setup like I do, you don’t need the RX, use your car.    Part III will provide what I did once I located the source.

0 0 votes
Article Rating

Please feel free to leave a comment.

Oldest Most Voted
Inline Feedbacks
View all comments
Mark L. Wuori
2 years ago

I’d like to know what the RFI came from. If it was a device, a utility or what.
Other than that, I think you did a terrific job on documenting all of the problem. The information you have given is invaluable.
Thanks for writing it up.

Sincerely Mark L. Wuori

4 years ago

Excellent site and info. Thank you.
Wendell, K8OO