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I have RFI, now what– Quantification

Posted by on June 23, 2014
Example of RFI

Example of RFI

So I have RFI, now what– 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.  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, see the movie above.  In this set of articles, I will describe the process I used to locate and mitigate RFI 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.  See the movie above for the RFI as it looks from my QTH.  Hit play, and all looks well until about 22:30 GMT, which is about 3:30 PM in my local time zone.  As you can see, the RFI goes off scale at that time.  The S Meter reading for that signal is around 10 db over S9.  It is also affecting three other hams in the area.  One poor fellow is so close to it that all ham bands are wiped out,  160 Meters through 10 meters are unusable during this time frame.  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.  So there are folks who have it worse than me in this!  Note this is an older recording, currently the start time for the RFI has changed to 01:36, or 7:36 PM local time, running all night, then ending aroind 7:30 AM PLT.

All in all there are 4 and possible 5 hams affected by what is a single source, over one or 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.

The first step in quantification was to verify we were all being affected by the same source…  That was pretty easy, we all started listening at 7:30 PM, and waited until 7:36.  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.

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 will be what I did to monitor, and characterize the RFI.  The next article will cover how I will be using 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 for 10/14/12

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.

S-Meter Lite:

S Meter Values for RFI 10/14/12

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.  That helps in scheduling your hunt times.  See the graph below for an example.

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 teh results in a form which Libre Office, or Microsoft Office can can use, this software is for you.  Best of all, it like Spectran 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.

Soundcard Scope:

Soundcard Scope

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.

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…


One last tool…  Your RFI logbook.  You need to be sure to keep one.  It should contain every conversation you have with the Power Company, your neighbors, and/or any people you talk to about the RFI they are generating.  It should contain , anything you learn about the RFI, for instance, start times, stop times, who heard it, signal strengths, weather conditions, etc.  All if this may come habdy if you talk to someone again, or if you file an FCC report.  If you don’t have a log, go home, and stop trying to locate your RFI…  You are wasting your time doing this if you are not keeping a log.


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.  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.  The next step was to build and use a loop to help locate the source.  All of this data was noted in teh logs, for a later report to the FCC if needed.


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 5 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 Service operators, this makes it easy to locate.

6.  The RFI is more than likely a grow operation.

The start times, and end times are very helpful…  If for instance, the start time is changing with the sunrise time, then I probably have something like a street lamp, as opposed to a timer.  This lets out the street lamps because the time is rock solid, for both start and end times.  Having five 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 once the loop antennas are finished.  Given one of the five hams is loosing all HF 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 suspect it is a grow operation because of the light timings…  About every six weeks things change during I presume harvest time.  So I have learned a lot from just a few tools, and never had to leave the shack…  I will be putting up a Google map of the RFI in the area soon, as I have a project almost finished to map the RFI using GPS and a computer, coupled with Google maps.

I also build a good base for a report to the FCC, if needed.  In a previous hunt, I located the source, and used the log as evidence for the FCC report.  The FCC sent a letter, and the problem went away.  My goal now is to not waste the FCC’s time, but to be able to hand them something they can work with, and that they trust as accurate.  To me, that is of paramount importance.  I want the FCC when they see something from me, to realize that a lot of checks went into it, and to believe I am not shooting from the hip so to speak.  The last thing I want is for the FCC to ignore something I submit to them.  That means playing by their rules, and providing good data to them 100% of the time.  Not 90%, but 100% of the time.  Everyone involved is strapped for money, anything you can do to help will make the agency you are dealing with trust you more, makes it simpler for them to solve your problem.

Part II:

Part two will focus on how to make sure your own house is clean, it can be found here.

Part III:

Part two if this will focus on the methods for triangulation on 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.    In any case, Part II will provide actual examples of how I triangulated on a RFI source, while Part III will provide what I did once I located the source.  Part II will be up in about a month…

4 Responses to I have RFI, now what– Quantification

  1. Dave

    Next part should come out today or tomorrow Alex.

  2. Alex

    Very interesting. I need make search of RFI here. I`ll be wait next parts

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