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Author Topic: QRM from power grid.  (Read 633 times)

Posts: 5

« on: November 16, 2008, 03:09:23 AM »

Hi All,

About a month ago some mysterious pulsating QRM started showing, ranging from 400KHz to about 90MHz.

The QRM is a repeating click with a 250 milliseconds interval. The click is 40 DB over S9. Very loud.

I started my investigation but I cannot locate the source. It looks like the click is transported over the 230Volts power lines in my house and also in the houses of my neighbours. But it's the same strenght everywhere...

Does anyone have some tips how I can inverstigate further? Or does domeone have experience with this kind of QRM?


Posts: 6252

« Reply #1 on: November 16, 2008, 04:21:57 AM »

You need some specialized gear--an attenuator, for one thing.  You've got to cut down the 'overload' that keeps you from seeing the direction of the source.  Get in touch with your local club, and see if someone can point you to one of the memebrs who does direction finding or fox hunts. They may be able to help you out.

Posts: 0

« Reply #2 on: November 16, 2008, 05:43:50 AM »

What you might do is the following....

And for those who read this post the poster in in Euro Land and not subject to the FCC Rules so ya might want to keep that in mind in your reply.

First thing is to completely disconnect the antenna from the radio and listed to see if the noise goes away (or not).  IF the noise goes away then the interference is cimming thru your antenna.  If the noise does not go away the noise is comming thru your power line.

Now lets say the noise is comming thru the power line.  You can buy and or make a "Brute Force Line Filter".  This filter is installed directily on your power line into your radio.  Get an older version of the ARRL Handbook and look it up for a diagram of how to build one.

IF the noise is comming thru your antenna (the noise goes away when you disconnect the antenna from the radio) then the problem lies elsewhere--the power lines themselves or a neighbor.  Check with the Rules and Regulations governing Amateur Radio in your particular country.  Take whatever steps as are stated in the rules and regs of your country and HOPE that the Rules Enforcement Division of your country cares.


Posts: 1697

« Reply #3 on: November 16, 2008, 12:14:30 PM »

The techniques suited to identification and measurement of BPL (PLC) emissions may be relevant.

Here is the antenna I used for measurement: . It is highly directional, so it can be used to identify the emission source.

Here is the software I used for measurement of field strengths (in dBµV/m) using an ordinary SSB receiver and a known antenna (such as the loop above): . You will find lots of links to relevant reports etc that may give you some idea of how to report your findings to the relevant authority.


Posts: 625

« Reply #4 on: November 17, 2008, 07:43:07 AM »

Since you can hear it in the AM broadcast band, use a portable AM radio with a ferrite loop antenna.  You can rotate it for a null and tell what direction the source is.  Follow the power lines around and see if you can find a spot where it is really strong.  I found a neighbor who had a malfunctioning GFI in his bathroom by doing this.  It was possible to track the noise to his house by following the underground utility wires to his house.  I think it would work for overhead wires as well.  Once you locate the source generally, you turn off circuit breakers one at a time until you are able to shut off the source.  Then figure out everything plugged into that branch and investigate each one with the AM radio.  Unplug the culprit and your noise should go away.  Fixing the culprit is a whole nuther post.

Posts: 5

« Reply #5 on: January 25, 2009, 02:34:55 PM »

Hi Guys,

Thanks for all the tips and tricks you provided me. The QRM is gone, but let me tell you my story:

The strangest thing happened. I built a directional antenna to connect to my TH-F7 portable trx. I started to track down where the QRM was coming from and I ended up at my neighbors house. I kindly asked if I could measure inside the house, and this was no problem. I could not find the source, but one thing was for sure. I was very close.

But as unexpected as it appeared, it disappeared the same weekend! I asked my neighbors if they had changed anything that weekend. They said they did not change anything in their house or garden. I believe and trust them completely, so I am sure they did not have anything to do with it. But it left me in the dark. I could not identify the source.

I am very, very glad the QRM has gone, but it leaves me unsatisfied that I could not find the source!

Twan the PA8TWN
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