LOCATING INTERFERING NOISE
Unwanted noise is a big problem. With so many devices that make noise, it is a challenge to keep your receiver reception clean.
There are power line noises. When a power line or transformer arcs to ground, it can generate noise for several miles. The arcing can
go on for years without burning anything out on the electrical grid.
There are noises generated by other electronic devices. Wall warts are notorious noise makers. It can wipe out the reception for HF.
Computers and tablets can generate noise, however if the power source is clean they are not as much of a problem.
Finding the source of man made noise can be a challenge. Noise will most likely appear around 7 Mhz the strongest. 3 - 4 Mhz can be
almost as strong. Going lower to the 160 meter band may be quieter. At 10 MHz and higher the noise can be quite low.
The first place you want to look for noise is in your own home. Power up your receiver with a battery. Make sure you are hearing
the interference well. Then go to your electrical panel. Turn off one breaker at a time. If one of the circuits drops the noise out,
you got off easy. Now you can look for the offending device.
If it is a power line, it will be a bit more challenging. You can use an AM broadcast radio with a built in ferrite antenna. This
will give you two directions that the noise may be in. However, sometimes the interference is not affecting the AM band much. That
will require listening on the Amateur bands that are most affected.
Being able to receive in a vehicle may get you close by watching carefully the signal strength of the noise. Most power lines are
delivered to a community by a three phase line. You will see three hot lines, normally in the same plan and a fourth line underneath.
From the three phase it can branch off to a single phase having only two wires on the pole. This line will feed the transformers
that supply the homes.
Turning down the attenuator on your HF radio, you can locate the most intense spot the noise is being produce.
If you are able you can switch antennas on your vehicle to the ferrite antenna for the HF band you are listening to. This can be
made from a ferrite rod. Wrapping a few windings of thin magnet wire on the rod and connecting it in parallel with a variable
capacitor. A lesser number of winding can be added to the rod in the center of the rod and attached to a connector. With a little
experimenting you can get the ferrite to resonate on the frequency you are listening to.
This will give a bi-directional antenna. Normally it will point to the pole, measuring signal strength. The strongest signal will put
you close. Even with this arcing, you may not hear it.
Now what do you? Chain saw?, Shot gun?
Most power companies have sophisticated equipment for noise detection. This equipment may be unknown to much of the power
companies staff. It would be best to contact an engineering or technical department to request help in finding the offending
device. If you get the right person, the noise can normally be located quickly.
73,
Ralph WD0EJA
02-2019