RFI – short for Radio Frequency Interference – is a constant battle for the modern ham radio operator. For every electrical device, there is a risk of interference somewhere in the radio spectrum.
For hams, there are 2 types of RFI, and this article will break them both down separately.
Transmitted by your station – your signal causes unwanted interference to an outside device
Received by your station – a spurious signal from a nearby device affects your radio receiver.
Transmitted RFI
What causes RFI?
When you look at any circuit, you will see individual traces on the circuit board or wires used with the device. These are all made of copper and conduct. Unfortunately, with any length of conductor, it may be a perfect length to behave like an antenna. When traces and wires behave like antennas, it may affect the circuit in unexpected ways.
How can I tell if it is RFI?
Simple – if you are transmitting and things suddenly behave strangely, you are causing interference to that device. If you use mroe power, you may notice more extreme behaviors. This may happen with some bands or all of them.
Some pretty common symptoms of RFI
Amplified speakers buzzing, humming, or hearing voices.
Touch sensors erratically being triggered
Network devices stop working, or the Wi-Fi signal is affected
Received RFI
This type of RFI is the bane of amateur radio operators everywhere. There is a chance that any device may emit unwanted noise on the amateur bands.
What does it sound like?
It depends on the source.
What common items cause RFI?
Electric fences
Power lines/power line transformers
Lightbulb dimmers
LED Lights
faulty switches
Arcing power sockets
Touch lamps/touch devices
Variable speed motors
Unshielded/poorly filtered AC to DC wall warts
Cable TV boxes
Solar panels/power inverters
Grow lights
Data over powerline
Engine ignition
Bug zappers
Neon signs
Battery chargers
What does RFI sound like?
It can sound like lots of things! It can sound like static, a constant carrier, uneven pulsing; there are so many possibilities. But all of them are unwanted noise that masks wanted signals.
How do I reduce RFI?
First: Identify the sources of RFI in your location. That is an entire topic by itself. You can read more about it here: DIRECTION FINDING. Suffice to say, a tuned receiver and directional antenna are needed for this step. Find the source of the noise. You can verify if this is the source by unpowering the offending device. If the noise stops, congrats, you found it!
Mitigate the noise
This step can be tricky, because there are multiple ways to do this. First, if this device does not need to be op while you are operating, it is very easy to unplug it
What if the source is in a neighbor’s home or yard?
This is very tricky! First, you should be a good neighbor. Being friendly with your neighbors may make this step possible. If you are a nasty neighbor, your RF requests may be ignored. Some neighbors may be nice and allow you to buy the offending devices or will accept a better version of an item.
Maybe they don’t want to sell the item or get rid of it. Now what? We now talk about the magic of ferrites. Try to add ferrites to the power cord or other wires.