Troubleshooting Common RFI Problems

What is RFI?

RFI (Radio Frequency Interference) happens when RF energy gets where it shouldn't. This can go two ways:

• Your transmitter interferes with other devices
• Other devices interfere with your receiver

Common RFI Symptoms

Transmit RFI (Your Station Causing Problems)

• Computer resets when you transmit
• LED lights flicker
• TV or stereo makes noise during transmit
• Hot microphone or RF burns
• SWR changes when you touch things

Receive RFI (Other Things Causing Problems)

• Buzzing or humming on received signals
• Hash across the band
• Noise that goes away when you unplug something
• S-meter readings with no signals

Finding the Source

For Transmit RFI

Reduce power and see if the problem decreases

Check all bands - problem may be worse on some

Walk around the house while transmitting (carefully) to locate affected devices

For Receive RFI

Turn off circuits at the breaker panel one by one

Use a portable receiver to hunt the noise

Check if noise is present on all bands or just some

Note if the noise has a pattern (on/off, cycling)

Common RFI Sources

Your Station

• Common mode currents on feedline
• Poor station grounding
• Antenna too close to the house
• RF getting into microphone cable

In Your Home

• LED light bulbs (especially cheap ones)
• Switching power supplies
• Computer equipment
• Solar panel inverters
• Battery chargers
• Touch lamps
• Dimmer switches
• Plasma TVs

Outside Your Home

• Power line noise (arcing insulators)
• Grow lights
• Electric fences
• Neighbor's devices

Solutions for Transmit RFI

Choke Common Mode Current

The #1 solution. Add ferrite chokes to:

• Feedline at antenna
• Feedline at shack entry
• Power cables
• Computer cables
• Microphone cable

Improve Station Grounding

• Single point ground for all equipment
• Short, heavy ground straps
• Good earth ground connection

Increase Antenna Distance

Get the antenna further from the house if possible.

Use a Tuner Wisely

A tuner helps your radio, not your feedline. If your feedline has high SWR, you may have more RFI.

Filter the Affected Device

Add ferrite chokes to the cables of devices that are affected. Clip-on ferrites work well.

Solutions for Receive RFI

Find and Eliminate

If you can identify the source, fix it at the source. Replace noisy LED bulbs, move chargers, etc.

Filter AC Power

• Use AC line filters
• Isolate your station on its own circuit

Common Mode Chokes

Chokes on your feedline help receive noise too.

Noise Cancellers

MFJ and others make noise cancelling units that can null out specific noise sources.

Directional Antennas

Some antennas can be aimed to null out the noise direction.

Specific Solutions

LED Light Bulb Noise

Replace cheap LEDs with quality brands (Philips, GE). Some hams have success with incandescent bulbs in problem areas.

Computer Noise

• Ferrites on all cables
• USB cables are often culprits
• Ethernet cables can radiate
• Consider powerline ethernet adapters (they're terrible for RFI)

Solar Panel Inverter

Contact the inverter manufacturer. Many will provide filters. FCC regulations require them to fix interference.

Power Line Noise

Report to your utility company. They're required to fix it. Document with recordings and time stamps.

Prevention

When building your station:

Plan for single-point grounding

Include chokes from the start

Run feedlines away from power wires

Use quality feedline and connectors

Choose quality power supplies

Resources

• ARRL RFI page: arrl.org/radio-frequency-interference-rfi
• ARRL Technical Information Service can help with RFI
• K9YC's RFI tutorials are excellent technical references