AmateurRadio.com

Without any RFI issue.

In my last post, I was on the receiving end of RFI—you can read about that HERE. This post is about being on the other side of the equation: being the source of the RFI.

I have a Raspberry Pi 4B running Open HamClock Backend. It's a very handy program that provides a wealth of useful operating information. During the Canada Day Contest last week, I noticed that whenever I transmitted on 15m at 100 watts CW, the monitor connected to the Pi 4B would go completely blank. As soon as I stopped transmitting, the display would immediately return.

Blank monitor screen.

This time, instead of being the victim of RFI from a noisy wall wart, my own RF signal was causing the problem. You could say I had become the RFI source.

It was time to investigate. My first suspicion turned out to be correct—the HDMI cable running from the Pi 4B to the monitor. I had a spare Mix 31 ferrite toroid, so I wound a few turns of the HDMI cable through it. The problem disappeared immediately. That quick fix allowed me to get back to contesting, knowing I could look into the issue more thoroughly later.

The Raspberry Pi 4B came with an HDMI cable, but I assumed it probably wasn't the highest-quality cable available. I examined it closely but couldn't find a manufacturer, model number, or even a country of origin.

Old HDMI cable

All of the USB cables in my station are made by Tripp Lite. In total, I now have seven Tripp Lite cables in service performing various tasks. I've never had an issue with any of them, and they have consistently earned an excellent reputation for quality. Based on that experience, I ordered a Tripp Lite HDMI-to-Micro-HDMI cable for the Pi 4B. Yes, I could have simply left the ferrite toroid on the original cable, but I prefer to solve a problem at its source whenever possible.

So, what makes the Tripp Lite cable better? It features excellent shielding, heavier-gauge conductors, superior overall construction, and is backed by a lifetime warranty.

New Tripp-Lite cable

When the new cable arrived, I removed the ferrite toroid from the original cable and repeated the test. As expected, transmitting on 15m caused the monitor to go blank once again. I then replaced the original cable with the new Tripp Lite cable—without using the ferrite toroid—and transmitted under the same conditions. This time, the monitor remained stable with no blanking whatsoever.

Another RFI adventure solved through a little troubleshooting and some simple testing. Sometimes the simplest solution really is the right one.