Adventures in RFI
RFI? In my shack? - It’s more likely than you think.⌗
RFI is something I was introduced to very early on while operating end-fed antennas.
Why is my USB connection to the radio dropping as soon as it goes into TX? RFI
Why does my waterfall just display noise when I connect it to USB? RFI
Why does my noise floor jump to S9 when a new appliance arrives in the house? RFI!
Ok, so how do we solve this problem? Suppression with Ferrites!
In some scenarios it’s easy to identify the source of the problem…
Did something just get plugged in?
Did something just turn on?
Bingo! You found it.
Throw an appropriately sized ferrite on it and move on with life.
If the source of the noise is not apparent it’s critical to be methodical and scientific to reliably detect and suppress it. Learn from my mistakes. It may be emitting from something you control in your own home or something external.
Case Study⌗
A challenger approaches…⌗
I recently brought a new appliance into my home, a Samsung Refrigerator. It brought with it two different types of ice, a neat auto-refilling water pitcher, and S9 noise on bands 20m-10m. I knew something was wrong but not how to effectively resolve. How do I stop something from making noise when all I can see is the power cord? Do I lose access to operate my favorite HF bands from home for the foreseeable future or void a warranty?
I quickly determined access to those bands had more value than the non-returnable refrigerator now sitting in my kitchen. Let’s see what we can do…
Plan A - Seek an accepted solution.⌗
With little experience in this area I turned to searching the internet. This turned up a reddit post referencing the specific brand, some steps already taken and a potential solution.
Perfect. Lets give it a shot.
I selected a comparable part that would fit my new source of noise, a SCHURTER INC / 5500.2044.
Once installed the noise dropped but it wasn’t completely gone… ruh roh.
Plan B - Flounder.⌗
Enlisting the help of my trusty Elecraft Kx2 and a small HT antenna I attempted to locate what parts of the fridge were actually radiating. Using the Kx2 much like a metal detecting wand, I quickly determined most of the noise was emitting from the door and the rear panel. Anywhere in the vicinity of the fridge the Kx2 registered S5 noise. Not great, not terrible.
Ok, what do we do? Ferrite anything we can reach.
Ferrites on the cables leaving the control board.
Ferrites on the cables leading to the door.
With this step completed the Kx2 no longer had a registration on the S-meter when near the fridge! Progress! Let’s check the main QTH antenna…still S5.
At this point I doubted the fridge was involved. Time to try something else.
Plan C - Cut the power.⌗
To figure out where this noise was really coming from I powered down everything in the house and flipped the main service breaker. Remember when I said we needed to be scientific? Now’s the time.
“Remember kids, the only difference between Science and screwing around is writing it down.” -Adam Savage
With these words of wisdom in mind lets write it down:
| Band | Noise Level |
|---|---|
| 10m | S1 to S2 |
| 15m | S1 to S2 |
| 17m | S3 (?) |
| 20m | S4 (!) |
| 30m | S1 to S2 |
| 40m | S2 to S3 |
Our noise floor was higher than we realized on 17 and 20 but there is room for improvement on all bands.
Flipping breakers on one-by-one and checking the waterfall and S meter I located multiple sources of noise:
- Apple AirPort Express. Disconnected…
- Google Chromecast USB power supply. Trashed…
- Bedside table USB charge port. Trashed…
- No-name USB charger used to power my Meshtastic node. Tuh-rashed!
Once power was completely restored I noted readings on all bands were very close to the readings when the power was completely removed! Perfect!
The HVAC air handler and outdoor compressor added some noise but not enough to warrant touching them.
Success.⌗
So, we solved our noise problems but what did we learn?
- It’s important to know your local noise level.
Without these base readings you may waste time attempting to solve problems outside your control. - It’s important to be methodical.
Formulate a plan, enact the plan then evaluate results.
This is the quickest way to success.
Resources⌗
Here’s some resources I reviewed during this whole process.
I hope they also help you.