WD8DSB 160 meters interference from local manufacturing facility

This website documents interference that WD8DSB is receiving on 160 meters that appears to be from a manufacturing facility that's located a half mile away. The interference does turn on and off. The interference is sometimes present a majority of a 24 hour a day but this past Sunday Nov 1, 2015 it was not present (it was back on Monday morning when I checked around 5:30am EST).

The on/off pattern was analyzed this past Saturday afternoon (Oct 31, 2015) and the pattern was as follows (approximately): 14 seconds on, 3 seconds off, 14 seconds on, 15 seconds off (and this pattern keept repeating). During the 15 second off period there is often a very brief on pulse (maybe 1 or 2 seconds long). Tuesday afternoon (Nov 3, 2015), the pattern of the interference was much different with very long periods of on time (not cycling between on and off over a short period of time).

Below is an SDR receiver screen shot showing the interference pattern, a map showing the location of the manufacturing facility relative to WD8DSB, and a link to a youtube video that shows the interference at the location of WD8DSB using an SDR receiver connected to the wideband IF output jack of a Kenwood TS-180s, and it also includes video showing the recording of the interference from within the office of the manufacturing facility using a DX-440 receiver with a 14" diameter tuned shielded loop antenna using no preamp.

Screen shot with center frequency = 1.912 MHZ using SDR receiver connected to Kenwood TS-180s wideband IF output jack.

Youtube Video Link : http://youtu.be/Ly6r6I91484

Dec 1, 2015 Update

Here is a somewhat long update on the RFI I tracked down to a local manufacturing facility a few weeks ago.

Went to the facility a week ago with portable HF receiver and portable tuned shielded loop in hand, but there was so much broadband white noise within the facility that direction finding and/or sniffing of the signal of interest was impossible (could not hear the signal of interest through the local broadband white noise). We (the owner and I) tried watching the manufacturing machines from a remote location where we could hear the interference of interest to see if we could visually match up the interference on/off sequence with machine motions, but we were not successful. Therefore I decided I had to take a more technical approach.

I went back home and designed a circuit that would log the on off status of the interference every second on my PC, and also used Audacity to continuously record receiver audio. Both of these systems were connected to my HF transceiver in my shack and they allowed unattended logging of the interference.

Using the above recording systems I was able to tell the owner of the facility today that the machine cycle time average was currently running 71 seconds, and that the machine generating the noise started back up after the Thanksgiving weekend yesterday (Monday) afternoon at approximately 12:38 pm.

The owner then looked at his historical data logging system, and immediately told me that my data matched up with his machine #18.

This afternoon we confirmed that his machine #18 was the culprit. The owner was at machine #18 while I was at my house listening real time to the interference. The machine was turned turned off and also ran some cycles which allowed us to confirm the interference patterns at my house matched up exactly with his #18 machine.

The machine is an injection molding machine (only 6 months old, with 3 more of the same machines on order), and it has a servo AC motor. I am now going to work with the owner to investigate the design, before we decide how to proceed. One of the first things I want to see is if an input line filter is part of the build, and to determine the manufacturer and model number of the drive so I can look into the manual of the drive to see if the machine builder followed the drive manufacturers recommendations for RFI compliance.

Feb 10, 2016 Update

Here is the final update on my 160 meters interference that was originating from an injection molding machine located at a manufacturing facility 0.5 miles from my house.

Last Friday a low cost 3 phase EMI filter was installed on the input side of the AC Servo Drive, and the interference that was peaking 10 dB above my noise floor on 160 meters at my house disappeared, and it can longer even be detected while sitting in the parking lot of the manufacturing facility (about 100 feet from the machine). I was hoping the low cost filter would reduce the interference by at least 10 dB, so the final results are extremely pleasing (really amazing).

Filter: Delta Electronics model 30TDVST2

Cost: ($76.29 at DigiKey)

The filter was purchased and installed by the owner of the manufacturing facility, but I did point him toward this particular model (due to current rating, cost and size) with the understanding that I was only providing some options and that he was totally responsible for any and all action taken.

The AC Servo Drive manufacturer recommended an EMI filter available out of Japan at a cost of $955. This $955 filter is the "default" filter they specify for the AC Servo Drive we were working with but it does not take into consideration that we were using the AC Servo Drive with a motor smaller in size than the max rating of the drive, nor did it take into consideration that we might be able to get away with a simpler designed filter (less attenuation, etc). Taking the low cost filter approach is what kept things moving forward.

P.S. I baked cookies and brownies last night and delivered them to the manufacturing facility this afternoon to say thanks (this is my typical approach).

Website created and maintained by Don Kirk (WD8DSB), 10/30/2015