[RFI] 160 Meters Interference Tracked Down To Local Manufacturing Facility

[Jim Brown]

Congratulations on a fine job of engineering!  One of things I learned 
early on was that good engineering is doing enough to solve the problem, 
not enough to gold plate it. :)

73, Jim K9YC

On Wed,2/10/2016 12:03 PM, Don Kirk wrote:
> 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).
>
> 73,
> Don (wd8dsb)
>
>
>
> On Tue, Dec 1, 2015 at 6:20 PM, Don Kirk <wd8dsb at gmail.com> wrote:
>
>> 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.
>>
>> Just FYI,
>> Don (wd8dsb)
>>
>> On Fri, Oct 30, 2015 at 7:48 AM, Don Kirk <wd8dsb at gmail.com> wrote:
>>
>>> Thought I would share my latest RFI issue that I tracked down yesterday
>>> to a local manufacturing facility located 0.5 miles from my QTH.  Below is
>>> a link to a website that documents the interference, and it includes a link
>>> to a youtube video that has recordings of the interference from my shack as
>>> well as from within the office area of the manufacturing facility.
>>>
>>> I will now work with the facility manager to track down the actual source
>>> of the interference.  Turns out that I am actually an old customer of this
>>> facility through my daytime job (very small world).
>>>
>>> website link http://sites.google.com/site/rfimetro/
>>>
>>> Stay tuned to find out the actual source.
>>>
>>> 73,
>>> Don Kirk (wd8dsb)
>>>
>>
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