Equipment (Modems,Gateways)
Modems, Gateways, and Networking Devices
Male IT Specialist Holds Laptop and Discusses Work with Female Server Technician. They're Standing in Data Center, Rack Server Cabinet is Open.

Electromagnetic Interference / Radio Frequency Interference (EMI / RFI) causing internet loss.

Ok, I'd figured I give this dilemma a shot here since such high quality responses here.  I am not expecting a solution or answer here given the non-typical topic, and I may have to consult a specialized forum etc about this... but giving it a shot anyways in case anyone has run across this type of problem.


My company uses specialized equipment that incorporates something to the nature of neon transformers inside the device, in and around office nearby the server room and all client pc's etc.  Luckily, we haven't had any data corruption or anythign like that over the past 15 years this way.  We cannot currently isolate everything.  The device(s) state HIGH VOLTAGE, SECONDARY 4000 V / 50MA PRIMARY 115V 60CY (I assume 60Hz?)  Can adjust dial from 0 to 120 VOLTS.  Plugged in and grounded.  It puts out EMI/RFI when on.  It definitly interferes with FM radio here, old type CRT televisions, and old telephones lines and telephone line connection to security system (sounds like bad static)....but not newer computer equipment...except for the router or switch now.


Facilities that have welding machines nearby I would expect have this problem also, probably even more so.  I definitly know welding machines cause intereference with graphics tablets as those use radio frequency to transmit data from the tablet to the pen.  Cause bad jitter and erratic movement.


But the problem I am now having is when these high voltage devices are powered on and put in use, every so often it is interfering somehow with the router and causing loss of the internet.  i.e. Network Internet Access icon shows no internet, and obviously no internet via browsers etc.


The cable modem/router is a DCP3939B.  port 1 goes to the Trendnet TEG-S80g 8 port switch which goes out to the client pc's throughout the office via CAT5e.  the other 3 router ports are empty. (new CAT6 small length cables used to connect switch to the junction block, junction block out to ethernet wall plates use cat5e).

The lights on the modem/router go out.  So does the both lights on the switch. (top green light for LINK/ACT, bottom green light for 100/1000Mbps when working)  the rest of the ports on the switch stay active and working.  Sometimes when the green lights go out, sometimes they may turn yellow first etc.  Not sure if the interference is being inducted through the ethernet connection points or the swith or the mode/router itself?  or even the power cables of the router/switch etc?


Everything is on a good high quality/capacity battery backup and surge suppression and EMI/RFI filtration.


I am not sure, but possibly the Switch could be the problem..reason I say this is before I had this problem, I had my main PC directly connected to the ethernet wall jacks in the office then direct to the modem/router port 1 BYPASSING the switch in the server closet.  basically the switch and server were not part of this equation.  Just the modem/router and the ethernet wiring throughout the office walls/attic etc.


So I am not sure if the switch is causing the drop in the internet, or if something else is connected to the modem/router that is.  If it is the switch...maybe there are soem high quality switch options that do betetr against interference?  I.e. hospitals that have MRI, catscan, xray machines etc etc etc, what do they use against interference?


I don't know if there is any way to shield these things or what.  I used to have this problem with a older computer nearby, replaced with a much newer higher quality computer (and high quality powers supply etc) and no problems since then.  But now that I am networking many pcs, server, switch etc, I have this new problem witht he modem/router dropping internet connection.


Maybe I can just enclose the entire server closet in a LEAD BOX?  or the devices causing the interference in a LEAD BOX? just kidding, not feasible.


Thanks for any help...even if possible.  : /

0 Kudos
Trusted Forum Contributor

Re: Electromagnetic Interference / Radio Frequency Interference (EMI / RFI) causing internet loss.

Hello again timd1971,


I have provided you with some direct EMI Reference Information from the DPC3939B User Manual below that you may want to peruse for your information. This is an issue that we all face but, according to your data center description you are more impacted than the general residential or business customer for the obvious reasons in your post. I know this does not provide you with the Emag Engineering technical detail you were likely looking for, however,  I would like to make sure your DPC3939B settings are maximized for consistent functional operation. 


You should make sure that your DPC3939B WAN and LAN segments have the DNS primary= and secondary= programmed correctly. Unless you are using some specific DNS settings for your specific business networking requirements. It is also a good configuration practice to make sure your LAN Leasetime = Forever. These both can be configured by you from a directly connected Ethernet computer/laptop interconnected to any Lanport 1-4 on the rear of the DPC3939B, then bring up a browser and entering in the address field, when the user interface log screen comes up use username=cusadmin and password=highspeed. The click on Connection and select WAN or LAN to make the above configurations I have specified.


Hope this helps you out. 


EMI Reference Information from the DPC3939B User Manual:


United States FCC Compliance
This device has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against such interference in a residential installation. This equipment generates, uses, and can radiate radio frequency energy. If not installed and used in accordance with the instructions, it may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment OFF and ON, the user is encouraged to try to correct the interference by one or more of the following measures:
 Reorient or relocate the receiving antenna.
 Increase the separation between the equipment and receiver.
 Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
 Consult the service provider or an experienced radio/television technician for help.
Any changes or modifications not expressly approved by Cisco Systems, Inc., could void the user's authority to operate the equipment.
The information shown in the FCC Declaration of Conformity paragraph below is a requirement of the FCC and is intended to supply you with information regarding the FCC approval of this device. The phone numbers listed are for FCC-related questions only and not intended for questions regarding the connection or operation for this device. Please contact your service provider for any questions you may have regarding the operation or installation of this device. Declaration of Conformity


This device complies with Part 15 of FCC Rules. Operation is subject to the following two conditions: 1) the device may not cause harmful interference, and 2) the device must accept any interference received, including interference that may cause undesired operation.
Residential Gateway Model(s): DPC3939 Manufactured by: Cisco Systems, Inc. 5030 Sugarloaf Parkway Lawrenceville, Georgia 30044 USA


Canada EMI Regulation
This Class B digital apparatus complies with Canadian ICES-003.
Cet appareil numérique de la class B est conforme à la norme NMB-003 du Canada.
United States FCC Compliance
x ii OL-29163-01
RF Exposure Statements


Note: This transmitter must not be co-located or operated in conjunction with any other antenna or transmitter. This equipment should be installed and operated with a minimum distance of 7.9 inches (20 cm) between the radiator and your body. For products available in the USA/Canada market, only channels 1-11 can be operated. The selection of other channels is not possible.


This system has been evaluated for RF exposure for humans in reference to ANSI C 95.1 (American National Standards Institute) limits. The evaluation was based in accordance with FCC OET Bulletin 65C rev 01.01 in compliance with Part 2.1091 and Part 15.27. The minimum separation distance from the antenna to general bystander is 7.9 inches (20 cm) to maintain compliance.

This system has been evaluated for RF exposure for humans in reference to Canada Health Code 6 (2009) limits. The evaluation was based on evaluation per RSS-102 Rev 4. The minimum separation distance from the antenna to general bystander is 7.9 inches (20 cm) to maintain compliance.







Re: Electromagnetic Interference / Radio Frequency Interference (EMI / RFI) causing internet loss.

ALl my ethernet cables are CAT6 and was assumed whn purchased they were they BEST and probably SHIELED.  No.  Not the case, even when buying CAT6 from Homedepot, Staples, Bets Buy etc, they are tjust run of the mill cheapie (but they charge a lot for them) UTP (UNshielded Twisted pair).


SO apparently my network cabling in the office also has UTP throughout.


The data communication has always been fine, no data corruption etc this way.  But ONLY the internet conenction would drop.


I replaced just 1 cable going from DCP3939B to the switch with a cable I had that is ONLY FTP (Foil Twisted Pair) and it hasn;t dropped conneciton since.  I am going to replace all the patch cables with SSTP (they have STP also), but might as well get CAT7 SSTP for peace of mind.  SSTP has BOTH FOIL shielding around each twsit, and a braided shield of the bundle.


Thsi has been a real mystery to figure out...EMI / RFI is very problematic.  UTP is fine for almost all situations, but not in my case...  my situation is like a factory or harsh noisy environment.


I just wish I knew why is a router so easily knocked out using UTP, when the entire network has no problem commuincating, transferring files without problem in the middle of the noisy environment.


Are internet routers just MUCH more sensitive to this?  Or maybe do not use good engineering to avoid EMI / RFI as much as possible. i.e. ferrite cores etc inside the router.  I even have good UPS battery back up with EMI /RFI filtering on each device and server and network etc etc.


Would think the PATCH panel would be affected also, but it isn't .  JUST affects the conenction from comcast router to switch if I use a UTP cable, the FTP cable works.

0 Kudos