RFI problem, IBM Type 1 cabling?

[dodeesos]

Hi!

One of the networks I manage we have problems with RFI (radio interference). As it seems our network generates RFI around for example 100 Mhz.
We dont have problems with the network traffic it self, but a nearby police station complains about interference in their cars when they pass our office building.
I have done som troubleshooting and narrowed it down to the cabling (ibm type 1) and/or the ethernetbaluns we use to run ethernet 100 mbps over the ibm cabling.

Before we rip out all of our old ibm cables and invest in a new cat6 network it would be interesting to hear if anyone else have come across this and maybe if there is another way (cheeper) to solve this?

This is our typical setup.
switch (cisco 2950)
|
| (Cat5e utp patch)
|
balun
|
| (IBM Type 1)
|
balun
|
| (Cat5e utp patch)
|
host (100Mbps/full duplex)

Help!

 

[wires]

I have done som troubleshooting and narrowed it down to the cabling (ibm type 1) and/or the ethernetbaluns we use to run ethernet 100 mbps over the ibm cabling."

What sort of troubleshooting made you come to this conclusion? If installed correctly type 1 being a shielded cable should be less likely to propagate RFI than UTP like cat5.

Be sure the shield on the type 1 are grounded correctly at one end only, usually in the wiring closet

BTW - 100 Mbps and 100 MHz have NOTHING to do with each other. If you are finding interference at 100 MHz then it is not likely originating in a 100Base-TX network since the fundamental frequency maxes out at 31.25 MHz.

en.wikipedia.org/wiki/Fast_Ethernet

http://www.industrialethernetu.com/courses/103_3.htm

 

[SYQUEST]

Does the Main Building Ground to the wiring closet meet NEC requirements?

....JIM....

 

[dodeesos]

The "troubleshooting" have been walkin around with a hand scanner (police radio scanner). The RFI sounds like a high pitch tone, so it is quite simple to hear it.
When I disconnect all cat5e cables from their baluns the interference stops...
I only picked 100 MHz because its a round figure and its near the problem area ~75 Mhz (Police) and 88-108 MHz (ordinary FM-Radio). According to our test we have RFI all the way from 20 Mhz up to 200 Mhz, maybe more. That aprox the range of my scanner.

Regarding grounding, I guess it done according to standards. We at least have the papers...

 

[mikeydidit]

I think wires may have you in the right direction. I would check the patch panel your Type 1 is terminated in and make sure the panel is grounded. The shielding on the type 1 should be grounded properly and you wont have any problems. You should have a grounding bar in the equipment that goes to an "Approved" ground. This would "NOT" be building steel as the grounding source.

Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison

For the best response to a question, read faq690-6594

 

[wires]

When I disconnect all cat5e cables from their baluns the interference stops..."

What make and model of baluns?

What happens if you disconnect for balun from the type 1 and leave the cat5 connected?

 

[Deweyhumbolt]

The problem is the baluns. Invest in a CAT 6 network and your/police problems are over.

Adversity is Opportunity

 

[dodeesos]

The problem is the baluns" & "What happens if you disconnect for balun from the type 1 and leave the cat5 connected?"

I have tested with two baluns connected directly (no type 1) to each other and I still get RFI. So you are right, the problem is the baluns. As it seems the network speed also is an issue, if i lower it to 10 Mbps/Half duplex the baluns stops transmitting..

We use AMP-baluns (556904-1) and another that marked "AMP 4991" on the data sheet.

Anyone with tips on any other make/modell that might handle 100 Mbps better?

 

[mikeydidit]

http://www.tycoelectronics.com/customersupport/support.asp

Above is the technical support group numbers for Tyco Electronics (AMP). I would give them a call and see what they recommend. I have seen some connectors for the TYPE I cables that have a Cat5 RJ-45 connector. That may be what they recommend.

Hell, there are no rules here - we're trying to accomplish something.
Thomas A. Edison

For the best response to a question, read faq690-6594

 

[wires]

Like Mike says - Call Tyco!

The part numbers appear to not be current. Here is the page with the current part numbers 558420-1 and 558421-1:

http://www.ampnetconnect.com/product_groups.asp?grp_id=1801&path=0,1687,1747

Hopefully this will be covered by their 25 year warranty.

 

[buitenhek]

Did the baluns come with a grounding strap?

Regards
Peter Buitenhek
ProfitDeveloper.com

 

[dodeesos]

I havent called Tyco , however I've contacted the person who leed the project to install the network some 15 years ago. He has changed employer two times sence then, I was in high school at the time.
He was able to get me in contact with a technican who might be able to help us. We will get some new baluns for testing, probably 558421-1's (The same "wires" recommended).

No grounding strap....

I will test the new baluns when I get them and post the results here.

Thanks so far!

 

[buitenhek]

The balun (150 ohm - 100 ohm) is shielded and the cable has foil and a drain wire. Does the balun complete the ground or do you have a ground loop created by the near frame-cable-far frame?

Since your test concluded higher freq interference (RFI)rather than low level EMI, my guess is your cable is a nice antenna.
Can you hear me now?

Slow calculated steps to isolate interference. The Type 1 cable should still be good.

Regards
Peter Buitenhek
ProfitDeveloper.com

 

[oldtimerbob]

You also stated that you are using the Cat5 adaptors,the problem may also be at those points since you did not say that the Cat5 was shielded.

Type One was used for token ring applications (like the old 'thinnet was' but before 'Apple talk') they came up with the adaptors for the Cat5 Ethernet applications to run over the same cable at the time to save cost of converting the cabling to all Cat5 on the premise wiring.
(no more CAU's or MAU's to contend with).

Now that the Cat5 (and faster types such as Cat5e,E,Cat6,etc are out) and in common use, the type One is harder to find and support ( Tyco is the only place that still carries any type One items ) and you won't find any contractors that will certify it any longer.

The good part about type One is that you can go longer distances than with Cat5,etc, but at a much lower transmission rate (10 mps). It is more bulky than Cat5 and takes up more area on the trays,runs etc.

Your best bet would be to up grade the cabling to all Cat5 and where needed put in an IDF due to any distance constrants.
Good Luck,
Robert

Has been in the cabling business for about twenty years and is now the Sr PM for a cabling company located in the Los Angeles area.

http://www.globusinc.net

Also a General Class Amatuer Radio Operator.