AM radio noise

[Tripoth]

OK, have a Defnity system picking up AM radio noise.
The building is a radio station, but we haven't had an issue in 5 years.
5 years ago, it was particular phones and we placed am filters at the station level and fixed the issue.
The problem is on phones on all 5 floors this time.
Have run some tests and done some troubleshooting and have isolated the calles to a specific trunk group.
This trunk group is only used for outgoing local calls.
Further troubleshooting allowed me to pinpoint 2 co lines.
The lines come into a dmarc on the 2nd floor. Wiring takes the lines to the phone room on the third floor.
I have placed an AM RF filter(Part number WAL2B on Mike Sandman) on the lines at the dmarc. Still radio noise.
Moved the filters to the CO lines right before the Co ports on the system. Still noise.

Problem is intermittent. We have had poor weather for the past week and the issue only started up again today, so I can't really say weather related.

Looking for another perspective on the issue.

Wondering if the problem can be on the Verizon end of things as it leaves the building.

 

[trvlr1]

Have you checked your grounding to make sure that is all good? Bad weather would actually improve the grounding, so you would see more issues as things dry out. As you seem to have tracked it down to 2 lines though, I would definitely have the telco look at them.

 

[ironhorse17]

Something is not grounded properly or you are getting a slight ground on the lines. Have the provider change pairs from the CO to troubleshoot.

 

[Tripoth]

Good call. Thanks guys.

These ARE ground start lines.
I went to test the lines at the dmarc and every time I removed my ground from the lines, the connection would disconnect.

Ground from the telco would be the issue!

 

[doktor]

You can add ferrite cores to all power lines to the PBX and CO lines. Since you got the problem with noise, there must have been a change in your system (or outside).
If inside: I had an issue with an electrician that rolled up the cables for the local telephone lines. These rolled cables acted like antennas. Cables were adjusted in length and the problem was soled.

///doktor

 

[Munz]

Have had a few problems with AM radio before. We used .oo68 uF caps across the loop start PSTN lines for 1368 kHZ blocking, and .01 uF when the station changed to 666 kHz AM. Seemed to be effective in most cases. However a combination of 2 of the above caps with one leg of each attached to each side of the line and the other leg of each joined and connected to earth worked in the more extreme cases.
Another problem was open ended capacitance in common with the lines that amplified the problem, and if you want to turn your phone into a brilliant radio then just common a piece of 4 wire phone cable to it and wet the unterminated end. Wait for electrolosis (sp) to form a diode on the end of the pair of unterminated wires and you're tuned in, (capacitor + diode + antenna = crystal radio). So make sure all commons are removed. A pulse echo tester (ie "Riserbond" or "Techtronics" to name just two,) can find where these commons are attached to your line quickly and easily. Probably a Telephone company thing though, unless the commons are on premises.
Longtitudinal coils may help but I've found these are only good for VLF signals. (hum)

Extra dry weather is a problem. GOOD EARTHS / GROUNDING IS ESSENTIAL.

In extreme cases ( once ) I used shielded cable grounded at only one end (PBX end) and problem solved, however this was EMF interference from medical equipment and not AM radio, but if you are inside a radio station then some of the signal may get in this way. More likely only near the transmitter.

Best of luck solving this one.

One final thing to note is,... How is the studio broadcast sent to the transmitter? Does the AM 10kHz broadcast line share a cable with the phone lines (anywhere!!)? If so look for crosstalk in the twisted pairs and then maybe seperation of the signals by placing the broadcast line in a different 10 pair unit of the external UG cable or in a seperate (discrete) internal cable, and at the least seperate by more than 25 pairs in the internal cable. That way you should eliminate crosstalk into those 2 voice telephone lines.

A split pair (absolutely anywhere) in, or near you broadcast line will cause this. Any recent work done on the lines?

Regards, Munz

 

[SYQUEST]

You might want to have the telco check the protector modules @ the cable head. That has the possibility to be a receiver of RFI, in addition to split pairs. Check and verify ALL house wiring, pairs, and bridge taps. It doesn't take much to detect AM radio...

....JIM....