Partner ACS and AM radio interference

[jlshelton]

I'm trying to debug some Radio interference problems with an ACS installation located < 1 mile from KNBR AM radio transmitter. Former Merlin system required AM filters on the CO lines just before entering control unit, and still got some mild AM radio sound when long (50 ft) handset cords were fully extended. Otherwise, was fine.

Now, with Partner, accessories get bad AM radio. On the plus side, I can listen to a ball game while talking on the phone. But most of the time, that's not desirable.

The obvious thing to try is adding AM radio filter between the Partner phone and the accessory (headset in this case.) It helps some, but not enough. On another phone, it is of no help at all.

For those who haven't had to deal with radio interference, it's a nuisance, but should be solvable scientifically. AM radio enters system almost anywhere, particularly on unshielded, untwisted long runs of wire. A component in the system (handset, base telephone, corroded connection, etc.) acts as a &quot;detector&quot; (cheap radio) and converts AM signal (which is abou 700 kHz) into audio signal. Once converted to audio, you cannot filter it. The correct solution is to put RF filters as close to the detector as possible, and between the detector and the wire acting as an antenna.

Puzzle: Since Partner sets have no AM radio sound themselves, I assumed that they were not the detector. The headset amplifiers are likely candidates, so I put filters just before them. But no success. Is it possible that the Partner phone itself acts as a detector, but only for the signal it sends on to the AUX jack?

If that's true, then I need an AM radio filter just before the Partner phone. But these phones have 4-wire connection. Most AM filters only connect pair 1 through a filter, and often just ignore pair 2. Has anyone tried 2-line AM filters? Do they interfere with the signals on the second pair?

Thanks in advance.

 

[bobsou]

try put the filters just on the first pair as the second pair is for the button & lights

 

[392]

No doubt, the only thing that allows RF to pass is improper grounding somewhere in the system. The cause is that something is acting as an ungrounded antenna.

Verify - absolutely - the system is grounded to a true earth ground. If you're using a TowerMax, be sure to wire the CPU ground screw to the top hole on the CO protector. If you're using a straight surge protector, ground the CPU screw to the ground lead the CO line lightning protectors are using. A UPS is good for isolation, as well. Be sure the electric system ground is a true ground, not just run to building steel, but to a copper ground rod.

If all is grounded properly, you can still get RF through bad station cabling. If this is the case, you should be able to wrap the handset cord a few times around your forearm and the RF will fade away. For that, you need a choke. ACSs come with an SMDR port choke, you can use that to verify. It's a small, square, latched plastic box filled with two metal halves that form a square donut when latched shut. Loop the line or handset cord (whichever works best) through the choke 3-4 times to squelch the RF.

Don't waste your money on the filters, they don't work except in rare instances of welding shops and such. The reason the headsets are suspect is because they have amplifiers built in to strengthen the RF introduced elsewhere and converted to audio. The key is to shunt the RF to ground before the conversion occurs.

Good luck. I chased RF in a metal building under a 50,000 watt clear channel AM transmitter for 3 months. The key is: ground everything!

 

[itpphoneguy]

Hi jlshelton,
392 is right on. If you find station ports on quad, use the quad as a pull string. I have found CAT-5 to be the best to run the Partner on. Watch out for ground loops! You want a star ground, ie everything to one point at the system ground.
As far as the detector, any semiconductor will work as a detector. Try putting a small value cap across the first pair in the jack if you can't solve this any other way (about 0.001 - 0.01uF). This would be near the phone end.
Good luck with this,
-Chris

 

[jlshelton]

&quot;392&quot; offers some good points.

My system is well grounded. Per older AT&T instructions, I have a &quot;bonded&quot; ground wire (AWG 12) running in parallel with the CO lines from the equipment room to the outdoor service entry, and from there through the SBC protector device into a standard copper ground rod.

How do I ground anything beyond the ACS processor? You can't ground any lead in a T/R device.

The standard RF Filters available at Radio Shack and other telephone accessory departments are useless with AM because they typically are tuned for 3.0 - 30 mHz. I get true AM filters (300 kHz - 3.0 mHz) from Sandman. They have worked well for me, blocking the AM radio coming in on the CO lines.

All station lines are CAT-5, thus giving me good protection via tight twists. I use CAT-5 patch cables from the wall to each set.

This close to the transmitter tower, *everything* is an AM antenna, including my body. I can increase radio volume on the headset just by reaching for the amplifier volume control. It's possible that the headset cord itself is an antenna. But, what's unusual is that the same headsets worked well on the old Merlin system. So, I suspect something up with the Partner phone acting as a detector.

I just found, a few minutes ago, some DSL filters that pass both pairs 1 & 2 (perhaps filtering both.) Since the DSL filter is a low-pass filter tuned for about 300 kHz, it too works pretty well with AM radio suppression.

More experimentation required.

 

[itpphoneguy]

Hi jlshelton,
I intended the co filters to be grounded, not the station side. Try the caps on the voice pair in the jack.
-Chris

 

[jinxs]

We had the same issue in a plant with an ext that extened over 100'. What we did to correct the problem was to run shielded cable and bond the shield to the same ground as the ACS and then add an RF filter at the phone end. No mo RF. Then again, running shielded cable is costly, how bad do you need this issue resolved?