sundance-communications.com/forum Forums General General Telephone & Systems Information RFI on 4 line phones

Living near 2 hi power radio stas. I have a problem with RFI on 4 Line phones. RCA latest ones. No filters seem to do any good. Almost seems like the handset is picking up the RFI.
Any comments. I have Mike Sandman's paper on the subject, but cant get rid of it.???

Do any of the surronding people have the same problem ?

It could be one phone letting the rfi in the lines remove all phones and one by one hook them back up until the interfance happens....this be the bad phone


Hope this helps

Also house wiring.

Took out a Merlin about 1/4 mile from a radio station --- sounded like he had MOH ALL the time.

Rewired with shielded and grounded wiring --- new system --- now has no MOH.

KLD

I have a similar problem at a local airport. There are two customers involved. One has a small Executone system. Mike Sandman's filters cleared 99% of the problem on the Executone. The other customer has 4 line TMC SOHO sets. I've tried filters at the demarc, on the mounting cords, and on the receiver cords. I've also disconnected any unused jacks and grounded the spare pairs. I pretty much followed Sandman's chart. Nothing helped the 4 line sets. The County finally relocated a couple of small transmitters to another location in the building. That cleared most of the problem. The interference still happens when a plane transmits in close proximity to this location. You don't have the luxury of moving the transmitters. I guess what I'm saying is that I haven't had much luck with filters on the 4 line phones. They seem to act like more of an antenna than a system.

Are these AM broadcast stations? They are usually the worst offenders. Usually consumer grade phones like those are made so cheap you know they are going to skimp on RF rejection. "How many times does this happen so why should we spend the money" is the philosophy.

Do consumer type single line phones have this problem? What about a 2500 style non-electronic phone?

Maybe you need a 1A2 at that location. :thumb:

I would also find out what other people in the area use. If telephone operation is generally not possible no matter what you use because of the RF I think you may have a case against the transmitters.

-Hal

I am pretty sure that most, if not all 4-line phone "systems" use FM frequencies superimposed on line 1 for intercom and signaling (DSS/BLF). This would lead me to believe that RFI of any kind might be a problem. An RFI filter for all four pairs at each station seems like a costly solution, however it would bring the cost of the system more in-line with the cost of a "real" digital system that would be less succeptible.

Thanks for the plug, Hal for 1A2, but with all of those relay coils, ringer coils, even coils in the older dials (transformers), it would be a nightmare in a strong AM environment! I will take your statement as humor!

Dunno about that. I remember several radio stations that had 1A2's with no problem. When one upgraded to the Merlin it was a disaster.

Only way to be sure is to try it but I think the old electro-mechanical stuff is lots less prone to this than modern equipment with amplifiers, electret mics and other electronics.

-Hal

If Sandman RF filters don't work try a ferrit choke on the line and/or handset cord. Sometimes its the harmonics that cause interference. The worst case of RF I had was a church about 50' from a 100Kwatt FM tower. Just 20' of zip cord on speaker would pickup signal.

Shielded wire solved the problem in San Bernardino for a cycle parts shop. The old Tie Ultracom just sucked up the radio station with regular cable.

Three pairs for the phone, 4th pair grounded on both ends, short line cords, it worked.

Had a site with a TIE 2056 system that could pickup a country radio station.
Problem was the owner hated the Oak Ridge Boys.
The funny thing was....If you held the handset to your ear and moved the handset cord to your right or left the station came in loud and clear.
After several attempts (and several mounths) to fix the problem, The customer moved out out the building.
So my advice is to offer your customer a great discount on moving their system.