Tuesday, July 27, 2010

I’m having problems with RFI to my neighbor’s (and my own) telephone ...

Q Erik Iddings, KF4KRK, asks, “I’m having problems with RFI to my neighbor’s (and my own) telephone. One neighbor picked me up on a 900-MHz cordless phone. She said she could not understand anything but could tell I was on the air. My mother has picked me up on a corded telephone, again nothing legible. And my other neighbor picks me up on his 49-MHz cordless.

“I operate 6-meter SSB using an ICOM IC-706 MkII with 100 W PEP. My radio and tuner are properly grounded. I even made up a coax balun at the shack entry point hoping that would solve the problem. The interference is still there.

“One of my fellow ARES members is an engineer with the
telephone company. I called her the other day and told her
about the problem. She had the customer service manager and a line technician come out and install an RF suppresser on one neighbor’s incoming line. That didn’t work. 

“I’m about to go out of my mind trying to figure this out. Unless I can get this RFI problem resolved, it looks like I’m going to have to give up operating on 6 meters unless all the neighbors are at work!” 

A Start with the premise that the FCC rules require that spurious emissions (signals outside the ham bands) not cause interference with other radio services. This is your sole regulatory responsibility.

Now, those 900 MHz and 49 MHz cordless phones are regulated by Part 15. Part 15 says that these devices must not cause harmful interference and are not protected from interference from licensed users. The FCC’s material on interference also adds that non-radio devices (telephones, alarm systems, etc) that experience interference are “improperly functioning” as radio receivers. Although you may want to help your neighbors resolve these problems, the rules may help you put that into perspective. For RFI that is not caused by a rules violation, your help is simply neighborly and you should see yourself as a locator of solutions, not a provider of solutions. 

For general info about RFI, info for your neighbor, info on telephone interference, info on Part 15, see http://www.arrl.org/tis/ and follow the TISPAGES and RFI links.

I will add that you can sometimes correct problems with cordless phones by filtering the base unit. Get a RadioShack telephone interference filter for the line and a Palomar F-140-43 ferrite core for the power supply lead (wind about 5 turns or so). If this doesn’t work, it is the RF end of the phone being overloaded. For the 49 MHz phone, it is rare that base-unit filtering works to suppress interference from a 6-meter signal. The wireless phones or their owner’s manuals should have a label that indicates that they are not protected from interference.

From QST August 2000