[RFI] Comcast - 80 meters rings phones

Jim Brown jim at audiosystemsgroup.com
Sun Nov 19 13:37:15 EST 2017

I agree with both of these suggestions.  CAT5 makes great telephone 
cable if you use one pair per line. The only thing I would change is to 
use even more turns on the ferrite choke(s) and I would place them close 
to the phones that are ringing.  FWIW, modern wired phones are notorious 
for RFI.  This is another problem that can often be solved or minimized 
by the use of a UHF wireless system, in this case, a base station and 
multiple "walk around" handsets. We've been using a Panasonic system for 
about five years, and another system with fewer handsets for years 
before that.

All it takes to install a system like this is to plug the base station 
into one of the wired outlets. Most are powered from the telephone line 
or a wall wart. The model we bought at Costco uses one of the handsets 
plugged into the base station for battery backup. With this RFI problem, 
I'd plug it in with as little wiring as possible to where the wired line 
enters the home and disconnect other wiring from it (doing so in manner 
that it can easily be restored). And I would put a choke one the line to 
that base station. The wall wart is probably an SMPS that will create 
RFI, so should be replaced by an old linear supply.

In doing the research for telephone chokes/filters that I incorporated 
into RFI-Ham, I obtained several popular filters that were built and 
sold by hams and measured them. The results are shown in Fig 28 on page 
19.  All of these filters are common mode chokes, and all have choking Z 
greater than 10,000 ohms across the bands they cover. One has a choking 
Z greater than 20,000 ohms on the AM BC band.

73, Jim K9YC

On 11/19/2017 9:19 AM, Dave Hachadorian wrote:
> If ALL of the phones are ringing, I suspect the Comcast box is telling them to ring.  I would try a good K9YC 80 meter choke on the phone line right where it comes out of the Comcast box.  Then I would also try one of those same chokes on the power supply going to the Comcast box.
On 11/19/2017 8:52 AM, Augie "Gus" Hansen wrote:
> Hi Steve,
> If any phones in his home have extension cables they are likely using 
> parallel wires, not twisted pair. Replacing such extensions with 
> quality UTP cable goes a long way toward curing this type of RFI.

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