Topband: Help with RFI

[Jim Brown]

On 1/13/2013 5:08 AM, Brian Machesney wrote:
> Wrapping everything in ferrite did not solve my 160m RFI problems. OZ7C
> provided a filter circuit that I use successfully:

Let's define the problem.  Interference to DSL is VERY different from 
interference to Ethernet. I agree with Pete that using wireless Ethernet 
for as much as practical of a system is a good thing, and I've been 
doing that since moving to CA seven years ago.  My internet is CATV, so 
I've not had to tackle DSL myself.

The problem with interference to DSL is that 160M is within the heart of 
the range of DSL signals, and both the equipment and the wiring are 
poorly designed to reject them.  In the old days, all telco wiring was 
twisted pair, but in the last few decades it has been mostly downgraded 
to parallel conductors, and this has had a huge impact on RFI, noise, 
and crosstalk in difficult situations. There is also the issue of 
equipment poorly designed to reject the interference, or to switch to a 
lower bandwidth mode when interference is present.

The issue of RFI to DSL has been worked through in considerable detail 
on the RFI email reflector, and the consensus is to first challenge the 
DSL vendor to fix it.  A low pass filter for the telco line is also a 
good move, and so are replacing as much as practical of telco wiring 
with good twisted pair, like CAT5/6/7, and adding a serious common mode 
choke to the cables going to the modem.

73, Jim K9YC