[RFI] DSL Filter Update

Christopher E. Brown cbrown at woods.net
Sun Mar 8 18:43:14 PDT 2009

On Sun, 8 Mar 2009, Jim Brown wrote:

> On Sun, 8 Mar 2009 18:05:38 -0500 (CDT), Christopher E. Brown wrote:
>> A filter with a sharp cutoff starting around 3Mhz combined with heavy
>> common mode choke would have alot less impact on the sync rate.
> That's sort of the direction I was thinking about. Note that one can get
> quite serious with a common mode choke without affecting the
> differential mode circuit at all. Thanks for the info re: 2.2 MHz max
> bandwidth. The engineer friend I consulted on this told me 1.1 MHz.
> Sharp guy, but his experience in that industry was at least 4-5 years
> old, and he's been doing completely different things since.
> 73,
> Jim Brown K9YC

Depends on the DSL gear, ADSL1 cuts off around 1.1, VHDSL uses much higher 

Common use these days in the US is ADSL2+, with ADSL1 hardware cycling out 
of production.

Also, remember that RF can impact *BOTH* ends.  I have seen a couple cases 
where enough signal made it into the line to impact both the CPE *and* the 
DSLAM, as well as causing increased error rates for neighbors in the same 
cable bundle.  A serious common mode choke at both the CPE and at the NID 
could be needed in severe cases.  At my home I have chokes at both ends of 
the line, only a single cylinder but my original DSL issues were not so 

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