On Sun, 27 Feb 2011, Jim Brown wrote:
> Gordon noted that common mode chokes are only effective if near the STB
> (set top box). This strongly suggests that the STB is the weak link. If
> the common mode choke makes a big dent in the RFI, I'd bet the major
> component of the coupling is something as simple as a Pin One Problem in
> the STB. The Pin One Problem is discussed in the RFI tutorial,
> previously cited. Now, that does NOT mean that there couldn't be other
> means of ingress -- poor balance of the input circuit for the balanced
> cable, poor strongly signal handling of that input stage, poor shielding
> of the STB, or even ingress somewhere else in the system. The nature of
> Pin One Problems is that they tend to be quite severe, so fixing them
> makes the biggest dent. But once you've killed them, the other coupling
> routes are still there, usually at a lower level.
> 73, Jim Brown K9YC
One of the primary ingress points is the house wiring, and if present
arial drop. Placing a choke at modem ingress puts it between the antenna
and the modem. Placing at NID puts it between the primary antenna and the
Backfeed to the CO is possible, but we are talking about a path with 20db
loss minimum here, the modem is the critical point to protect.
I would however say "much more effective", instead of "only effective".
RFI mailing list