Topband: Broadband RFI fix. Re: 2Wire, Inc. 3800HGV-B Gateway. RFI --Problem fixed for now….

[g3pqa at onetel.com]

When I first went over to broadband a few years ago, only 10 watts on 160m 
used to make the ADSL2 lose connection, even with a wireless system.
The house is fed with an overhead telephone line.
Of course it depends on location and systems, but after trying various 
filters for months and months I fixed it with a combination of measures as 
follows:-

1. Common mode filter in series with Telco line where it comes in house, 
just before ADSL splitter (splitter is a replacement faceplate on BT 
mastersocket)
2. Balanced LPF filter just before router/modem
3. New router/modem
4. Ferrite on DC lead

1. The common mode filter is about 30 turns of a twisted pair stripped from 
CAT-5 loosely wound on a 1 inch ferrite core (unknown u - maybe RFI 
suppression type). This really did make a difference in combination with the 
LPF. (The recommended Type 31 ferrite might be better).
2. The LPF is based on the OZ1CTK design with some small variation of 
components to optimise BB speed. Passband to 1.2MHz, 35dB attenuation on 
1.8MHz.
Speed now 3MBit/s with filter.
3. Changing modem/router also made a big difference. New router/modem (Addon 
NWAR-3670 cost £38) proved much more resistant to RFI than old one. With my 
old Dynamode modem the filters were only partly effective. I also tried 
another modem (2 year old Netgear) but it only produced a small improvement, 
even 100w with filters caused the BB to unlock sometimes.
4. Ferrite on DC lead may not be necessary (I put mine on anyway, not tested 
effect).

John