[UK-CONTEST] re ADSL Modem RFI

[Steve Wilson, G3VMW]

In message <mailman.25.1258401607.26269.uk-contest at contesting.com>, 
uk-contest-request at contesting.com writes
>Message: 2
>Date: Mon, 16 Nov 2009 09:26:05 -0000
>From: "Chris Tran GM3WOJ" <zl1ct1 at gm7v.com>
>Subject: Re: [UK-CONTEST] ADSL modem RFI - thanks
>To: <uk-contest at contesting.com>
>Message-ID: <010301ca669e$d7504b70$6601a8c0 at sempron>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>       reply-type=original
>
>Thanks everyone for the very helpful advice, suggestions, circuits and
>links, both on and off reflector. (The several 'reduce power' suggestions
>were not so helpful, hi)
>
>Our wired phone system is ancient and mostly redundant cos we use a DECT
>phone 99% of the time - it is so old that there is no BT 'master socket'
>which baffled the BT Openworld installer in August when he came to check our
>line. The ringer wire is not connected anywhere.
>
>About 50W on 1.8MHz is enough to cause problems, so I'll get a new-style
>faceplate fitted with only one phone and the ADSL router connected to it,
>remove all the redundant wiring, then try some filtering.
>
>73
>Chris   GM3WOJ/ZL1CT

Chris,

I've been following the very helpful discussion on here about ADSL modem 
RFI because I've had much the same problems as you are describing. The 
BT lines feeding our house are entirely overhead and there's about 35m 
of OH wire from the house to the telegraph pole in the street.

Here I use a Netgear DG834GT router, which normally syncs up at around 
4.2M, but 50-100W on any band below 20m instantly disconnects the router 
I think because of RF picked up on the OH BT line. I have a KY Filter in 
line and the lead from the DG834 router that connects to the BT socket 
is wrapped on a huge ferrite. Neither really helped.

Like you, we use DECT phones and there was no BT NTE5 'master socket' 
fitted as the house is about 40 years old now.

Today, I've fitted an NTE5 master socket where the telephone line comes 
into the house (upstairs bedroom) and fitted an ADSL filtered face plate 
like the one that G3ZVW recommended in his post on here. This is the one 
I used:

http://www.adslnation.com/products/xte2005.php

The filtered face plate has two Krone connectors - one for telephones 
and a straight-through one for ADSL extensions. I wired the shack 
telephone socket from the ADSL connector and the other telephone sockets 
from the filtered connection. This helped, but didn't clear the problem.

The real improvement came when I built the OZ7C filter as recommended by 
Jan G0IVZ and Andy ZC4VJ. I didn't have any 6.8uH chokes, so I wound 
some (35 turns on a T50-2 toroid). Putting this filter in line with the 
router near to the telephone socket did the business. No more router 
disconnection at full power on any band. There is a slight degradation 
of S/N ratio on 160m and 40m (but not 80m), but the router stays 
synchronised and the connection holds. There is about 1dB of insertion 
loss attributable to the filter, but I'd rather have slightly slower 
ADSL sync speeds than frequent disconnects.

There's some more ideas about the OZ7C filter here (in French):

http://ed64.ref-union.org/technique_fichiers/Filtre_ADSL.pdf

I was considering getting a broadband wireless dongle to connect to the 
mobile network, but this has saved me going down that route. There may 
be some more options like common-mode chokes that should also help, but 
for now things are looking a bit better.

73

-- 
Steve Wilson, G3VMW
Bramham, Wetherby, West Yorkshire