[RFI] Fw: Topband: 160m & DSL incompatibility MORE SUCCESS!
daves_shack at tiscali.co.uk
Fri Oct 28 05:26:25 EDT 2005
THIS SUBJECT AND POSTING WAS ORIGINALLY DISCUSSED ON THE TOPBAND REFLECTOR.
I THOUGH IT WOULD BE APPROPRIATE TO POST IT HERE ALSO FOR THOSE WHO MAY NOT
SUBSCRIBE TO TOPBAND BUT MAY HAVE AN INTEREST.
----- Original Message -----
From: "Dave_G4GED" <daves_shack at tiscali.co.uk>
To: <topband at contesting.com>
Sent: Friday, October 28, 2005 10:21 AM
Subject: Fw: Topband: 160m & DSL incompatibility MORE SUCCESS!
> HI GUYS!
> THERE 'S BEEN SUCH A LOT OF INTEREST GENERATED BY MY PREVIOUS POSTING ON
> THIS SUBJECT THAT I'VE BEEN ASKED TO POST IT GENERALLY TO THE REFLECTOR
> WHERE IT CAN BE VIEWED BY ALL AND ARCHIVED.
> SORRY TO THOSE WHO'LL RECEIVE TWO COPIES BUT ALL IS NOT LOST BECAUSE I'VE
> SINCE MADE A SIGNIFICANT REFINEMENT TO THE FIX - PLEASE SEE THE FINAL
> PARAGRAPH ADDED BELOW...
>>> Dear OMs,
>>> I promised to share the results of my recent request for advice on the
>>> subject of 160m RF v DSL modem incompatibility.
>>> Firstly, many thanks to the kind Ops who offered me their very
>>> valuable advice. This email is primarily addressed to you and those Ops
>>> who've requested info.
>>> Based on this advice I've now managed to find an acceptable solution in
>>> following way...
>>> Having firstly established that the RFI was not a result of direct RF
>>> radiation within the shack and/or into the power circuits, by making
>>> transmit tests into a screened dummy load. I then installed ferrite
>>> on both DSL modem leads but these gave no improvement.
>>> The telephone extension socket provided in the shack was at the end of a
>>> long run of internal telephone extension cabling which I suspected was
>>> acting as an rx aerial for the RFI. So I rearranged the cable
>>> interconnections around the house
>>> so that the incoming Telco NTTP (master socket) was directly cabled into
>>> shack by the shortest possible route from the external Telco
>>> distribution point (OH pole). With the
>>> remainder of the house 'phone cabling temporarly disconnected, there
>>> now complete absence of any RFI breakthrough into the DSL modem, even at
>>> max RF power levels !
>>> I've now arranged for the remainder of the internal 'phone network to be
>>> connected to the shack
>>> master socket via a standard 'phone plug. So, when operating on 160m,
>>> all of
>>> the house cabling can be isolated from the modem by temporarly pulling
>>> plug. This realises an acceptable solution given that my 160m operating
>>> normally only undertaken during very early mornings and late at night. A
>>> 'phone is permanently connected in the shack anyway via a DSL filter to
>>> cover any emergencies.
>>> I hope that my experience and solution will help other Ops suffering
>>> the same problem.
>>> I'm lucky in that my 160m TX antenna is located about 60 metres from the
>>> shack and Telco NTTP. For
>>> stubbon RFI cases, especially where the modem or cabling is being
>>> swamped by RF due to the
>>> TX antenna being in closer proximity, more drastic action could possibly
>>> involve; maximising the use of ferrite chokes on the modem leads, (being
>>> mindful of their possible attenuation of the DSL signal as well).
>>> Shielding the modem in an earthed metal/foil enclosure . Replacing
>>> some or all of the internal 'phone network with screened cabling.
>>> of the DSL modem cable entry points with 10nF capacitors.
>>> Unfortunately, I'm not aware of any available band stop/pass filters
>>> suitable for the modems.
>>>PS: Refinement - I've since inserted a large common mode ferrite choke
>>>between the modem socket and the cable feeding the rest of the internal
>>>telephone extension network. This was very successful, now making it
>>>unnecessary to make any disconnection to the house 'phone network whilst
>>>operating. (Choke was abt 5 metres of 'phone cable around a large ferrite
>>>core salvaged from a scrap TV/monitor's defln coil.)
> I realise everyone's operating environment & requirements are going to be
> different but hope that the principles found during my experience can be
> adapted to help other Ops find a cure when having similar problems.
> Good Luck and 73 Dave G4GED
>>> ----- Original Message -----
>>> From: "Dave_G4GED" <daves_shack at tiscali.co.uk>
>>> To: <topband at contesting.com>
>>> Sent: Monday, October 24, 2005 3:41 PM
>>> Subject: Topband: 160m & DSL incompatibility
>>>> I know many top-banders monitor the Internet DX Clusters etc whilst
>>>> operating on the band.
>>>> I wonder if anyone who's suffered from dropped DSL connections due to
>>>> RFI into the DSL modem has managed to find a fix?
>>>> My DSL line drops just running 100W on Topband. Other bands have no
>>>> I've tried wrapping the in/out leads thro' ferrite cores with no
>>>> I think the DSL runs at freqs very close to 1.8Mhz so maybe a sharp
>>>> or high pass filters are necessary?
>>>> Any thoughts? Please reply to my personal email address as this
>>>> may be considered off-topic.
>>>> If there's sufficient interest I'll post a resume of suggestions
>>>> Mni tnx 73 de Dave G4GED
>>>> g4ged at arrl.net
>>>> Topband mailing list
>>>> Topband at contesting.com
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