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
>> the
>> 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
>> chokes
>> 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
>> the
>> 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 was
>> 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
>> the
>> plug. This realises an acceptable solution given that my 160m operating
>> is
>> 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.
>> Decoupling
>> 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@tiscali.co.uk>
>> To: <topband@contesting.com>
>> Sent: Monday, October 24, 2005 3:41 PM
>> Subject: Topband: 160m & DSL incompatibility
>>
>>
>>> Hi
>>> 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
>>> 160m
>>> RFI into the DSL modem has managed to find a fix?
>>> My DSL line drops just running 100W on Topband. Other bands have no
>>> affect.
>>> I've tried wrapping the in/out leads thro' ferrite cores with no
>>> improvement.
>>> I think the DSL runs at freqs very close to 1.8Mhz so maybe a sharp
>>> notch
>>> or high pass filters are necessary?
>>>
>>> Any thoughts? Please reply to my personal email address as this subject
>>> may be considered off-topic.
>>> If there's sufficient interest I'll post a resume of suggestions
>>> received
>>> afterwards.
>>> Mni tnx 73 de Dave G4GED
>>> g4ged@arrl.net
>>> _______________________________________________
>>> Topband mailing list
>>> Topband@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/topband
>>>
>>
>
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