[RFI] DSL INTERFERENCE FROM 160 METERS

[Cortland Richmond]

Probably the nature of the beast. 

ADSL uses spectrum up to 1.1 MHz and ADSL2 up to 2.2 MHz.  At maximum reach
there is only about a few uV difference between bits in the digital signal
,and this makes it sensitive to noise of any kind.   An in-band RF signal
is *supposed* to result in deselecting blanked carriers, but it sounds to
me as if the modem front end is desensing when you run 160.

In tests on an early ADSL system yrars ago, I found immunity could be
improved if a receiving modem were isolated (the green wire wasn't
filtered) and hefty RF common-mode filteriung added to the power and
telephone lines. Radio Shack DSL filters might help, but you need a really
high impedance common mode (bifilar is best) choke to cut the 160 meter
signal down at the modem input.

Cortland
KA5S


> [Original Message]
> From: WA3GIN in Alex. City, VA <wa3gin at erols.com>
> To: WA3GIN in Alex. City, VA <wa3gin at erols.com>; Commander John
<crazytvjohn at yahoo.com>; <rfi at contesting.com>
> Date: 2/6/2007 8:42:39 PM
> Subject: Re: [RFI] DSL INTERFERENCE FROM  160 METERS
>
> I was talking about the phone line not the AC line feeding the filter,
> although that might help as well depending on the input source of the RFI.
> In my case the phone line drop was about 6 feet from the dipole element
so I
> know there was significant RF energy coupling into the phone line.
>
> 73,
> dave
> wa3gin
>
>
> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of WA3GIN in Alex. City, VA
> Sent: Tuesday, February 06, 2007 8:35 PM
> To: 'Commander John'; rfi at contesting.com
> Subject: Re: [RFI] DSL INTERFERENCE FROM 160 METERS
>
> I use a CORCOM EMI/RFI AC line filter in-front of the modem.  Put the
modem
> on the load side and ground the filter chassis. Any RF coming on the
twisted
> pair will be shunted to ground in the filter leaving the DSL modem to do
> what it does best.  The filter specs are adequate to allow the needed
audio
> pass band for the DSL to operate at full potential.  
>
> These filters can be found at Fair Radio surplus for less than $10 the
last
> time I looked.
>
> 73,
> dave
> wa3gin
>
>
> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of Commander John
> Sent: Tuesday, February 06, 2007 8:16 PM
> To: rfi at contesting.com
> Subject: [RFI] DSL INTERFERENCE FROM 160 METERS
>
> I just got on 160.   Operating at 1955kc my signal interferes with my at&t
> sbc DSL modem.  Its a two wire  No problems elsewhere.
>   50 watts will cause the modem to shut down fast.  
>    
>   How do I protect my modem from the RF.  I don't know much about DSL what
> frequency does it use?
>   john w9zy 
>
>
>              
>    
>    
>   W9ZY
>                 .... Commander John ....
>                          
>    
>
>
>
>
>
>
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