[RFI] Resolving RFI to a DSL Modem

Cortland Richmond ka5s at earthlink.net
Sat Mar 21 12:37:50 EDT 2015

Some years ago, I worked for a telecommunication manufacturer (DSC Communications, later Alcatel USA) who made digital loop carrier equipment. One of our projects was a carrier-less AM ADSL line card, which would allow every subscriber line card to also provide ADSL service. 

Unfortunately, it was failing to work in trials, a problem I was able to localize not in our line cards, but in separately sourced receiver modems the telco had selected; it was exquisitely sensitive to any RF noise, even a momentary spike due to static, brush noise or a solenoid deactivating. I tracked this down to a "low bidder(?)" wall wart that lacked RF filtering and a receiver's CM choke that didn't have enough.

At long distances from the line card, there is very little difference between amplitude of adjacent bits in the data constellation, less than two microvolts, and this can lose sync quite easily.  You might get a really good common mode filter for the power, and see it that helps.


-----Original Message-----
>From: Kim Elmore <cw_de_n5op at sbcglobal.net>
>Sent: Mar 21, 2015 11:32 AM
>To: rfi at contesting.com
>Subject: [RFI] Resolving RFI to a DSL Modem
>I have an  ADSL modem in my garage and when I operate with anything more 
>than 1300-1400 W on 40 m only, it loses the ADSL connection. I';; be 
>getting an IPDSL modem on Monday, though not Uverse (because... Well, 
>it's the phone company). I'm assuming I'll have a similar problem with 
>it, if not worse. I've ordered five of the ~1.5" ID type 31 ferrite 
>cores, enough for one per wire that enters or exits the device. How many 

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