[RFI] Disconnecting from Internet?

dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Tue Apr 29 12:42:54 EDT 2003


I interpret your situation as most likely being caused by RF overload into
the modem.  You don't specify, but I get the impression that the modem is
internal to your computer.  The fact that you can drop your power to 60
watts, or less, and apparently operate without problem is indicative of an
overload situation.

The telephone cable is probably not the only cable into/out of the computer
"main box".  You most likely have a mouse cable and a keyboard cable, plus
the monitor cable (assuming the computer is a standard desk top unit and
not a notebook type) and perhaps a pair of speakers.  One or more of those
cables may already be fitted with a ferrite "chunk", but those ferrites
tend to be dedicated to helping the computer manufacturer meet CE (and FCC)
emission limits from 30 MHz on up.  So, a ferrite designed to add impedance
in the HF region is needed to help reduce the effects of coupled RF on all
of those cables (antennas) below 30 MHz.

The first suggestion would be, of course, to get further separation between
the antenna and the computer.  Since that appears to not be a convenient
solution in your case, the next idea would be to improve the overall
shielding of the computer main box if applying ferrites to all external
cables does not cure the problem.  That can be a nasty business unto
itself, so let us hope that more cable decoupling will do the job.

Suggestions have been made in previous postings by other writers about
making use of an RF sniffer probe or current meter in detecting where you
have the "hottest" cables.  Such a device might prove useful to you in
refining the hunt for the primary RF coupling means into the modem.  Best
wishes for success.

73, Dale

                      "Richard, M5RIC"                                                                                                 
                      <m5ric at talk21.com        To:       <rfi at contesting.com>                                                          
                      >                        cc:                                                                                     
                      Sent by:                 Subject:  [RFI] Disconnecting from Internet?                                            
                      rfi-bounces at conte                                                                                                
                      04/29/2003 09:52                                                                                                 


When using more than about 60W on HF I get disconnected from the Internet.
Its only on some bands but its still very annoying.

I have tried ferrite rings round the telephone cable near the computer but
it hasn't helped. I have a very small garden so am unable to get the
antenna further away from the house. I have a simple wire doublet that runs
from the chimney above the room down to the end of the garden, in the
centre there is ladder line down to a SGC-230 tuner mounted on the wall.
There is a small choke balun before the coax from the tuner goes back to
the shack and I also have a choke balun in the shack.

Any suggestions on what to do??

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