[VHFcontesting] CATV RFI from 2m SSB

WBR/WF4R wbr at verizon.net
Wed Feb 16 14:29:57 EST 2005


>Figured I'd send this post out to the VHF reflector since it has nothing to
>do with HF operations...
>I was working a *very* open 2m band on SSB last night and afterwards got a
>phone call from my neighbor asking if I had "been on that ham radio?"  
>I reluctantly admitted so, and he said I was killing his television and
>coming through on his computer speakers (computer wasn't even turned on).
>He lives two houses down and unfortunately my beam is pointed right at him.
>Luckiliy(?), his TV is on cable (CATV) and I think this EMI problem can most
>likely be solved.
>I've been reading through the material on the ARRL website.  They suggest
>trying a common mode choke first for CATV interference.
>I'd like to get some suggestions from you guys on the following:
>1.) Is this most likely a common mode EMI problem?
>2.) Should I consider putting a filter on the output of my amplifier?  I am
>running a Mirage 3016 on 2m (160W out).  Yes, I've verified that I *do* need
>the power to work the stations I talk to regularly.  I'm sure since this is
>a solid state amp that there are spurious emissions of substance.  Anyone
>have a recommendation as to what filter I should use?
>3.) If I want to try a common mode filter on his TV coax, what ferrite
>should I use?  ARRL says use #43 ferrite for low VHF, but this is 144MHz.
>4.) I told my neighbor that I'd not transmit until I was able to come up
>with some possible solutions.  If you have any good ideas, please let me
>know.  Again, I'm in the midst of reading all the material on ARRL.org, but
>if there are some experienced guys out there who have some good advice,
>please let me hear from you.
>VHFcontesting mailing list
>VHFcontesting at contesting.com
           Just as an obtw,  cable channel 18 happens to be right in the 
2 meter range.  CATV  cable leakage  could be a problem.   A lot of TV 
sets simply do not have adiquate shielding.   My old TV was that way.  
But when I bought a newer TV, it evidently had much better shielding,  
No more TVI.
      Are the computer speakers powered types?  It may be that even 
though the computer is not powered up, there is still power on the 
motherboard and thus maybe the sound card.  (?)  In an ATX power supply 
the motherboard is always partially powered.  Soome motherboards even 
have an LED to indicate so.  
    I've found that no matter how many ferrite beads you use, the best 
way sometimes is to just wrap every lead in aluminum foil.   It doesn't 
look very pretty, but it's effective.
      Sometimes you can get lucky and just wind a couple of turns in the 
leads themselves to make a choke.  I've had very good success with this 
    Another obtw,  cable channel 24 is right in the middle of the 222 
MHz band.  Sometimes you just can't win.  Good luck on attenuating it 
73, Bill, WF4R

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