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Author Topic: Cause for concearn?  (Read 5135 times)
KE4JOY
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Posts: 1335




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« on: October 22, 2012, 02:09:48 PM »

Last night while operating on 15 meters phone I got a phone call from the wife telling me that I was "bleeding  through" on the amplified computer speakers. It was quite intelligable.

Now we have not noticed this before but she may have not had those speakers on while I was on the air before so we dont know if this is new.

Anyhow I did a little research and concluded that amplified computer speakers are highly supceptable to RFI espically at HF. This relieves me some. But I am a little concearned about getting into the neighbors gear.

Is there any cheap and easy way to check for harmonic emissions?
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WB2WIK
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« Reply #1 on: October 22, 2012, 02:15:09 PM »

Sure there is, but harmonic emissions have nothing to do with this. Wink

What's interfering is your primary radiation, intended signal.  A harmonic, if your transmitter was absolutely terrible, would be 30 dB down from that, or 1/1000th the power of the intended signal.

If your neighbors haven't complained, they're probably not having any problems.  It's a "proximity" thing.

Amplified computer speakers are notorious for this.  All the ones I had years ago are happily occupying a landfill in Newhall about now.

Some really good, very "high end" computer speakers (not high volume, just very high quality) might be better than the standard ones most people use.  You can sometimes reduce or eliminate the problem by wrapping the signal and power line cords multiple turns through large ferrite cores, and bypassing the input signal (computer to amplifier) with a .01uF disk bypass capacitor right inside the speaker/amplifier unit.
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KE4JOY
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« Reply #2 on: October 22, 2012, 02:41:56 PM »

Yes, good point about the harmonics, glad I dont have to chase that down. I had read the 'fixes' you mentioned in my brief research on amplified computer speakers. Thanks for the tips.

Well I guess for now I just wont be able to operate while she is watching netflix!
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WX7G
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« Reply #3 on: October 22, 2012, 05:17:59 PM »

She might try switching OFF the speakers and using headphones.

Or, I guess for now she just wont be able to watch netflix while you operate.
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K1CJS
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« Reply #4 on: October 23, 2012, 04:19:58 AM »

Quite a lot of the time, those speakers are powered by a wall wart, and that is where the signal gets into them.  If those speakers are powered by a clean power supply, your signal wouldn't be causing that problem.  If you can, get rid of the wall wart and power those speakers from a better supply. 

Sadly, most of those speakers run off 9 volts, and there is no way to supply power to them unless a fairly expensive supply is purchased.  That's why the best answer may be to get better computer speakers.
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K4JPN
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« Reply #5 on: October 23, 2012, 10:01:41 AM »

I found that winding several turns of the power cord and audio line through a ferrite filter works great.  A cheap source of ferrite to use as a filter is the flyback transformers in old TVs, just wind the cord around the ferrite  8 or 10 turns. I have use them to eliminate RFI in my answering machine and computer speakers.   Otherwise buy the clip on type of ferrite filters and make several loops thorugh the filter, make sure you get the clip on filters for the frequency you are having problems ie. 3 to 30 MHz.
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KD0REQ
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« Reply #6 on: October 24, 2012, 11:04:43 AM »

the blue cores in old computer power supplies are IF range, 100-800 KHz, they should swamp anything above audio with a few turns.  I've had good luck with those for a while, and the price is right.  otherwise, open up the speaker cases at the weld line and put .01s across the input, speaker, and power leads.
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KE4JOY
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« Reply #7 on: October 25, 2012, 12:59:04 PM »

I am not really all that concerned about the RFI in my equipment. As has been said she just cant watch netflix while I am operationg or has to get headphones  Wink

The dipole does run right over the house but is up at least 40 feet from the roof line. I just hope I am not getting into the neighbors stuff.

One thing I have not checked is to see if the room with the computer is on the same branch circuit as the shack. Wouldent supprise me.
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KE4JOY
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« Reply #8 on: October 25, 2012, 02:20:59 PM »

Well evidently you cant modify posts here so sorry for the bump.

It turns out that the shack and the computer share the same branch circuit so maybe some common mode stuff going on there?

So yea I am not so worried now.

Thanks!  Grin
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WB4BYQ
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« Reply #9 on: October 26, 2012, 05:57:36 AM »

If they are still for sale,  buy her a pair of rfi proof West Mountain RFI proof computer speakers.
They are still for sale,  look at West Mountain Radio under the audio section.

Richard
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K8AC
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« Reply #10 on: October 27, 2012, 04:38:01 PM »

Two thoughts:  I agree that harmonics have nothing to do with this situation.  But, just as a learning experience, you might want to figure the harmonic frequencies for the bands you typically operate and then see what other services might be using those frequencies.  That exercise will show you that it's not a harmonic problem. 

Second, someone mentioned the West Mountain RFI proof speakers.  I previously had a set of cheap amplified PC speakers for which  I never could eliminate the RFI when operating at 1500W out on 160M.  The cabinets were all glued together and there were no connectors involved and the leads were too short for chokes.  So, saw the West Mountain speakers on sale and tried a pair of those.  I've had no problems getting into those while running full legal power on all bands from 160M to 10M.  You ought to be able to achieve the same with just about any PC speakers with the right chokes, etc., but if you see the West Mountain speakers at a good price, it may be the best way to go.

73, Floyd - K8AC
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WN2C
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« Reply #11 on: October 28, 2012, 11:07:54 AM »

You could be coming thru the computer and not the speakers if the netflix feed is over internet via computer, fed to the TV w/ an HDMI cable. I had a neighbor tell me that I was coming into their phone and then his wife tells me well it's not the phone but the computer has a recording device that records all phone calls. They could hear me when they played back a call. That was what I was getting into. He was running flat wire for the phone hook up and his Son switched to cat 5 twisted pair and that has apparently solved his problem. I say apparently cause I haven't heard anymore about it.  Sounds like common mode and some well placed chokes should take care of it.

73 de wn2c  Rick
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