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Author Topic: Help with EMI  (Read 14654 times)
KD9AXI
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Posts: 14




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« on: May 06, 2014, 06:34:57 PM »

Guys, I am a new ham, just got my General in April and am using an ICom 738 with a G5RV Jr antenna and a Zepp 80 meter balanced antenna.  My problem is I have background static in the S7-8 range. I have operated the rig on battery and killed power to the house and still have interfernce.

I took an am radio out this weekend and was able to start at my house and trace the static to a food preperation plant about a block from the house( it also extends behind my house but that is open space) I talked with my neighbor who is employed by the local electric utility and he tells me taht while they don't have the equipment to track the noise they did work with the local cable company about a year ago on very similar problems and they traced the problem back to the same plant. 

The company has been approached by myself and other neighbors on various issues and the basically tell us to take a hike, they will do what they want.  This is a small town and they local adminstration basically lets them get away with it.

Where do I start?  The electric company manager doesn't want to put in writing about what they found with the cable company.  What steps do I take and is there anything I can do to at least get on the air? Right now I can't get through the static unless someone is running 1000 watts and then they can't hear me.

Thanks,
Don
KD9AXI
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KI6LZ
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« Reply #1 on: May 06, 2014, 07:29:28 PM »

You will have to file a documented complaint to the FCC.

1. Absolutely identify whether the noise is being generated through the power lines, cables or plant.

2. Document all noise with video and audio recordings with comments and date/time stamps.

3. Document and date all conversation.

The noise should end at plant closing unless they run 24/7/365. Verify this and record it.

It is important for the FCC to know who to sent a violation notice, so you must be sure of the offending party(s).
 
Tell the offending party(s) that you are in the process of filing a complaint to the FCC. Show them some recent violation notices the FCC has sent to recent violators. You can find them on line, think recent one had to do with electric fences or water pumps.

Good luck.
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W0BTU
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« Reply #2 on: May 06, 2014, 08:00:00 PM »

In the meantime, you might try building a small tunable receive loop. They have sharp and deep low-angle nulls broadside to the loop, and often work great to null out local noise. You transmit on your dipoles and listen on the loop.

I had one years ago. It was made from 1/2" hardline and was about 3' in diameter. Plans are likely in an ARRL Antenna Book. It was on a stand and could be manually rotated.

I used one of these preamps, mounted right at the loop: http://www.w0btu.com/W0BTU-broadband-preamps.html and fed it with surplus CATV coax. A simple bias tee circuit fed the 12 VDC right through the coax.
« Last Edit: May 06, 2014, 08:02:31 PM by W0BTU » Logged

WX7G
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« Reply #3 on: May 07, 2014, 04:54:00 AM »

S7-8 noise on 80-20 meters using an SSB filter and your antenna is the new normal for an urban environment.

To determine if the noise is from one dominant source or if it's from numerous sources this question needs to be answered:

Is this noise level continuous across an entire band or does it peak at specific intervals?
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WX7G
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« Reply #4 on: May 07, 2014, 06:09:36 AM »

http://ftp.rta.nato.int/public/PubFullText/RTO/TR/RTO-TR-IST-050/TR-IST-050-02.pdf

The median noise formula on page 2-15 of this report gives a noise level at 7 MHz of 28 dBuV/m in a 9 kHz bandwidth. Received on a 7 MHz dipole terminated into 50 ohms the noise voltage at the receiver is 41 dBuV in a 9 kHz bandwidth or or about 36 dBuV using an SSB filter. 36 dBuV is 63 uV which is 2 dB over S-9. So, we see that a noise level of S-7 to S-8 is to be expected in an urban environment. 
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KF7CG
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« Reply #5 on: May 07, 2014, 06:43:14 AM »

The big question in all this is how good are the S-meter readings? The S-meter on my FT-950 tends to read about 1-2 s-units high compared to the "standard". So the S-meter could stand calibration just to make comparisons more valid. At one time an article appeared on how to do this.

KF7CG
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WX7G
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« Reply #6 on: May 07, 2014, 08:16:01 AM »

The Elecraft XB-2 calibrator is designed for calibrating S-meters.

But in any event the urban noise floor has increased due to the proliferation of electronic devices and is expected continue to increase. The FCC has no plans to address this from the noise generation side. They are looking into addressing it for AM BC by possibly increasing transmitter power.
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KI6LZ
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« Reply #7 on: May 07, 2014, 08:24:22 PM »

I might believe S7-8 noise levels in an inner city, but not in normal single family block neighborhoods. On 40 meter my noise on a calibrated S meter runs about S4-5 during the winter months, S8-10db over 9 during the summer storm season.

This is atmospheric noise and not power line or other noise generators. When I switch to AM detection I hear no AC 120 Hz hum.

I do have the Elecraft calibrator and my 2 SDR receivers are dead on. Also measured linearity with precision attenuators.
« Last Edit: May 07, 2014, 08:26:27 PM by KI6LZ » Logged
W0BTU
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« Reply #8 on: May 08, 2014, 03:39:55 AM »

Regardless of what might be normal, that doesn't mean he should just throw up his hands and give up, or just accept it. We already know where at least some of his RFI is coming from. He should try and reduce it.

File the complaint, and while you're waiting for that (probably a long time) erect a low-noise receiving antenna of some type. There are many different kinds for small city lots, besides what I suggested.
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N3HEE
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Posts: 127




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« Reply #9 on: May 08, 2014, 10:18:04 AM »

You will have to file a documented complaint to the FCC.

1. Absolutely identify whether the noise is being generated through the power lines, cables or plant.

2. Document all noise with video and audio recordings with comments and date/time stamps.

3. Document and date all conversation.

The noise should end at plant closing unless they run 24/7/365. Verify this and record it.

It is important for the FCC to know who to sent a violation notice, so you must be sure of the offending party(s).
 
Tell the offending party(s) that you are in the process of filing a complaint to the FCC. Show them some recent violation notices the FCC has sent to recent violators. You can find them on line, think recent one had to do with electric fences or water pumps.

Good luck.

I agree with this plan but step 1 will require specialized equipment that can take and work with specific noise signatures.  It's like taking a fingerprint of the noise and then finding a match.  Even with this gear it's tricky to find the correct source of noise.  You may need to get an RFI specialist involved at some point if this goes to court. 

Your best bet is to convince the suspected noise source\s, power company, that you plan to aggressively pursue this matter and that it will start to cost them money once you do.  Once they figure out money is involved they will change their tune and start working with you on resolving the issue.

I'm surprised the power company doesn't have RFI equipment and personnel available?  Double check that by opening up a complaint ticket with the power company.

Be prepared to spend lots of time and some money resolving this issue.

Be patient, kind and helpful at all times.

In the meantime you can learn about low noise antennas from W0BTU !!



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NO2A
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« Reply #10 on: May 10, 2014, 09:20:48 AM »

Don,does the noise level suddenly drop when the company closes? All it takes is 1 computer left on to create hash. Have you ever operated later or late at night to verify this? With 80m it`s hard to say. Sometimes I get s7-8 noise on 80,while 40 might be s2-3,or even s0. Much of that is simply atmospheric noise. The receive loop is a great idea. I`d try a portable hf receiver for 80m,at least you could probably operate that way. The problem with 80m is it simply picks up everything nearby. I even hear cars driving by(ignition,fuel pumps,etc.)I found my laptop power supply generated about s3 noise on 40m,and was picked up by my 80m low dipole. Without it plugged in my noise on 40 was s0! Sometimes the noise goes down later at night for me,on 80m. Especially real late,like 12 am.
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W0BTU
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« Reply #11 on: May 10, 2014, 11:15:45 AM »

Don,does the noise level suddenly drop when the company closes? All it takes is 1 computer left on to create hash. Have you ever operated later or late at night to verify this?

What's the noise level during the day. Or maybe I should ask, what time of day do you hear this noise level?

I looked at a satellite photo, and it looks like his house is too far from the factory to pick up that much noise from a computer. My guess is it's noisy variable-speed motor drives (perhaps using IGBTs) that need filtering.
« Last Edit: May 10, 2014, 11:37:01 AM by W0BTU » Logged

W0BTU
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« Reply #12 on: May 10, 2014, 11:34:21 AM »

In the meantime you can learn about low noise antennas from W0BTU !!

Well, I appreciate your vote of confidence; but the only low-noise RX antenna that I know much about is the full-size Beverage antenna. The OP doesn't have room (probably) for a Beverage, but I have some alternative RX antennas for limited-space listed at http://www.w0btu.com/Beverage_antennas.html#If_theres_no_room_for_a_Beverage .
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KD9AXI
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« Reply #13 on: May 11, 2014, 12:10:36 PM »

The noise is 24x7, they are running extremely large compressors and flash freezing units even when shutdown,  my suspicions invole the large  sodium or other halide lighting they use may also be involved.  They power company involved is small, approximately 3000 customers so i believe them when they say they don't have the equipment needed to track it down so don't want to cause them too much hassle if they can't do it.  I can show them noise  at the top and bottom of the sine wave of my incoming power so they believe me.  This customer apparently has caused them numerous problems
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W0BTU
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« Reply #14 on: May 11, 2014, 12:29:59 PM »

The noise is 24x7, ...  I can show them noise  at the top and bottom of the sine wave of my incoming power

Holy smokes! This noise is being sent out their incoming power lines?!

The FCC needs to be contacted, as others have pointed out. And maybe a little media publicity. If you approached your nearest TV news people the right way, perhaps they would tell the whole community. That might help motivate them to fix this.
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