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EMI and other Power Related Noise




 
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Author Topic: EMI and other Power Related Noise  (Read 1118 times)
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Steve - K4HX
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« on: June 02, 2019, 02:05:06 PM »

From WA7JHZ:

The attached JPG shows the 80-75 meter noise floor both during and after a local power outage on Sunday 26 May 2019. The FCC needs to be more aggressive when it comes to shielding and filtering of manufactured electronic equipment. This noise floor level really compromises the reception of 75 meter AM signals at my residence.

For example: several years ago, I bought a used Pentium computer for $20. I reformatted its hard drive and installed Windows XP. It worked great, but it wiped out AM reception at my home. I removed the power supply and found that it was missing its common-mode choke and capacitors. In place of the common-mode choke were two copper wire jumpers. I added the choke and capacitors, and the noise was gone.

A Chinese manufacturer saved a few Cents by omitting the choke!

If more Hams were aware of increasing urban electronic noise sources, perhaps they might petition the FCC for tougher RFI regulations through the ARRL. This will only get worse.

David S. Forsman, WA7JHZ


* Avista Power Off and On 5-26-2019.JPG (275.93 KB, 2000x700 - viewed 146 times.)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #1 on: June 02, 2019, 02:48:57 PM »

I completely agree David. I found that almost ALL Chinese manufacturers of switching supplies for LED drivers and GP have there materials tested, got the CE and/or other approvals and than start producing without filters. They don't seem to feel any barrier in fooling people and the bad EMI situation. There is NO way to purchase LED lighting in Costa Rica with the filters mounted. Most equipment though DO have place for it at the PCB and do have their approval, but no filters mounted. When I switch the LED lighting on, no FM reception, a few TV channels gone and no shortwave/medium wave reception. The situation is that bad that you can't even use a lightning detector due to the mains noise in and around the house. This situation is purely due to the complete lack of control of the government and the Chinese attitude. I could not find any  LED materials from other origin than China.
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KK4YY
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« Reply #2 on: June 02, 2019, 10:13:36 PM »

Twenty dollar computers aren't what they used to be.
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W3MMR
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« Reply #3 on: June 03, 2019, 12:40:03 PM »

My noise floor at my QTH on the ANAN 200D is never below -75dbm, or 2db below s9 on 80m. Sometimes it's as bad as 10 to 15db over s9. I live in the City, 7 miles SW of Center City Philadelphia. For a comparison, my father who lives 35 miles SE of me in New Jersey out in the country, his noise floor on his ANAN 7000DLE is never higher than an s3, generally its an s2. In the evenings, guys are generally 20 to 30 over 9 so its bearable, but it gets really annoying when guys around me can here a certain person and I cant. Its the same on other bands too. s7 on 40m, s5-s6 on 20m, s6 or s7 on 10m. Drives me nuts... And heres a link to a video of the noise on 80m and the AM Broadcast Band, which is almost wiped out... Dont pay attention to the s meter in the video, i had messed up the calibration at the time.

https://youtu.be/EIWGFQs5TNQ

Oh and by the way Don, i heard you talking to steve and the guys this morning. Sounded great.

Perry
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KK4YY
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« Reply #4 on: June 03, 2019, 04:48:17 PM »

Perry,

Thanks. Glad I was able to get above your noise floor. Grin


Don
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W3MMR
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« Reply #5 on: June 03, 2019, 09:06:30 PM »

Haha, well unfortunately it was on Steve's WebSDR. I cant copy anyone but Nick, KG2IR, and sometimes Bruce, WL7B, during the day. Oh and John W2WDX. Generally anyone past Long Island, fugetttaboutit. Nevertheless, ya sound great. You have a voice made for radio lol
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** Studio "A" - Anan 200D, Shure SM7B, AL80BX, Internal & External Processing <--> Studio "B" - Heath-Kit DX100, D-10/4, National NC-303 **
wa1mtz
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« Reply #6 on: June 17, 2019, 12:53:32 PM »

another noise source are the mini-split a/c units I just put in a 18,000 btu Mitsubishi, had to put emi filter on the input line and another one feeding the inside unit- got the best corcom units from quest electronics. They will qrm segments of the b'cast band and hash from 1720 to 5,000 kc, the manual states the a tv set (at uhf) can be qrm'd if the antenna is close to 10' from the unit. The compressor operates at a variable frequency up to 150 cps. "inverter technology" The fujitsu units I've been driving past can qrm the car radio up to half mile.
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kb2vxa
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« Reply #7 on: July 23, 2019, 11:41:34 AM »

It's pretty obvious your noise floor or lack thereof depends on the proximity of neighbors, they all have electronic feldercarb of one sort or another. Don't expect any help from the FCC even if pressured by the ARRL and every ham in America, like everything else it's all about money these days. If you have an EMI/RFI problem your only recourse is to find Hernando's Hideaway, no HOA Nazis, and plenty of room to move... good luck.
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73 de Warren KB2VXA
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Patrick J. / KD5OEI
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« Reply #8 on: July 23, 2019, 10:30:55 PM »

How is the noise floor properly measured?
Is it done at end of the cable normally connected to the receiver input?
Is it done with an antenna matcher is in place and tuned to the frequency in question?
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KK4YY
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« Reply #9 on: July 24, 2019, 04:12:26 PM »

How is the noise floor properly measured?
Is it done at end of the cable normally connected to the receiver input?
Is it done with an antenna matcher is in place and tuned to the frequency in question?
In absolute terms? No idea. Maybe a good time to hookup an isotropic antenna  Grin

In relative terms, as it relates to local area RFI, turn your battery powered receiver on during a power blackout and measure the noise floor against the reading you get when power returns.


Don
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N4LTA
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« Reply #10 on: July 25, 2019, 01:54:22 PM »

My experience is that you don't have to get far from the house to greatly reduce the noise. I bought an active antenna designed and built by a guy in Virginia - I think he got sick and sold the rights to DX Engineering. I applied all of his recommended chokes and ferrites and place the antenna at the edge of a pond about 250 feet from my house and further than than from other houses in the neighborhood. I was amazed at the drop in noise level and the increase in S/N level.

I was using it to receive 60 Khz to 500 Khz with my experimental license. I have not used it in several years and tried it a few weeks ago. It appears to have had a surge and is not working. I have a spare unit and may try to get it back in operation. This past week I was testing my old dipole for 75 meters with a K1JJ tuner  have built and the noise level is so high on that antenna it is almost worthless on 75 meters. I haven't been active for 3-4 years and am shocked at the noise increase on the dipole - which I am sure is due to computers, modems, wireless modems and TVs.

Going back to the active antenna may be the only way that I can operate again.
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KD6VXI
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Making AM GREAT Again!


« Reply #11 on: July 25, 2019, 08:05:23 PM »

Pretty hard to fight common mode noise I gress with open wire line.

Choking a coasshole fed dipole with ferrite at the feed point and at the place where it comes into the shack can work wonders to limit noise incoming.

I've heard of 3 to 5 plus s unit decrease in noise levels on rx by doing this.

I don't know how you would make a common mode choke with owl.

My owl dipole in the city of Bakersfield was nearly useless because of neigh ors solar and tvs.

Now that I'm back in the country (20 acres on a retired apple orchard), I can't wait to try owl again.

--Shane
KD6VXI
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