The AM Forum

THE AM BULLETIN BOARD => Technical Forum => Topic started by: Steve - K4HX on June 02, 2019, 02:05:06 PM

Title: EMI and other Power Related Noise
Post by: Steve - K4HX 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

Title: Re: EMI and other Power Related Noise
Post by: PA0NVD 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.

Title: Re: EMI and other Power Related Noise
Post by: KK4YY on June 02, 2019, 10:13:36 PM
Twenty dollar computers aren't what they used to be.

Title: Re: EMI and other Power Related Noise
Post by: W3MMR 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.

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


Title: Re: EMI and other Power Related Noise
Post by: KK4YY on June 03, 2019, 04:48:17 PM

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


Title: Re: EMI and other Power Related Noise
Post by: W3MMR 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

Title: Re: EMI and other Power Related Noise
Post by: wa1mtz 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.
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands