MW band pollution - Page 1
Forum section: electronics / rf-microwave

author: RoGeorge
author_rank: Super Contributor
timestamp: April 11, 2023, 07:48:48 am
content: Powered yesterday an AM radio, and all its MW band (531-1602 kHz) is full of constant noises and hummings and beatings. It's not a defective radio, a second one receives about the same. Only two national stations can be received, the rest is loud noises.I've un-powered and unplugged everything. The noise is about the same everywhere in the house. It comes from outside. It's on all channels (digital radio, jumps only on the exact frequency of each channel), and it's much louder than the sound from the 2 national AM stations. Tested in a city (Bucharest population about 2million).Romania still has a few national AM radio stations. I didn't listen to AM radio since the 90's, and remember reading along these decades how some countries officially discontinued their AM broadcast station. However, I don't think the norms against spurious RF have changed.Is this 'vrrrrr' noise normal nowadays?

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 11, 2023, 09:07:08 am
content: MW has been dead for years here, no more national stations, just SMPS and powerline modems. I guess since it's no longer in use there's not much regulation going on, nobody complains because nobody uses it anymore, welcome to the 21stcentury

author: RoGeorge
author_rank: Super Contributor
timestamp: April 11, 2023, 09:35:04 am
content: Yesterday evening (it was dark outside) I've thought it might be from all the SMPS driven lights around. This morning (full daylight) the noise was about the same.There are a few amateur bands in these PDF tables (valid 2020)https://ec.europa.eu/growth/tools-databases/tris/index.cfm/en/search/?trisaction=search.detail&year=2019&num=621&fLang=EN&dNum=2I Don't have any receiver for <10 MHz, all my SDR toys can receive only frequencies bigger than 50-100MHz.Is the noise present in the ham bands, too, for example in 3.5 or 7MHz?

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 11, 2023, 10:28:13 am
content: Quote from: RoGeorge on April 11, 2023, 09:35:04 amThere is some, but nothing compared to lower frequencies. I think the main source are things switching at a low frequency (10-100KHz), it gradually drops off going higher and at 1MHz it's significantly quieter already. I suspect that solar inverters are part of the problem, however mine just 'hisses' when getting very close. I quickly tried to find a source using my trusty Sony ICF 7600 but it looks like it's coming from all directions so most likely using the power lines as an antenna. Maybe I should fire up one of my SDR receivers and make a nice plot.

author: 807
author_rank: Frequent Contributor
timestamp: April 11, 2023, 10:36:16 am
content: Quote from: RoGeorge on April 11, 2023, 07:48:48 amIt seems that over the last few decades, manufacturers of switched mode type of equipment have been allowed to pollute the airwaves without any comebacks.When I was younger I could listen on long, medium & short waves without interference. Noways, unless you live in an isolated location, thats impossible.Do you or your neighbours have solar panels installed? They can cause RF pollution too.In the UK we still have a fair amount of AM stations, although they are gradually diminishing.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 11, 2023, 10:56:54 am
content: This is how the AM band looks here, plot from 0 to 1.8MHz. All the wiggly lines are the vrrrr noises.

author: Bud
author_rank: Super Contributor
timestamp: April 11, 2023, 12:08:12 pm
content: Quote from: RoGeorge on April 11, 2023, 09:35:04 amHams use SSB and CW modulation which are narrow band modes, so noise is much less pronounced.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 11, 2023, 01:21:10 pm
content: Quote from: 807 on April 11, 2023, 10:36:16 amI didn't see any, it's an area with 4 levels building blocks. The closest solar panels I know are on the roof of a supermarket, about 1km/0.5miles away.

author: ferdieCX
author_rank: Regular Contributor
timestamp: April 11, 2023, 02:39:49 pm
content: Here we have plenty of AM stations.There was some noise that bothered me when I tuned to a station that sends at 560 KHz, the culprit was a ZTE router provided by the telecom company.Using a Yaesu FRG-7 comm receiver, I could determine that the router polluted the whole MW & SW bands, emitting noise in multiples of about 300 KHz.This year the telecom company replaced the router with a new model, that is a little less noisier.

author: radiolistener
author_rank: Super Contributor
timestamp: April 11, 2023, 04:26:55 pm
content: That noise is produced by cheap Chinese electronics, they don't install filters to make it more cheap, so it flood environment with a high RF noise up to 4-5 MHz. Probably someone of your neighbors bought some cheap chinese device and when it is powered you're got that noise hell.But that noise floods mostly building, if you get your receiver and move 50-100 meters away from building and mains lines, you can listen a lot of MW stations with a nice quality.That noise affects not only MW, but also SW, FM broadcast and VHF bands. When mains outage happens for entire city, it's easy to listen FM and VHF stations from neighbor cities which is about 100-150 km away, because noise floor drops down very significantly and you can listen very weak stations as a clean signal.If you want to listen MW band, there is needs for external antenna placed as far as possible away from any buildings and mains lines. Also coax cable for such antenna needs to use ferrite RF chokes to block common mode RF noise which is received on outer side of the coax cable shield.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 11, 2023, 05:41:51 pm
content: Conect an external outdoor antenna and you will probably get better reception.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: April 12, 2023, 05:33:18 pm
content: Quote from: geggi1 on April 11, 2023, 05:41:51 pmAgreed. A source of intense local RF noise in the LW/MW band is domestic CFL lighting. Hardly EMC friendly, if not leaking RF direct into the air, these  luminaires are using the ring main as a loop aerial. I noted proximity RF noise from LED bulbs too - in particular the dimmable type. Add into the mix a household of computers, routers, ethernet over mains repeaters, televisions, television remote controls, cordless telephones, QI wireless chargers, and all of the other device crap that modern society cannot do without, then it's a wonder that DC to 1GHz is still transparent. btw My SDR does a very nice spectra of the RF noise produced by the computer that is required to produce the spectra of the RF noise received by the SDR.

author: boB
author_rank: Frequent Contributor
timestamp: April 12, 2023, 06:01:17 pm
content: My shortwave, HF ham radio and AM radio has been useless in my neighborhood for many years now.When the power goes off in the neighborhood, it all goes away and everything it useful.I had one time in the last couple of years to try the radios when all of the power went out due to a fire down the street.Then, when the power came back on again (and the noise), I turned off my house power and the noise was still there.So not my place. I had to move to another house in order to do HF ham radio again but even that, although better, is not perfect. Some EMI exists.boB

author: radiolistener
author_rank: Super Contributor
timestamp: April 13, 2023, 02:22:35 am
content: boBIf noise from your neighbors light is so strong, you can talk with them and propose deal to install filters for their noisy devices for your cost. Just explain that these noise interfere with listening to the radio, may be they accept such deal.Also it is possible that this noise emission exceed limits and FCC regulations, in that case they needs to power off such device and repair such device or install proper filter for their own cost.I know cases when ham amateurs proposed to install filters on mains for their neighbor, they accept that deal and it reduce RF noise.

author: boB
author_rank: Frequent Contributor
timestamp: April 14, 2023, 12:02:49 am
content: Thanks Radiolistener but my noise is from all over the neighborhood and not just one neighbor.I have a mobile station that I can move around in. Some neighborhoods are worse than others.This stuff is very hard to pin down. It might be emanating from the HV single phase power lines but I have not used my RTA to localize.When I walk around with the RTA, there is no place in particular where it is coming from.It is just dirty power from everyone I am pretty sure. Wideband noise and buzz with no particular frequency. That is why I think it is all mixed together.That's OK. I won't be living in that neighborhood much longer anyway.But thank you for the suggestions.boB

author: Kleinstein
author_rank: Super Contributor
timestamp: April 14, 2023, 09:52:25 am
content: There are a lot of SMPs around. So even of they are all within legal limits, it still adds up. In addition the the SMPS there are also inverters from PV installations with possibly relatively high power levels and "reasonable" antenna (PV panels). It is kind of a pitty, but there is not much hope for the MW band, except in remote areas. Anyway a main use for AM radio is to get at least some radio reception in more remote / mountainous locations where FM radio is not reaching. So it can still do this job.

author: A.Z.
author_rank: Super Contributor
timestamp: April 15, 2023, 03:23:12 pm
content: Quote from: geggi1 on April 11, 2023, 05:41:51 pmand to be sure to kill off that noise, try this antennahttp://www.kk5jy.net/LoG/

author: jonovid
author_rank: Super Contributor
timestamp: April 15, 2023, 11:54:26 pm
content: try this one-loop wire antenna 28 Meters long with a 24 to990400 pF variable capacitor on a 1x1 meter wooden square with a second 4 Meter long wire loop on the same 1x1 meter wooden squarefreeinga feeding 300 ohm TV type cable to your receiver,

author: A.Z.
author_rank: Super Contributor
timestamp: April 16, 2023, 08:34:16 am
content: Quote from: A.Z. on April 15, 2023, 03:23:12 pmjust to add some infoshttp://radio-timetraveller.blogspot.com/2022/05/the-loop-on-ground-antenna-for-noise.html?m=1HTH