LW/MW/SW local noise sources

[G6Tanuki]

We're all fighting a battle against sources of RFI/burbles/sharsh that raise the noise-floor or otherwise wipe-out our ability to listen to our traditional signal-sources.

Here's a heads-up: the battery-recharger shown below is a potent source of S9+++ RF noise across MW and SW frequencies. Even when the batteries are charged it continues to extrain a comb of RF nasties.

I do hope you return it for a refund! Not just turn it off when listening.

[G6Tanuki]

It's sadly not mine to condemn.

[Cobaltblue]

Others here may know better than me but as I understand it there is virtually no requirement on radiated interference below 30MHz.

There are requirements on conducted interference.

Above 30MHz the picture is quite different.

Cheers

Mike T

[Andrew2]

Trouble is, garbage 'conducted' onto the mains wiring is radiated by the wiring far and wide. My mate has bought himself an LED porch light (finest Chinese quality) from E-bay and the noise it whacks onto the mains interferes up to 70-odd MHz. He has dissected it and there is no sign of any suppression/filtering components whatsoever. Sadly, Joe Public buys the cheapest and we will soon be surrounded by this rubbish.

[vinrads]

I had the same problem it turned out to be caused by the new Gu10 LED lamp's recently fitted in the kitchen ,so much for saving power. Mick.

[turretslug]

Originally Posted by Cobaltblue

Above 30MHz the picture is quite different.

Yep, it's where the money is- short-range, high data-rate transmissions. I fear that there is simply no motivation for the powers-that-be to keep sub-30MHz clean, it's regarded by those with clout as a minority interest, obsolescent usage piece of spectrum of little use or consequence with the resultant ever-increasing interference making this a self-fulfilling and exponentiating prophecy.

[jsbhavsar]

India is notorious for RF noise on radios due to inside and local equipment. We all use flourescent tube lights here. Many residents still use copper choke with starter. I migrated to the electronic chokes of Philips which are better. But then locally made cheap electronic chokes are available that add quite a lot of noise on my national ekco A731 tube radio.
Other equipment in India which always remains closeby due to smaller homes and dense housing:
- Laptop chargers if they dont have "CE" mark
- Mobile phone chargers
- ADSL modem routers
- WiFi routers
- Digital Set Top Box of the TV
- Refriegerator

etc

[mikeald]

I have a switch mode psu in the kitchen, feeding the led strip lights. THis causes interference through 3 solid brick walls right the way to the end of my garden...

[vu2nan-nandu]

In my shack the desktop PC is the biggest culprit!

Regards,

Nandu.

[Hybrid tellies]

In our house it's my old 17 year old crt tv which is now driving the tube hard and radiates hash across much of the MF and HF bands and is gradually getting worse. All the switch mode power supples for the laptops and switch mode chargers for the mobile phones, mp3's etc. But by far the the worst offender is my Philips Freeview STB which wipes out everything from 150Khz to the FM band. Even on the strong local AM stations it causes a nasty background noise right around the house. Luckily I can switch the damned thing off at the power socket when it's not in use.

[Radio Wrangler]

The permitted interference levels for CE mark approval were derived from a few assumptions which explain what is happening

1) Their object was to protect us from our neighbour's equipment, not from our own and this is enshrined in the permitted levels and test distances.

2) It was assumed that there was only one problem device in action at any one time (Ho-ho)

3) Bands and signal levels of 1980s broadcast service areas were most protected

4) Max levels in test receiver bandwidths of 9kHz and 120kHz were specified.

the last of the above is subtle. You can't allow anything to put out interference above a certain level, but you can put out almost an unlimited number of unwanted signals provided they are spread out and the number which can be seen at once in the test receiver bandwidth is below the permitted level.

So manufacturers exploited this and took steps to scramble interferers to spread them wider than the test receivers so the measured level fell, even though the total output rose.

So now we have high hash levels, aided and abetted by the rise in the number of devices, aided by nergy efficiency regulations forcing SMPS where something simpler would otherwise have been used.

Add to this the amount of non-compliant stuff where EMC filter components are no longer fitted and linked out.

David

[AC/HL]

As regards being forced to use SMPS, I suspect simple market economics would have led us here. The falling costs of Electronic circuitry coupled with the rising costs of transformers will lead to the inevitable with or without external pressure.

[G6Tanuki]

Originally Posted by AC/HL

As regards being forced to use SMPS, I suspect simple market economics would have led us here. The falling costs of Electronic circuitry coupled with the rising costs of transformers will lead to the inevitable with or without external pressure.

Yes - apart from the energy-efficiency considerations which predicate against old-style "iron and copper" PSUs, one of the big benefits to a manufacturer is that a SMPS will work on anything from 90 to 260V, AC or DC, and if AC without worrying about frequency.

Design and approve one SMPS design, ship it to all markets. And no worries about complaints/warranty-claims from customers when they travel abroad and plug a 110V-only PSU or device into 230V mains.

Even the simple weight-reduction of a SMPS over an old iron-and-copper transformer can make a significant saving if you're regularly air-freighting a few million iPhones from China to the USA.


In practice I find the biggest cause of "hash" in my locality is from CFL and LED light-bulbs. I've recently taken back to Screwfix for a refund a batch of 240V LED GU10 bulbs because they generated horrendous broadcast-band interference. Shame, as they gave a really good intense kitchen-friendly "cool white" light with nice beam-dispersion: however I'd rather prefer they confined their emissions solely to the visual spectrum!

[Keith]

If you want the full chamber of horrors try this site:

http://www.ukqrm.org.uk/

[McMurdo]

This universal laptop adapter broadcasts a fast motorboating sound on AM throughout the entire house on any radio not tuned into strong station. I spent a fruitless half hour trying to align a wireless a couple of weeks ago due to the adapter swamping my loose-coupled RF signal generator. Thinking the set was showing bad RF instability, I swapped valves and replaced various decoupling caps until I decided to try another radio..that one had the same noise.

Sold under a few different brand names, I bought it not because it was cheap but because it had the best selection of 'ends' and it was one of the few powerful enough to power my dated laptop at 120W.
It came from a high-street shop, though they no longer have it listed. It's still available under different brandings. It's CE marked.

[Andrew2]

I have two laptops in my shack - one for running the spectrum analyser and one for the SDR's. Both the mains power units are surprisingly quiet, just a gentle 'whizzing' sound if I put a radio close.
Most of the noise in our house seems to come along the mains, possibly from next door. A loud buzzing sound is audible in the background behind GOLD on 1458 KHz, which is a massive signal, and the bottom end of MW is infested with hums, whines and general hash. I've given up trying to use any kind of random wire aerial for receive on the MF/HF bands and instead use a wideband loop.

[AD360 Rob]

I have a similar issue from next door too, I can tell when they turn on their TV by the AM band becoming all but unusable except on the strongest stations. I have exactly the same model of Samsung TV yet mine doesn't produce any appreciable noise at all, same with my computer, sky box, laptop, NAS drive, However, my nice new LED security light radiates RF like a 4kw white noise generator.
Progress indeed !

[Phil G4SPZ]

Perhaps I'm lucky. My shack/workshop is at the bottom of our small garden, not far from the nearest neighbour's house but I don't seem to get too much trouble from external sources. This might be because the timber building has twin walls, in between which is 2" thick aluminium foil-faced insulation which, although not earthed or bonded, may act in part as an electromagnetic screen.

That said, on long wave my two fluorescent lights emit a sharp 50Hz buzzing and have to be turned off for listening. On MW the circular fluorescent lamp in the illuminated magnifier emits a continuous squawk of unstable frequency. With a short external wire antenna I don't notice any particularly bad interference on short waves.

The worst I ever encountered was a horrid rasping interrupted sawtooth noise caused by a pair of mains-signalling data networking devices in my own house. Like McMurdo, I initially thought I had a fault on the radio under test, as the noise wasn't present on LW or MW but swamped a wide section of the SW bands.

My personal opinion is that CE-marking and the EMC regulations are a joke, and are being flouted with impunity by unscrupulous manufacturers and importers, who face scant risk of prosecution, whilst burdening genuine manufacturers with high compliance costs. Enforcement is by over-burdened Trading Standards departments which are, quite rightly, having to prioritise the removal of poisonous alcohol and other illicit substances from the streets.

[dansteele]

ever so slightly off topic (FM) but, the vintage style Edison squirrel cage filament lamps that are currently popular with interior designers, if not dimmed, will produce interference around 100MHz, enough to prevent listening if I recall!

(this took me a long time to track down and never suspected the lamp in the corner of the room was to blame)

Dan