Finding receiver noise issues

Here’s a timely reminder, not to assume anything when it comes to radio.

I recently bought an ICOM IC-7300. With its SDR receiver it performs very well, better than any other receiver I have used. Not only is it sensitive, it’s noise blanking and noise reduction features are very good and add to that its twin pass band filters and the manual notch capability and if there’s a signal there, I can usually hear it.

What happened about 6 weeks ago however, is my base noise level on 40m went up from S4/S6 to S9/S9+10db. I initially thought the noise was from a local farmer connecting up his (faulty) electrical fence again but after “coping” with this noise for several weeks, hoping the farmer might move his animals and with them the fence, I realised that the noise was not the same pulsing noise that I had last year and rather a white broadband constant noise. Having just changed Internet connectivity, I wondered if that could be part of the problem. Then I decided rather than guessing what it might be, I’d plan a way to track down the noise.

Step 1. Check whether it’s noise coming from your own house.
As Computer systems are known noise generators, I turned off both my computer and that of the wife (both of which are on almost constantly during the day) and nothing changed with regards to the high noise level.

To to do further investigation I’d be dropping mains power so I had to be able to run the IC-7300 on battery power. A new battery connector (Molex) plug was ordered and a new power lead made up. I then ordered a LIPO battery to power the rig (this would be used later for portable and demonstration operation of the IC-7300 - but I’m not taking this rig up a summit - at least not one, where there is any amount of climbing or even walking to do, as its too heavy).

Now I had to wait for an opportunity when the main power switch to the house could be turned off. When this came I first took a sample reading on 7.150MHz in normal operation - the S meter on the IC-7300 was constant on S9. I then switched to battery power - no change (so the PSU I’m running the IC-7300 from is not the problem).

I switched off the main house power and came back o the rig and the noise level indicated on the S-meter had dropped to S6 - Aha! the problem is somewhere in the house! (or at least the S6-S9 portion of the noise was being generated in the house).

I put the power back on to make sure the interference came back and not that the interference had coincidentally stopped - It hadn’t - the 40m noise level was back up at a constant S9 on the meter on the IC-7300.

Step 2. - Track down where the noise is coming from in the house.
The first place to check is the room where the rig is located, so a day later, I once again powered the IC-7300 off the LIPO battery, checked the noise level - again S9 and then simply unplugged all units including power boards from the four wall sockets in the room.
Guess what - the noise level went down to S6 again! So the problem is actually in my “shack” room. From there on it was a matter of plugging the items back into each of the wall sockets until the noise returned. Of course it came up again as I plugged in one of the power boards. In this case I had two power boards “daisy chained” to power various computer related items. I was able to exclude items on the first board by unplugging the cable to the second board from it.

So the noise producer was plugged into the second board. I reconnected the second board at which point the noise level increased up to S9 again and then proceeded to unplug each plug until the noise went down again. The culprit? A switched mode power supply, supplying power to a USB hub. I had suspected a “wall-wart” but we use so many these days it could be any one and the only way to find it was by the process of elimination.

Needles to say this wall wart is now in the rubbish bin and as it happens the powered USB2 hub is now plugged into the USB3 socket on my laptop and is drawing its power from there, so I don’t need to replace the switched mode PSU.

If you follow this guidance and turning off your main house power does not reduce the noise level, you know it is something either outside or in a neighbours house. That is obviously more difficult to find, but perhaps you’ll be lucky like me and find you were sitting right next to the source and you can remove it easily.

Now how to get that S6 outside noise level down somewhat …

73 Ed.


Typically, most HF noise sources will be “something with a cable”, it’s normally too hard to get an HF signal launched if there’s no antenna, i.e. piece of cable. This means that either the noise will be on the cable attached to the thing or injected into the house mains wiring.

In the case of your wall-wart, there are 2 things that you could try. The first is to install the cost-engineered suppression components that have been omitted. Most junk we get from China will have been designed with the suppression components in mind and a few items are made with them fitted for testing, evaluation purposes by the customer. Once the deal is signed, these are simple not fitted. Space can normally be found on the PCBs where the capacitors and chokes should be. The second is to detach the cable at RF. You normally do this by winding the cable onto some ferrite. This is enough to choke the RF and so without an antenna it doesn’t radiate. In your case, you would wind the low voltage cable on a torroid for a few turns. But the efficiency drops quickly below 10MHz so you may need a few toroids.

These two actions are normally enough to tame most noise sources. Whilst you have solved your problem by removing a PSU that was not essential, one day you’ll find something that cannot be removed or easily replaced. Practicing fixing these noise sources is essential for that day arrives. In my own shack I had a cheap PC case + PSU for a homebuilt shack PC that was enormously noisy. It turned out there were zero mains filter components in the PSU. Normally the IEC mains socket on the back is filtered but in this cheap machine it wasn’t. I swapped the filter for one removed from a dead PSU. Likewise all the USB cables produced noise and a few toroids at the PC connector end of the cables cured that and also stopped the PC rebooting should I run 100W RTTY on 17m,

I have a PSU for an external 2TB drive that is used for backups that destroys the bands from 20m up, it’s S9 on 23cms on the handheld even. But as that only gets turned on when the disk is connected and a backup is occurring then it’s not a big issue.

To ease location of the noise source, you want to make up a pair of E-field and H-field probes to go with your FT817 type of radio. These probes can be used to more accurately track the location of the noise (i,e. the PSU wall wart or its cables). Google is your friend for designs.


I know you mean well, Andy, but fixing electronics that have had suppression components fraudulently omitted is actually quite counter productive. What is really needed is effective protection by the law. We need a clear law with an effective bite to it that criminalises the import and retail of units with suppression components omitted. Make it the responsibility of the importer and/or the retailer to have effective quality assurance testing with large fines for failure, make it mandatory for consumer protection people to have equipment to detect non compliance or access to testing houses that can provide an appropriate service, and we can quickly improve the situation, which is frankly becoming desperate in urban areas.


Hi Andy - the cable transmitting the interferenence was most likely the power cable from the wall wart to the USB hub and possibly the USB cables plugged into the hub as well. As I said, the wall wart issue has been addressed - it has gone into the waste bin and no replacment is needed as the hub is now powering istelf from a USB 3.0 port on my laptop. In the majority of cases a USB hub does not need to be powered (indeed most don’t have the option). As this one had the option I used it.

I know about the removal of suppression components to save a cent or two once certification is achieved. When this is found to be the case, I’d like to see all of the offending company’s products needing to be retested and certifed at their cost, only in that way can this habit be stopped.

Several of my cables in the shack have been wound through Ferrite rings. This I did while trying to find how RF was getting into my speech compressor when using it with the IC-7300 when the problem didn’t exist with the Kenwood TS-2000. In the mean time, I have simply removed the external RF speech compressor, but the ferrites are still there. By the way the clip-on ferrites are totally useless at HF frequencies, you have to use proper ferrite cores.

Longer term, I think a better answer is a linear 5V and 12V shack supply with an output board so that items requiring either 5v (USB) or 12V can be supplied from one (known good and clean) power source rather than the lottery that is the supplied wall warts that come with everything today.

Interesting that you mentioned your external backup drive I have a Network Attached Storage (NAS) unit that was on my prime-suspect list - in fact it and it’s power supply are completely clean! In general I find that the PSUs that have a mains cable plugged into them - i.e. stiill switched mode, but not wall warts, are fine as they tend to be built to a higher quality level as they usually power more expensive equipment such as laptops and NAS units. Of course there will be some out there which are horrible but I think in far less numbers than with the wall warts.

I’ll look up E-Field and H-Field probes, thanks for the suggestion - I had been considering a magnetic loop or even ferrite rod antenna for use with the FT-817 and my RF noise hunt.

73 Ed.

Hi Brian,
See my comment above - I think it needs to be the producing company that gets hit with the costs of re-testing and by immediate removal of their certification of ALL of their products, the law already states that displaying a certification that you don’t (or no longer) have is considered an offence.

Realistically we’re not going to be able to enforce any fines on the Chinese companies or the importers but the inconvenience and additional cost of recertication on those companies could work as a deterant from removing components to save a cent or two.


For those looking out of a Torquay hotel bedroom and not expecting to see Sydney Opera House perhaps, The Hanging Gardens of Babylon, or herds of wildebeest sweeping majestically across the plain but have their feet firmly planted on terra firma then learning how to fix the issues yourself is the only way you will find to RF harmony.

Expecting your elected representatives or their appointed guardians of the spectrum to get off their corporate embigened fat backsides and do something about this is NOT going to happen. Why? Because $$$BIG-MONEY$$$.

Oh, it would be lovely if these people enforced CE marks and the like but $$$BIG-MONEY$$$ means it wont happen. So the only person who will fix these issues is you.

It’s all very well to say that, but these are the daytime noise figures for my set-up under battery power with the house power turned off:

80m S8
60m S8
40m S7
20m S7
18m S7
15m S5
12m S2
10m S2

All this noise may be originating in electronics that have noise suppression components omitted, but they are not in my house and I have no access to them. How about hunting them down? Fine in theory, BUT: on my street houses are every ten metres or so. I can put a whip on my FT817 and walk up and down the pavement and the noise barely alters from one end of the road to the other. One has to conclude that it is either coming from every house, or from the cables ducted just below my feet. Now it would be nice to live in a utopian world where all the sources of RFI are electronics under my control, but I live in a real world polluted by RFI from a myriad sources that are not accessible to me. Frankly, I have more chance of looking out of my shack window and seeing herds of wildebeest majestically depositing dung in my garden than I have of fixing these issues. Since you are so sure that £££BIG-MONEY£££ (£ - I live in the UK!) will prevent any action, I can only conclude that amateur radio is doomed because hams are prepared to bow under pressure and potter about fixing the noise sources under their control and living with the rest, instead of kicking up hell about the situation.

50-odd years a ham and I have to watch ham radio go out with a whimper. Vale!


Yes it makes me angry too…

The amount of EMC testing that a product goes through in this country compared to the rest of the world is laughable…

Though I guess the US is pretty tough too.


Brian, you will note in my original text, I said one should always look to ones own house FIRST. In my situation, being so close to at least one form of the interference and not spotting it sooner is somewhat embarrassing! How I track down the other noise, and what I do when I have found the source remains to be seen.

This problem is probably worse in (Geographical) Europe than Australia, however one of the justifications for the latest application to get 1KW on the HF amateur bands in Australia is that many stations suffer from the noise from uncontrolled RFI emitters and since the ACMA (equivalent of OFCOM) cannot resolve that problem, then the Amateur radio station needs more power to get over it. A totally wrong reasoning in my opinion, more action is required from the Radio Spectrum controlling authorities in ALL countries to clamp down and crush equipment that is unlawfully emitting RFI.

A single Radio Amateur going to the appropriate authority and complaining about a single case of a faulty wall wart in a neighbours home is likely not going to get much support. The authority needs to want to correct the problem, which they possibly shy away from as more of the public will see the intervention and possible removal of their latest electronic equipment (or parts thereof) negatively.

Now as soon as some company produces a wall wart that interferes with Joe Public’s TV or cell phone, THEN something might get done.


Ed, I completely agree that we should take steps - be proactive in the current idiom - to make sure that our own houses are clean of RFI. What I disagree with is repairing equipment that has noise suppression components omitted. Indeed, I am against even investigating the cause. If I get one it will go straight to the shop it came from and I will be banging on the counter of the returns department. If I get no joy out of them then it goes straight to the consumer protection people. This is what we should all be doing. I believe that there are over 70,000 hams in the UK, if they all start returning this sort of rubbish with loud and bitter complaints then at least the problem might appear on the edge of the radar!



110% agree Brian - crazy to try and repair the faulty gear. It didn’t make sense for me to return the wall wart, given that I bought it in Australia!


This is an interesting video

Use of E and H probes :

Below it are many links for probes and extra info

With the forthcoming demise of halogen lamps looming on the horizon in Europe (thanks guys) we will be faced with an insurmountable problem from the LED replacements. My house (and our previous shop) is all LED and I have little elevation of the noise floor but when the hotel next to my previous qth installed LED GU10 lamps I had S9+ noise from 1.8MHz to 5GHz
Testing with the owner I found that just one lamp would make amateur radio unusable from 0700 to 0100 every day. Replacing the bulbs with ones sourced from my supplier solved the problem.- in fact just one of those bulbs would make a useful noise source for other purposes (see, I can be positive!! :grin:)

Unfortunately, Joe Public will replace their GU10 with the cheapest replacement they can find and it takes only one bulb in amongst the thousands in an urban environment to cause absolute misery.

Gloom & doom - maybe, likely to happen - I would stake my pension on it.
Action by Ofcom - probably nil.:sob:

That’s the problem - you had it running upside down :wink:

Actually, believe it or not, I can still buy the old “real filament” bulbs here in Germany, but considering they’re “not allowed” to be sold in Germany, they are getting harder to find. The cheapo shops seem to have no respect for the “Greenies” - Good on "em!!

Also within 4-5 years MIT have announced they expect that the new high output, low power bulbs they have in early development will be available in commercial quantities. These bulbs (Globes to our US & Australian friends) are between 5 and 6 times MORE efficient than LED bulbs and give out the harmless white light, not the damaging white light that LEDs produce.

These will come in a glass gas filled packaging, fit into either a bayonet or screw type socket and use a filament that requires either 110v or 220/240v single phase AC electricity. What MIT have developed is a substance that the filament is coated with making it many many times more efficient than the current filament bulbs.

So for those planning to convert their lighting to LEDs, get ready to have to convert to this new technology within 10 years as it uses a lot less power than LEDs do !!!


Sounds like the Thorium on directly heated cathodes!
(Hope it lasts longer)

No MIT are using “Photonic Crystals”.

Try a pulsing S9+20 to S9+30 noise across the lower HF bands and only S8-9 on 10m which is what I get intermittently. I think the cause may be a faulty ethernet over powerlines (in house broadband over powerline), ina nearby house. Getting confusing test results, so not able to confirm it yet, but further testing continues.



What do you mean by “damaging white light” versus “harmless white light”? Does the bad stuff fade your Rembrandts or give you sunburn?


That has me puzzled, too - I always thought that white is white!