Speaker failure

Yesterday the Medion computer speakers that I used with my Elecraft K3, failed. I was WSPRing on 10m and had the speakers switched off at the time but I saw some unusual interference on the waterfall and switched them on to listen. Nothing happened. No audio, nor did the blue power LED light up.

I checked the obvious things such as the cables and that the power supply was delivering 14V DC. It was. I took the speaker containing the audio amp over to the workbench and tried it on the bench power supply. Although the speaker was behaving as if no power was being applied, 20mA was being consumed when the switch was on. I have no idea where it was going.

Without a schematic there isn't much I can do but I doubt that the speakers are repairable anyway. There are no active components on the circuit board apart from one integrated module attached to a small aluminium heatsink. This has presumably let its smoke out. There are a number of capacitors on the board and the cable connections are extremely well filtered against RFI. I have never seen such attention paid to preventing RFI. I guess that this is because Medion is a German company and Germany seems to be the only country that takes compliance with EMC standards seriously. The speakers were almost completely immune even when I ran 100W. Having a tone control they produced very rich-sounding audio from the K3, unlike its internal speaker which is shrill to listen to and has very little bass response.

I've now replaced the Medions with a pair of passive speakers that I originally got for this task but with those the audio sounds boxy no matter how I fiddle with the K3's RX EQ settings. The only benefit of them is that I'm using one less wall wart!

These Genius speakers look like they might be a good replacement but ordering a pair would be a lottery as I have no way of knowing if they are RF-proof enough. One pair of Logitech speakers I bought were a dead loss. They were handed to the local Oxfam shop within an hour of the postman delivering them as they were so sensitive to RF they were beyond hope.

Death of short wave imminent

Amateur radio as we know it could be extinct by the year 2020. That is the only possible conclusion to draw from an unpublished EU policy document that has been leaked to several ham radio bloggers including myself. The document proposes that existing RFI standards protecting the short wave frequencies be torn up as "preventing the use or increasing the cost of essential technology in order to protect the activities of a small number of hobbyists makes no political sense." This policy has already been unofficially in place at the UK's Ofcom, which was one of the major contributors to the report.

The report suggests that withdrawing the standards relating to short wave RFI would save significant costs by removing the need to deal with complaints about interference. It also suggests that the UK Telecommunications Act (and similar laws in other EU countries) be amended to remove any right to protection from interference of the broadcast, amateur or CB services.

To support its recommendations the report claims that "short wave broadcasting is in rapid decline, with most broadcasters moving to the internet" and that "the intended use of Citizens Band as a personal communications service has largely been replaced by cellphone usage." Amateur radio, it says, carries "little communication of any importance that could not be made using the telephone, cellular network or the internet." The main use of ham radio, it suggests, is "largely recreational" and could be replaced by "online simulations and VOIP chat services." Hams could also make more use of the largely interference-free bands above 400MHz which otherwise could be sold to commercial users. Radio amateurs "could still experiment with radio in the time-honoured manner, they just should not expect to be able to enjoy interference-free reception on the short waves."

The reason for the desire to remove the protection of our frequencies becomes clear when you read the part of the report that describes forthcoming technologies that are expected to cause problems with RFI compliance. In order to meet carbon emissions targets and deal with expected power shortages caused by the early closure of nuclear power plants in countries such as Germany, the EU plans to introduce smart grids in all European nations by 2020. These smart grids use BPL technology to communicate with smart meters in each individual home. The smart meters, in turn, use PLT technology to communicate with smart devices in order to regulate their use. When demand for electricity is high, power cuts or the switching on of expensive standby power stations can be avoided by shutting off inessential devices instead. Examples of inessential devices given in the report include amateur radio linear amplifiers - assuming it's still possible to hear anything on short wave over the BPL and PLT QRM in the first place.

The EU is also proposing that 80% of properties in member states should be equipped with solar panels by 2020. To achieve this target, installation costs will be heavily subsidized by governments, which clearly want to cut costs as far as possible. Estimates produced by a Chinese manufacturer of solar power systems suggest the cost saving that would result from eliminating the need for RFI suppression circuits in the power converters would amount to 4 billion Euro for the whole of Europe.

The report concludes that "the cost of protecting the short wave spectrum from interference from technologies that are essential to be installed throughout Europe in the next decade to meet emissions targets and maintain the well-being of all European citizens is quite simply prohibitive" and urges that EU Commissioners pass the necessary laws by 1st April 2012.

Well I'm filtered

Just over a month ago I purchased a pair of Medion Multimedia PC Speakers from Aldi and was delighted at both the quality of the sound they produced from my Elecraft K3 and the fact that they were free from any RFI. So when I observed some loud rasping noises in time with my voice while operating 80m SSB a few days ago I was a bit surprised. After a bit of experimentation I discovered that this was due to the fact that I had decided to power the speakers from my Diamond GSV3000 25A shack power supply in order to avoid an extra wall-wart. When I powered the speakers from the provided supply they were free of unwanted noises.

The ability to power the speakers from the same supply as the radio seemed worth pursuing, so I decided to investigate. Another nice aspect of these Medion speakers is that they are held together using easily accessible Phillips screws and can be taken apart in a couple of minutes. All of the other computer speakers I have had were put together in an unfathomable way so I could not even begin to attempt adding RFI suppression.

Once I had the thing apart I was very impressed with the trouble that had been taken to filter all the cables going in to the powered speaker. Both positive and negative lines of the power input are filtered using several turns of wire on opposite sides of a toroidal core. The stereo line input has capacitors across the input, and the output to the other speaker has wire links with a ferrite bead on each one.

Clearly the interference was coming in on the power cable, so I added a 10nF capacitor and a 470uF electrolytic capacitor across the output of the choke filter. To my surprise this did not make the slightest difference. I am puzzled by this, but life is too short to waste trying to find a solution when one already exists, so I am now running the Medion speakers using the unregulated 12V wall-wart the manufacturer provided.

New Hamsphere released

As someone who tried, out of curiosity, Kelly Lindman SM7NHC's VoIP ham radio simulation Hamsphere a couple of years ago, I received a notification that HamSphere 2.0 has just been released.

I haven't tried this new version and I'm still very aware of what happened last time someone blogged about something like this. Since no radio is involved, I find it hard to find any lasting interest in making "contacts" with it.

But in view of the gloom I presently feel over the UK government's attitude to the PLT interference issue, the fact that I received an email about this on the same day seems foreboding. I'm starting to wonder if amateur radio will soon be something like Sinclair ZX81 games or Space Invaders machines that we will only be able to experience via a simulation.

Another kiss-off for UK PLT fighters

It comes as no surprise to me to learn that the second attempt to use an online petition to force the UK government to outlaw home networking over power lines (PLT) devices has been given a diplomatic kiss-off, just like the first one. The government's response - which you can read in full here - concludes "On the available evidence, we do not believe an outright ban of all powerline equipment is justified."

The response was so predictable that I didn't even bother signing this petition. The online e-petition site exists simply to give the impression that democracy exists in this country and that ordinary people's views count. The results show what a lie that is.

The only things that count for anything in this country are money and votes. There are too few radio amateurs to influence anyone's electoral results. And as long as it is cheaper for British Telecom to solve reports of PLT interference by "replacing the apparatus, hard wiring and conventional wireless alternatives" than to withdraw the offending devices, that's what it will do.

There were 121 reported cases of PLT interference in the UK in the last year, and according to the government's response 104 were resolved in the abovementioned manner. What the reply doesn't say is what happened in the 17 cases that were not resolved. It would appear that 17 UK radio amateurs are no longer able to pursue their hobby because of this.

The response also states that "the Regulator’s investigations found no breach of the EMC requirements." If true, this suggests that the regulations aren't strict enough to protect the ability of radio amateurs and listeners to receive weak signals on the short wave bands.

We're all doomed! The steady increase in noise levels due to the proliferation of all kinds of electronic devices is something that most of us have experienced unless we are fortunate enough to live in the middle of nowhere with no neighbours. I seriously doubt that ham radio will still exist as a hobby in ten years' time.

Pet ferrites

Ferrites are my friends. You can never have enough clamp-on ferrite RFI filters. Unfortunately just about every radio and components stockist charges a ridiculously high price for them, like £2.50 (about $4) each, which makes it expensive to keep a stock of them. However, a few weeks ago I found an eBay seller in China that was selling packs of 6 or 10 clamp-on RFI ferrites at a much more acceptable price, so I sent off for a bunch of them.

This afternoon the K3 was sitting scanning 2m 144.250-144.350 while I was working, and I noticed a 3 S-point increase in the background noise level. My wife had just switched on her laptop, so I thought that might be the culprit, and sure enough we soon found that the noise was being radiated by the power supply cable. Even if the power supply was off and the computer was running from its battery, the noise level jumped up when the power cable was connected. One turn of the cable through a clamp-on ferrite was all it took to fix it. (Most PC power supplies seem to have a moulded-on ferrite at this point, but curiously not this one.)

A few weeks ago I used clamp-on ferrites to cure a problem with my Elecraft K3 transmitting a poor PSK31 signal (high IMD) on 10m. What seemed to be happening was that RF was getting picked up on the shield of my 2m antenna and coupled back to the K3, causing the problem. I dare say the real cause is a poor RF ground, but it's hard to get good grounding at 28MHz when you're about a quarter wave above ground already. Anyway, fitting clamp-on ferrites to the antenna cables and any other long cables that seemed to be contributing to the problem seem to have cured the trouble.

Clamp-on ferrites have also been quite effective at keeping RF out of the computer. The mouse would freeze when 100W is used on some bands, but looping the USB cable through a ferrite soon fixed it. Without having a box of ferrites sitting patiently in the cupboard, I might have wasted a lot of time trying to find another solution.

Noise cancelling

When I moved to this QTH in 2001 the electrical noise on the HF bands was quite low considering this is a high density residential area. But noise levels have risen over the years.

About two years ago I was disturbed to hear a constant "arcing" type noise at a strength 7 to 8 affecting most of the HF bands 15m and below. I first noticed it when switching on the radio after a few months of inactivity, so I did not know exactly when it started. A neighbour had taken delivery of a new TV during that period, and the interference seemed to be coming from his house. However, when I tried to raise the subject the neighbour denied having anything that could be causing interference, so I was unable to pursue it. I resigned myself to having to live with the interference.

A week or so I ago I observed that what sounded like the same interference had increased in strength to S9+10dB on 20 metres, making the band unusable. Again, I wasn't sure exactly when it happened as my interests had been diverted to the higher bands 10, 6 and 2 metres for a couple of weeks. It seems possible that changes I made to the antenna system at the time - such as adding 10m and 6m elements to my multi-band dipole - may have increased the pick-up of the noise. 40m and 80m were similarly afflicted.


I was unenthusiastic about trying to raise the matter with my neighbour again, since even if I was able to show that his TV was causing the interference, it seemed unlikely that he would agree to buy a new one just to keep me happy. Someone recommended trying an MFJ-1026 noise cancelling unit, and reviews on eHam.net suggested that these can be very effective at eliminating noise from a single point source, so I decided to order one. It was delivered on Friday and I spent much of the holiday weekend trying it out.

The principle of the noise canceller is that you have a second antenna which ideally should receive just the noise you want to eliminate. You then balance the signal strength of the two antennas so that the strength of the noise is equal, and adjust the phase of the two signals so that the noise received on the noise antenna cancels out the noise received on the main antenna.

The MFJ-1026 is sometimes advertised as an "active antenna with noise cancelling", and comes with an internal antenna and preamp. However, this is really pathetic at picking up anything on the lower frequencies. Although it did pick up enough noise that I could cancel it out on 20m, this could only be achieved by reducing the gain of the main antenna to a low level to match the noise level received by the whip. It was completely ineffective on 80m.

The manual advises erecting a second "sense" antenna. However, even a random length of wire proved to be a poor antenna on the lower frequencies, just as it would be for normal receive use. What's needed, if you are going to use a non-resonant antenna, is an ATU to get the maximum signal out of it.

It occurred to me that I could use my Wonder Wand L-Match antenna (similar to a Miracle Whip) as my noise antenna. This picked up a considerably stronger noise signal on 20m, allowing a higher main antenna gain level to be used. It also allowed the MFJ to cancel noise more effectively on 80m.

I have made an MP3 sound clip that demonstrates the difference that the MFJ-1026 noise cancelling unit makes on 20 metres. The first five seconds of the recording are with the noise canceller switched out so you can hear the interference at full strength. Then I switch the noise canceller in, the noise vanishes, and you can hear a conversation that you could barely tell was there, never mind copy, before. I switch the noise canceller out and in again a couple more times during the 30 second clip so you can hear the contrast. Click here to listen to the sound clip.

I should be overjoyed to have eliminated this awful interference from 20m, my favourite band. Actually, I am a bit depressed. It all seems like a messy kludge. I had to rearrange my desk and make up new cables to locate the MFJ-1026 to one side, because it was rather an eyesore sitting above the K3 right in front of me with the huge Wonder Wand telescopic practically touching the ceiling.

Changing bands is no longer just a button press. I have to tune the Wonder Wand and then adjust the MFJ's level and phase controls as the settings change from band to band, even from one end of the band to another. And the MFJ-1026 is no use with my little QRP rigs, which don't generate a strong enough signal to activate the RF-sensed TX changeover in the noise cancelling unit.

But when all is said and done, the MFJ-1026 does a pretty good job of removing this particular noise source. It's better than going QRT, which may well have been the only alternative.

Logitech S120 speakers NOT RFI proof!

I am presently using a pair of cheap Trust SoundForce 2.0 computer speakers bought from the local Wilkinson store with my K3. I originally bought them to use with the JUMA since Gerd, who built it, hadn't included an internal speaker. However I tried them with the K3 and found they were a substantial improvement over the built-in speaker. With several turns of the input cable wound on a clamp-on ferrite choke they are almost immune to RF breakthrough even at 100 watts. However, they look a bit cheap, I felt that the sound quality could be improved, and I would be happier with no RF breakthrough at all. Unfortunately I couldn't find a way to get inside the speakers to install extra suppression components. Although two Philips screws are visible at the base of each speaker, the case halves also appear to be secured by screws at the top which are behind the grille, and I can't see how to get that off.

I saw some Logitech S120 speakers advertised on eBay and decided to order them, as they looked a lot nicer, and matched the K3 better, and since they came from a "quality" brand I thought their RFI suppression might be better. The speakers arrived this morning, and are already back in their box to take to the local charity shop. The sound quality was better than the Trust speakers, but I was dubious about how they would perform in the presence of RF since even before I transmitted I could hear a faint pulsating buzz - possibly caused by a DECT telephone base station nearby.

The RFI was so bad I got a loud buzz even on a tuning signal of 6W on 15m. When I pressed the mic PTT with 100W selected the resulting burst of noise almost caused a need for a clean pair of underpants! I can see no way to get inside these speakers at all, but even if I could, it would probably be hard to make them RFI proof given that the susceptibility is so bad to start with.

My loss is the Oxfam shop's gain - and yours, as I decided to post this as a warning. Logitech S120 speakers should not be used within 100m of a radio transmitter - at a very minimum. I just hope that none of the neighbours is using them.