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.

PLT a threat to British intelligence gathering?

A report produced for the British intelligence gathering organization GCHQ claims that noise from power line networking devices is causing a detectable increase in interference at its monitoring stations and could adversely affect its operations. The report, which can be found on the website Ban PLT, was originally released by GCHQ's Director of Engineering and Technology but has since been disowned by GCHQ which now claims it contained "inaccuracies." The government organization also forced the online tech news journal The Register, which published an article containing details of the report, to remove the author's identity from the article using measures designed, ironically, to suppress information that could be considered a threat to national security. So much for freedom of speech.

Ofcom meanwhile continues to deny that PLT devices cause a problem, stating that there have been "only" 272 complaints of interference (all from radio amateurs) and that of 233 cases referred to BT all but one have been resolved so there is nothing to worry about. Has pressure been brought from on high to force GCHQ to disown the report which is embarrassing to BT which has a couple of million of the Comtrend PLT devices installed nationwide? It is blatantly obvious that Ofcom couldn't give a damn about the possible effects on a few hobbyists who don't even pay a license for the spectrum they use. But a threat to the country's ability to monitor the short waves to gather intelligence about potential security threats is something they would have had to take seriously.

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.

Useful RFI

I apologize for being even more grumpy than normal but I haven't had much sleep. Olga and I were woken up at around 1 in the morning by a lot of noise outside. It was a group of young people who had apparently been having a party in the house opposite. Despite the fact that the temperature was heading for -7C and the girls, according to Olga who was looking out of the window, were none too warmly clad, they were not simply saying goodbye but continuing an animated conversation. Someone decided the party must be carrying on outside so they switched on a car's headlamps and turned on the stereo very loud. Because of the way the houses are crammed together here with virtually no front gardens this was taking place right below our bedroom window. After ten minutes we were both getting very angry. It isn't often that Olga uses the f word about people.

I felt like calling the police, but the chances of them actually making an appearance before the miscreants had slept off their hangovers was pretty remote so we discarded that idea. Olga went downstairs and turned on the lights to try and make it obvious that we had been disturbed. I went into the shack, switched on the K2 and sent a 10W dit on 30m, which switched on the security lights of the nearby neighbours that have them. This did appear to have the effect of making the tiny minds think "gosh, other people live around here and oh my, it's after 1 in the morning, perhaps they are trying to sleep and our noise has disturbed them!" because shortly afterwards the group dispersed and peace and quiet resumed. But neither of us are good sleepers and it took a while before we calmed down enough to sleep again. Hence the foul mood this morning.

It has sometimes been a bit annoying that I can't go on any band except 80m after dark because of the problem with security lights. But on this occasion it turned out to be useful. If only I knew that the thoughtless young people had touch sensitive lamps by their bedside I might even have been tempted to try a bit of all-night WSPR!

A DAB of interference

I think it is important when operating a ham radio station from home to ensure that none of your own domestic equipment suffers from interference. It's a sign that everything is OK, and if a neighbour should complain then it helps to prove the point that it is not your fault if you can demonstrate that your own TV, phone, stereo etc. are not affected by your transmissions. I've been surprised at the amount of power I've been able to run using antennas in the attic without experiencing any problems.

Last night I decided to use the digital DAB band of my radio tuner to listen to the Promenade Concert on BBC Radio 3 because Olga complained of hearing some high pitched noise (inaudible to me) on the analogue FM band, when played through a stereo amplifier and a pair of large 40 year old IMF monitor speakers. For a few minutes it was fine, then there were a couple of interruptions to the broadcast which I guessed were caused by the transmission of my APRS beacons. I think that the DAB transmissions are quite close in frequency to 2m so I shut down the 2m APRS gateway and we enjoyed the rest of the concert without interruptions. I imagine that the neighbours, if they listen to radio at all, will use analogue FM just as we normally do, but it is a bit of a concern that just 10W of 2m FM can cause interference to anything.

The only other known problem caused by my radio transmissions is a neighbour's security lights. I imagine this is a common problem. I installed an identical looking PIR controlled security light at the front of the house a few years ago after a couple of drunk youths wandered up our cul de sac one night and decided to uproot some of the plants in a neighbour's garden. I found that I could turn the lights on with as little as 5W on 20m. The solution was to leave our lamp turned off and hope that the neighbour thought it was the wind blowing the bushes around that was triggering his ones. Fortunately it is often windy here and I didn't used to go on the air in the evening all that often.

But my APRS gateway runs from morning to night and runs 50W output on 30m so the problem will become more evident as the nights draw in unless I adopt the simplest solution which is to shut it down (or switch to receive only) at nightfall. Breaking cover by admitting to a neighbour that I have been causing this to happen risks opening a can of worms that could put me off the air entirely, and remedying the problem would be expensive as his lights are part of a professional security installation that I would not be allowed to tamper with even if I wanted to.

Inspirational

My new work laptop came this morning. It's a Dell Inspiron 1764 with an Intel i3-350M(2.26GHz) Mobile CPU, 3GB of RAM and a 250GB SATA hard drive. It isn't the most portable laptop, having - like the Toshiba it replaces - a full-sized keyboard and a 17.3in. widescreen display. It looks and feels absolutely gorgeous, the screen is superb, the keyboard perfect for my fat fingers, and it's blisteringly fast. Click on the Firefox icon and the browser is there in a second or two.

What's more, the Dell doesn't cause any RF interference that I've noticed. The old Toshiba caused an increased level of hash that broke the squelch on my 2m FM receiver unless I cranked the knob round quite a way. Since I started receiving HF APRS I noticed that the Tosh caused a 3 S-point noise level on 30m as well, which all but prevented reception of any packets. So I am delighted with the new PC for that reason as well. I can now leave my radio station running all day as a VHF and HF APRS gateway while I work.

The old Toshiba had Linux installed on it early on in its life for security reasons plus the fact that Linux has some good web development tools. I was going to buy a PC with Linux preinstalled but I couldn't find what I wanted so I resigned myself to paying the Microsoft Tax. The Dell came with 64-bit Windows 7. I thought that I should try it under Windows for a few days just in case there was a fault and I had to send it back. But to be honest I think I may stick with Windows. It looks more polished than Linux, it's fast and I've already started to find replacements for the Linux tools I used. Firefox, which I spend most of the day using, looks and works exactly the same on both platforms, of course.

I certainly wouldn't choose Windows 7 64-bit for a shack PC as there are too many compatibility problems with popular hardware and ham radio applications. But for what I need to do to keep the business running it looks like being a good choice.

BBC to investigate interference complaints

Ofcom, the UK telecommunications regulatory authority, has announced that it will pass the responsibility for investigating reports of interference to TV and radio services to the BBC from July 1st. On that date, members of the public experiencing interference to radio or TV should lodge a complaint with the BBC using a web form, which may advise them of issues such as a local transmitter fault.

Some UK amateurs have expressed concern about the possible effect of this change, but I don't consider it likely to make much difference. As far as I can see, Ofcom will still be responsible for issues of interference to amateur radio such as that caused by PLT devices. These days, TVI and BCI are fairly infrequently experienced and almost always caused by a poor or faulty antenna installation or receiving equipment. Putting the BBC in charge of investigating complaints of interference to its own services makes a lot of sense.

Noises off

Show me a tidy shack and I'll show you the shack of someone who doesn't spend much time tinkering with equipment, or someone who has been nagged by his XYL to make the shack tidy and curses every time he needs to connect or disconnect something - which at G4ILO seems to be several times a week.

When I switched on the computer this morning there appeared to be a Sporadic-E opening building on 2m to the south east so I switched on the IC-910H and turned the SuperMoxon in that direction. Nothing was heard, so I switched to the vertical instead and was puzzled as to why the band noise was so much greater on the beam than the Slim Jim.

The opening passed, as all such openings have this year with nothing heard or worked, and I decided to investigate. I switched the computer off and the noise fell to the same level as on the vertical. Eventually, after much trial and error and cursing because the cables can only be reached by groping blind (with the aid of a shaving mirror or a picture of the back of the rig) behind the equipment I established that the problem was the serial cable providing PTT control to the interface connecting the 910H to the computer. Even when it was disconnected from the radio, plugging it in to the serial port on the computer caused the noise level to jump up.

This was a cheap interface I'd bought some time ago for the FT-817. The serial cable supplied wasn't screened, but I'd shortened it to use with a USB to serial adapter without a lot of spare cable lying around. This had resulted in it being too short to use with a real serial port, so I had replaced the cable. I had used screened cable for the replacement, but although I had connected the copper shield to the GND pin of the RS-232 port, it wasn't connected to the body or shell of the plug, which in any case was plastic.

I managed to solder to the metal flange of the plug, the bit that pushes on to the socket on the PC, and connect a short wire from that to the GND pin and the shield. That seemed to do the trick, and the noise level is now the same when the beam is pointing towards the shack as it is on the vertical. Problem solved, for once! Nevertheless I do sometimes wonder if computers are worth all the trouble they cause to us radio enthusiasts.

PLT DX Contest

For someone as plagued with HF band interference as me this sounds like a sick joke or an April 1 spoof that passed it's read-by date. The Electromagnetic Compatibility Industry Association (bet you didn't even know there was one) has announced a contest to see who can detect interference furthest from a power line adapter installation. Yes, really. There are two prizes: the Long Distance Award (LDX) for the person who detects interference the greatest distance from the installation, and the Most Typical prize (MTY) for the entrant whose detection distance is closest to the median value.

Well I suppose when interference blots out HF entirely we need to use our radios for something. I believe a CQ WW Wi-Fi contest in the offing. You collect SSIDs for multipliers. Double points if the network is unencrypted.

Bad ground

If you read any of the text books on setting up an amateur radio station they always tell you that you should connect everything to a good RF ground. What none of them tell you is how you get a good RF ground if your shack isn't located on the ground floor of the building. I have always tried to use co-ax fed antennas that are properly matched so that there is no RF on the shield of the cable to cause any problems. But in a nod to the text books I have always grounded everything to the copper pipes of the central heating system, which is the nearest thing to ground available in the G4ILO shack.

Today I noticed that 15m was open and there was quite a bit of activity on PSK31. I put out a call and was alarmed to find that my PSK IMD Meter was showing an IMD of around -22dB. Jan, UT5CO replied to my call, so I completed the contact and then investigated. The problem was only bad on 15m, and only when using the magnetic loop antenna.

First I tried my usual solution, which is to put clamp-on suppression ferrites on any cables that might be causing RF to get into the K3. I thought that solved the problem, but I was mistaken. I tried various other things without success and had reached the point where I thought I would have to avoid using the magnetic loop on 15m. (To my surprise, I found that my multiband dipole, which doesn't have a 15m element but is linear loaded on 40, can be matched by the K3 on 15m and works just as well as the loop, so that wouldn't have been too big a hardship.)

On a whim, I disconnected the ground wire from the K3 and the IMD immediately went down. Not all the way to -34dB which I got using the dipole, but around -32dB. I did some checks and there did not appear to be any ill effects on other bands. So the ground wire has been permanently removed. Needless to say, by the time I had got this sorted out, 15m had closed!

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.

A good match

Out of all the discussion about whether the Elecraft K3 receiver is or isn't noisy, one thing that eventually became clear was that a lot depends on the speakers and headphones you are using. I found that my K3 sounded much better when I tried a pair of Sennheiser HD-485 headphones that I'd bought for music listening, which had an impedance of 32 ohms compared with the 8 ohms of the old pair I'd been using. The passive communications speakers I was using sounded shrill and lacking in bass compared to the computer speakers I'd used before. However, my attempts to find powered computer speakers that were RFI proof by trial and error had turned out to be rather costly.

This afternoon I walked down to Aldi with Olga to get some shopping and, after some hesitation, decided to take a chance on a pair of Medion Multimedia PC Speakers that were being sold there for £7.99. Aldi offers a 30-day no-quibble refund if you aren't happy with something, so if the usual rasping noises occurred when I spoke into the mic I could easily take them back.

The Medion speakers sound very good when plugged in to the rear speaker socket of the K3. They have a very effective tone control that completely eliminates any tiring noise or hiss in the fully clockwise position, and they can provide plenty of bass for "armchair listening." What's more, I found them completely free of any RF breakthrough when running 100 watts of SSB to my attic antennas which are directly above the shack - a tougher test than they'll experience in most shacks, I'll bet.

I think the modern styling of these speakers suits the Elecraft K3, and the black and silver finish matches my Heil desk mic and my Bencher straight key very nicely.

Another good point about these speakers is that they run off 14V DC from an external adapter with a standard barrel type plug. This means that you can easily power them from your shack power supply and avoid the need for another power-consuming wall-wart. A 14V 800mA unregulated analogue wall-wart power supply is provided, and could probably find a use in another project - you'd pay £4 or more for that alone at Maplin.

Whether you need some external speakers for your radio or some RFI-proof speakers for your computer (or a neighbour's) these Medion Multimedia PC Speakers look like a good investment.

Geminids

I switched on the computer just after 10pm and saw Roger G3XBM's post about the Geminid meteor shower, so I set the K3 to 50.230MHz JT6m, put on a warm coat and went outside to take a look. The radio didn't receive anything but in the space of about 15 minutes I saw three bright, slow moving meteors.

I have had a moderate interest in astronomy all my life. In fact, there is a small Celestron telescope occupying a valuable corner of the already cramped G4ILO shack which I have been intending for months to put back in its box and put up in the loft because it hasn't been used for at least three years. The main reason, apart from the Cumbrian weather, is that we are surrounded on all sides by street lamps (not to mention the neighbours' security lamps) which makes any real enjoyment of the night sky impossible.

Directly at the back of the house are two orange sodium lamps, but I noticed for the first time this evening that another lamp down the road had been replaced by a brighter reddish-white kind of lamp that was even worse and killed any chance of seeing stars in the northerly direction.

I had an unhappy thought. Astronomy enthusiasts, whom I believe to be more numerous than radio amateurs, have failed to convince councils to install downward-focussed non-light polluting types of street lamps that would not interfere with viewing the night sky, so what hope have we of persuading the powers that be to outlaw devices that interfere with radio reception?

Spectrum Defence Fund

I'm glad to see the RSGB has taken up my suggestion and opened a Spectrum Defence Fund to enable radio amateurs to contribute towards a legal challenge to the attitude of the UK authorities over interfering equipment such as power line networking devices. You can contribute by writing a cheque, payable to the 'Spectrum Defence Fund' and sending it to Spectrum Defence, RSGB, 3 Abbey Court, Fraser Road, Priory Business Park, Bedford, MK44 3WH.

I have written to the RSGB strongly urging them to make available a page where online donations can be made. This would allow websites such as this one to further support the cause by writing articles on the subject and publishing links to the donation page. I am sure this would result in donations from a great many people who would not otherwise be aware of the campaign, possibly even from outside the UK.

If you have a website and would be interested to support the RSGB Spectrum Defence Fund in this way, please write to the RSGB as well to support the case for an online donation page.

Wi-fi interference

I have often complained about the increasing amount of radio interference and its effect on amateur radio operation. But it is not just ham radio that is affected. Other wireless devices are too. The latest problem of this type that I encountered concerns a wi-fi internet radio called the MagicBox IMP Adapt.

My wife and I enjoy listening to classical music. One day some time ago I was trying out some internet radio tuner software and discovered several stations online that played non-stop classical music with few announcements. One that I particularly liked was WCPE, TheClassicalStation.org from North Carolina. I wanted to listen to it through the hi-fi system instead of the computer speakers so I bought an IMP Adapter, a dedicated "internet radio".

The IMP worked fine for a year or so but the other day it started freezing at "Initializing network" and then apparently rebooting. I wondered if it needed a firmware update but none was available. I did a bit of Googling about the problem and discovered several interesting things about it. Apparently this and most of the other wi-fi internet radio devices on the market are not specially designed custom electronics as you might expect, but general purpose computers with ARM processors running Linux! And a group of clever people called the Sharpfin Project had developed a system to enable you to bootstrap later versions of the software designed for other models of internet radio, even though they are no longer available from the original manufacturer.

This didn't help me much, because in order to bootstrap new software on to the device I needed it to connect to the network, and it wouldn't. But I discovered that the firmware wasn't the cause of the problem anyway. As you can see if you take the thing apart, the little embedded computer has a USB socket on it, and plugged into that is a bog standard USB wi-fi adapter. Apparently the one used with the IMP Adapt falls over in the presence of the latest IEE 802.11n wi-fi signals, which are becoming increasingly common being supported by the free wi-fi routers being given out by all the major broadband providers.

When I first moved here, only geeks had home networks. I never even bothered encrypting or securing my wireless network as the neighbours are mainly retired people or had no interest in computers and the likelihood of them trying to hack into my computers seemed negligible. Today if you open the "view all wireless networks" window on my laptop you have to scroll down to see them all. Obviously my wireless adapters are struggling to receive my network's signal among all the competing signals. In fact, I've just ordered a pair of 10dB gain wi-fi antennas for my router.

But back to the IMP Adapt. I found that there is a simple and fairly inexpensive solution to the rebooting problem, and that is to replace the existing USB wi-fi adapter with a different model. There is no guarantee that any old USB adapter will work with the drivers in the IMP's Linux kernel. But I discovered that the Edimax EW-7318UG adapter will work. It's also cheap - currently £7.99 from play.com - so it was worth a try. I ordered one, it came this morning, I fitted it and now the IMP connects with no trouble and works as well as it did originally. I had an anxious moment as it didn't look as if it would fit in. But I found that you can remove the plastic cover leaving the bare circuit board and then it fits in perfectly.

Now that the radio had network connectivity I used the Sharpfin software to install a newer firmware that provides a few extra features. So now not only can I listen to WCPE The Classical Station on the hi-fi again, I can also control the radio using a web browser, and telnet into it and change configuration settings. I could even write programs using free software tools and run them on it. Not that I particularly want to, but it does show that the IMP Adapt really is a little Linux computer.

I expect a lot of these IMP adapters and others that use the same 802.11n-incompatible wi-fi adapter are thrown away because they don't work any more. If you come across one, it might be worth salvaging. I'm sure someone could think of other uses for a little Linux computer with a three line LCD display, a network interface and a stereo audio output.

Reprieve for 40

Things are not quite as dire at G4ILO's Shack as I reported a week ago. Although the noise on 20m is still as bad as it was, the use of resonant noise antennas does allow me to null it out on most of the band, though the noise (and my ability to eliminate it) does seem to change from day to day.

The noise is still bad on 80m as well. I only had limited capability on 80 anyway because the bandwidth of my short dipole is so small, centered around 3580KHz. However, it picks up the noise pretty well. It's hard to get as much noise on the noise antenna so I have not found it very easy to null it out. So I think 80m may be a goner.

Curiously, 40m does not seem to be affected much at all. I have a choice of a linear loaded dipole or the MFJ magnetic loop on 40m, though the magnetic loop outperforms the dipole so that's what I mostly use. In the evening I get an S7 noise level on either antenna, which is probably not bad for an indoor antenna in an urban location. More importantly, it's not the awful sparky crackly noise I get on 20 or 80, so it's possible to listen to the band. In fact, I can receive signals on 40m quite well. This evening on PSK31 I heard (and worked) on the magnetic loop RA4HDT who is almost in Asiatic Russia, and while I was typing this Fldigi's PSK Reporter decoded PY2RD in Brazil.

Desperate strokes

Still fighting the QRN here, though the nature and strength of it keeps changing, making it hard to assess the effectiveness of different sense antennas for the MFJ 1026 noise canceler. I'm currently using a SuperAntennas MP-1 for the noise antenna. It's fiddly to adjust, as always, but when tuned correctly it pulls in a big noise signal on 20m which enables me to cancel the noise very effectively.

It is no help at all on 80m though. I think I'll just have to abandon that band. My short dipole has a pretty narrow bandwidth and is not all that much use on 80m anyway,

QRT

I suppose it had to happen eventually. I've been battling noise on HF for some time. For several weeks the MFJ-1026 had been doing a good job of eliminating it on 20m. But recently the noise seemed to be changing, such that I often could not eliminate it entirely. This evening I noticed it had suddenly got much stronger. Perhaps the metal framework of the conservatory that has been erected today is reflecting the noise from many different directions. Whatever the reason I now have S9+20 noise on all bands from 20m and down (I didn't try the higher ones), I cannot eliminate it, and operation on the HF bands is now completely impossible. The picture shows the noise level, right now, on 80m.

Here is a sound clip of the noise on 80m. The sound actually varies depending on what frequency you're on. At one part of the band it sounds a lot like car ignition interference, and the K3 noise blanker knocks it down to a "mere" S8 or so. But at other frequencies nothing will touch it.

Having experienced, through Internet remote operating, just what a difference it makes having decent antennas, I think the time has come to give up trying to operate from here. The results just aren't worth fighting for. The only bands that are free enough of interference to use, 10m and up, are dead most of the time. I love those bands when they are open, but they aren't open often enough to make a viable hobby.

Moving house isn't an option. My wife doesn't want to move, despite the recent friction with one of our neighbours.

What I would like to do is set up an Internet remote with a group of other similarly QTH-challenged UK amateurs. However, this would require a significant investment in time, money and effort and I don't know whether there are enough other people with sufficient of all three plus the motivation to make this happen. Nor do I know how to contact them. I could try writing to RadCom, but I'd probably get a lot of time-wasters who'd like to use something like that but have nothing to contribute. It would be simpler just to subscribe to one of the existing remote club stations, use that when I want to do some operating, and sell my own equipment.

Whatever happens, it looks like being the end of operations from G4ILO's Shack as I currently know it.

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.