Posts Tagged ‘QRN’

The Dreaded Wall Wart

It seems that the ARRL has made it official ... well, maybe not, but at least Ed Hare, W1RFI has. In a recent interview on the HamRadioNow webcast, Hare said that he believed that switching-mode power supplies are a more common source of QRN than noisy power lines ... and I believe him. I have heard countless horror stories of amateurs having to go QRT for good (at least on HF) because of issues with neighbourhood switching supplies. It's one thing to be able to hunt these things down and remediate the problem within your own home but when it comes to the whole neighbourhood, it's an awfully large challenge. And it's not as if there's just the odd one around, here and there ... they are everywhere.

In Ed's own words:

 “The old days of those iron transformers are gone,” Hare said. “Every single one of these is a switcher. We’re also seeing noise from pulse-width control motors.” Hare said the big culprits are “little wall warts,” not switching supplies designed to power Amateur Radio gear. “Every TV you own has a built-in switcher, almost every device has a wall-wart, and a lot of these are imported, not necessarily meeting the FCC rules, so we’re seeing more reports involving those.”

I've never personally had a problem with a wall wart, other than a cheap charger for my I-Pad, but that's not to say I haven't run into switchers. The charger emitted a low-level hash that I could hear only on a very quiet 6m band, not much of a real problem considering that I could unplug it at any time. A couple of problems here in the neighbourhood were eventually traced to the poorly designed or faulty switchers inside some CFL bulbs. These were emitting signals via the powerlines and being picked up by my antennas almost two blocks away. This was a problem only on LF however, where the powerlines make pretty efficient antennas.

Hare went on to say that some of the new LED-type lightbulbs have proven to be noisy as well. Not hard to understand when each one has its own low voltage switching power supply. What is hard to understand is why these device are even allowed on the market without having to undergo some type of noise-testing for approval. Another 'growing' threat are the lights used by neighbourhood grow-ops, legal or otherwise.

Hare also indicated that the ARRL lab can work with manufacturers to correct problems but that they need to know specific model numbers and information about the problems you are experiencing with the device.

Apparently, according to Hare, many issues can be resolved without involving enforcement from the FCC, the last step, should issues not be resolved by other methods.

You may be able to help by sending the needed information to the ARRL Laboratory for this and other types of RFI. Both Ed Hare and ARRL EMC Specialist Mike Gruber, should be contacted if you can supply information or have an unresolved problem.

The excellent 11-minute interview (Episode 196 'W1RFI's Tall Tales from the ARRL Lab') can be watched here, with thanks to HamRadioNow TV and to Gary Pearce, KN4AQ of HamRadioNow.

Noises Off – WiMo QRM Eliminator

As I posted at the end of June I was almost on the point of giving up on HF due to the high levels of QRN/M suffered at home.

In desperation I had been looking at some of the noise cancellers available from MFJ and others. I had heard conflicting options on their effectiveness but was willing to try one if I could obtain one cheaply. The MFJ units are in my opinion expensive to purchase new so I bid on several that came up second hand on eBay but they invariably also went for silly money. I was even contemplating building an home-brew one from the numerous designs available.

Then I discovered the WiMo QRM Eliminator, made by the German company WiMo Antennas and Electronics. Several online reviews and numerous YouTube videos seemed to indicate its effectiveness and taking up the then summer discount offer I ordered one for the princely sum of €147 including postage, around £116.

Due to heavy demand and low stock levels following the International Ham Radio Exhibition at Friedrichshafen I was told the unit wouldn't be available till the middle of August, so I was pleasantly surprised when the unit turned up last Friday morning.
I have connected it up and briefly tried it out and am impressed, as this video illustrates.

Even using one for a short time I would agree that they are something of a black art to set up and use and can understand why people might consider them useless, but this may be due to lack of understanding of how they work.

I have created a diagram showing a typical scenario.

The operators main antenna is designed to pick up distant signals, not necessarily DX but signals not emanating from the immediate vicinity, however they will also pick up locally produced QRM as shown, perhaps generated by a neighbours TV or PLT device. 

The QRM eliminator has a second antenna which isn't as efficient as the main antenna and ideally just receives the local QRM at a similar level to the main antenna. The device then takes this second signal and inverts the phase so when it is mixed with the main antenna signal the QRM is cancelled out.

The principal is quite simple, if you take two in phase signals and combine them you will end up with a signal with a larger amplitude. However if the signal is 180 degrees out of phase, the positive and negatives of the waveform cancel each other, producing a null signal. 

The tricky part is making sure the noise antenna just picks up the noise, if it picks up the main signal then that will also be cancelled out. The WiMo unit has three controls a gain and two phase controls it is a case of altering all three to maximise the cancelling effect without losing the main signal.

At present I just have several meters of wire running as the noise antenna along the side of the shack and this seems to fairly effective.

The unit is powered from 12V and can be left in line, but requires the PTT/TX-GND signal from the CAT/Linear socket from the transceiver to activate a bypass when transmitting and I don't have the appropriate 8-pin plug at present. If the unit is powered off the bypass is automatically engaged.

All in all, first impressions are good and looks like a worthwhile purchase.

Noises Off!

Radio frequency interference (RFI) is the bane of a lot of amateur radio operators. Sadly it is becoming a real issue at my QTH.

RFI is referred to as QRM or QRN and I am learning the difference.

QRM means "I being interfered with" and is interference coming from someone using radio equipment. This covers deliberate jamming, people tuning up or just normal operations on a crowded band that causes QRM.

QRN means "I am troubled by static" and technically means interference from a natural noises but has come to refer to interference coming from anything that is not an intentional radio emission and interferes with reception of transmissions. So now covers atmospheric noise, static or the noise generated by electronic devices.

Noise isn't a new issue here as I have posted before. It has tended to be sporadic and bearable but since becoming licensed I have become more sensitised to it. Until now I have tended to focus on the VHF/UHF side mainly contesting venturing only briefly onto HF.

My HF set up is limited at the moment with just a single antenna which isn't optimal for the lower bands. Due to the day job I am largely restricted to evening/night time operation when the upper bands have largely been closed anyway so haven't really attacked HF with much enthusiasm apart from data modes such as JT65 and WSPR which have immunity to noise.

When I have got the chance for some early morning daytime operation or at the weekend I have struggled with noise.  Recent weekends have seen some special event stations operating for the Museums On The Air and the GB1JSS Summer Solstice which have been predominately on the 40M band but I just cannot hear anything on that band due to noise.

I am aware the Sun has been particular active recently producing a number of large flares and CMEs that have caused a number of radio blackouts, but this noise isn't due to atmospherics I am certain it is man made by one of neighbours.

I made this video last weekend

and this video was from the weekend before that

This weekend was the 50MHz Trophy Contest which I was looking forward to, sadly it was also to become a victim of the QRN as this screenshot from my SDR will confirm, for much of the time I was operating I was just listening to noise.

I wasn't operating constantly, just grabbing a few minutes here and there and I did manage to make some decent contacts when the QRN subsided even catching some of the sporadic E opening to get EF7X in Spain.

I have ruled out any noise being generated by myself by powering everything off and running on battery. This leaves me in a bit of a quandary I could go around and locate and confront the culprit or even contact OFCOM but at the same time I don't want to antagonise anyone who could then object to any antennas I might want to put up in the garden.

Rotating the 6M Moxon around at the weekend during the contest as at least pointed me in the direction of one strong noise source. I am also convince that much of my problem is due to an evil PLT device in an adjacent property.

Following on from the weekend last night was the UKAC 50MHz contest and yet again I was troubled with noise leading to mostly local contacts.

I have been looking at some of the noise cancellers that are available from MFJ and others. I have heard conflicting options on their effectiveness but I am willing to try one if I can obtain one cheaply, or even home-brew one from the numerous designs available.

These devices work by using a second antenna which receives just the noise which is then mixed out of phase with the main antenna signal hence nullifying the noise. By all accounts they are tricky to use and often  need constant adjustment but may be my only viable solution at present.

Comfy chair

I picked up the office chair that I had ordered from Staples on Saturday. It is their Lockridge Manager’s chair which is currently on special. It normally goes for $89.99, but is $50.00 off for an online price of $39.99.

It is definitely filling the bill. I spent 90 minutes behind the key tonight hunting Foxes on 40 Meters. Not only did I bag two pelts, but when I got out of the chair to head upstairs, my back and hips gave nary a whimper. This sure is a far cry from that folding metal chair that I was using. When I would get out of that thing, I felt like I was ready for either a walker or a chiropractor.

Band conditions were so-so. Both Foxes were loud for a good portion of the hunt, but at times the QSB was tough to deal with.  I am also pretty sure both Foxes had high local QRN to deal with as each one was asking for multiple repeats of exchange information. Once again, persistence paid off and both Foxes were worked. Hats off to Paul K4FB and TJ W0EA.

I am going to be placing an order in the next few days with either Mouser or Jameco for some parts.  There are plans in the latest Sprat for a rather simple 40 Meter WSPR transmitter. I don’t plan to get too involved with the mode, but it looks like a rather easy build, and I am itching to really homebrew something.

I haven’t built anything in a while that wasn’t pre-kitted. I enjoy the process of buying and gathering the parts. From the looks of the article, this seems to be a project that lends itself well to perf board construction. I already have an ample supply of NE612s, so this will be a purchase of various needed resistors and capacitors, depending on whatever is not already in my junk box.

The final cost should be way under what I have seen some kit prices going for.

73 de Larry W2LJ
QRP – When you care to send the very least!

Switcher interference

I was tuning around the top end of 10m yesterday and noticed a lot of strong bubbly warbly noises, the unmistakable sound of switched mode power supply interference. It didn’t take long to track this down to the power supply for my QNAP TS-109 Turbo Station.

The TS-109 is a network attached storage device. But it is actually a small computer with a big hard drive, running Linux. I use it mainly as a backup drive for all our PCs, but it also hosts the shared documents folder so that we can easily exchange files from one computer to another. It runs a script that updates DynDNS when our IP address changes, which it does quite often at the moment. I could even run a web server on it if I wanted. So it really needs to run all the time. But the amount of interference it produces isn’t acceptable. I tried adding some clamp-on ferrite suppressors but they didn’t make much of a difference.

The power supply for this device is a plug mounted switched mode supply rated at 12V 3A. This is probably over-generous as the specification for the TS-109 gives the power consumption as 14.4W in operation. There are plenty of alternative 12V switched mode supplies available but I have no way of telling whether they would be better or worse than the manufacturer-supplied one as regards RF interference.

The only transformer based power supplies capable of supplying this sort of power are CB radio power supplies such as those sold by Maplin which have a 13.8V DC output. QNAP doesn’t, unfortunately, specify a voltage range for the Turbo Station so I don’t know if this higher voltage would be permissible. It would be very convenient if I could use the power supply I made for my QRP K2, which these days just keeps the K2’s battery charged up, but the output from that is 14.2V.

Switched mode power supplies really are the bane of the radio amateur’s life. I don’t know how to solve this problem at the moment, except to switch off the TS-109, which is inconvenient.

Noise generator

I heard nothing during my attempt last night to receive signals from KP4AO bounced off the moon. Nothing, that is, except a lot of noise. Sitting at the bottom of the garden with my newly constructed hand-held 6 element 70cm beam, the Moon was above and just to the left of the roof of our house. And the nearer I moved the beam to the house, the greater the noise. This house is truly a disaster area for radio reception!

This afternoon I thought I would try to see where the noise was coming from. With the beam horizontally polarized the noise was a broadband hash, white noise, indistinguishable from band noise except that its level is much greater with the beam pointing towards the house. If I turned the beam vertical then the white noise faded out almost to receiver noise, but another pulsing noise came up. It went kerchunk chunk chunk chunk, kerchunk chunk chunk chunk, ad nauseum. And the level of this noise peaked up with the beam pointing right at the shack window!

I switched everything off in the house and it made no impact on the noise whatever. I decided that it must be something battery powered. There is a radio controlled alarm system in the house that has a built-in backup battery. Nothing I can do about that. However I could not hear any noise increase when I went near it with the TH-F7E and a whip antenna. The noise level goes up and down as you walk about the house, as does the kerchunk chunk chunk noise, as if the noise source is invisible.

Eventually I did locate the source of the kerchunk chunk chunk noise. It was coming from an Ascot radio controlled clock sitting on the shelf in the shack just above my radios. I removed the batteries and after a few seconds the noise stopped. I walked about the house some more and in places I heard it again! This sort of thing can make you start to doubt your sanity.

Eventually I found that exactly the same noise was coming from another clock / weather station in our conservatory. It’s a different brand, not radio controlled, and (probably not coincidentally) it receives temperature and humidity readings from the same external sensor. Presumably they have some electronics in common and this is transmitting a signal in the 432MHz band.

But I haven’t found the source of the broadband hash, which may or may not be related to the crackly S9 noise that plagues most of the HF bands. I think the noise problems at this QTH are beyond solution. I haven’t logged an HF band contact from here since 13th March. It isn’t that I can’t work anything on HF from here, it’s just the demoralizing effect of hearing this dreadful noise as soon as you switch on and knowing that there are interesting signals buried under it that I have no chance of hearing.

Giving up the fight

Back in December I wrote that the RSGB had set up a Spectrum Defence Fund to enable radio amateurs to contribute towards the cost of a legal challenge to the UK spectrum management authority’s failure to take action over the interference caused by power line networking devices. Pleased to see some positive action being taken I made a donation and also posted links on my blog and website to encourage others to do the same.

Today I noticed, at the end of the RSGB Annual Report, the statement that “following advice from the Society’s solicitors … it was decided not to proceed at this time with any legal action.” So the RSGB has given up the fight and I have removed the links to the Spectrum Defence Fund from my website so that no-one else wastes any money on it.

Although PLT devices are a killer for any radio amateur unfortunate enough to live next door to one, it is clear from the noise at my own station and the comments I received from others with a similar problem that PLT is just the thick end of the wedge. A far greater number of short wave enthusiasts are having their enjoyment of HF ruined because of rising noise levels from a multiplicity of devices that individually would not be particularly intrusive. Whilst it is possible to track down and do something about a PLT installation, eliminating the noise that most of us in urban areas now experience from all directions would require the willingness of all neighbours to co-operate with finding the interference-generating devices and agreeing to replace them. This isn’t likely to happen. I fear the battle to keep the short wave bands free of interference is over and ham radio is a lost cause.

The only place to enjoy HF radio nowadays is out in the country, which unless you happen to live there means operating portable or mobile. The question is whether only being able to operate portable or mobile is enough to maintain most people’s enthusiasm? Although I recently enjoyed operating from my car on a couple of fine afternoons, it is no substitute for being able to go into the shack on a wet day or a winter evening and have a tune around and make a few contacts. I find I am turning on my K3 less and less often these days and when I do I often turn it off again soon afterwards without making any QSOs.

Will ham radio will still exist in ten years’ time? Many former short wave and FM radio stations now broadcast over the internet rather than the airwaves and I suspect that an increasing number of ham radio operators will end up doing the same. They will get worn down by the losing battle against electrical noise and antenna restrictions and be forced to swallow their objections and switch to online “virtual ionospheres” like QSONet and HamSphere (shown above) where there is no QRN. You only need to visit the HamSphere site to see the number of amateur license holders that have taken this step already.

The RSGB’s apparent acceptance that it can’t fight even a clear case of interference to short waves is clear evidence that this is a war we can’t win. Final surrender is just a matter of time.

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