Digital Signal Processing

The Norwegian-language "The road to the international radio amateur license" came off the press this June. It is based on the RGSB International Amateur Radio Examination Manual from 2006, which RSGB graciously allowed us to use.

But the translation has been adapted on several topics. One example is the chapter on propagation due to the need in our country for more emphasis on propagation in polar regions and in mountainous terrain. Another is a completely new chapter on digital signal processing.

I got involved quite late in the project for this new chapter. The importance of digital signal processing in amateur radio has just kept on increasing as variable digital filters, adaptive noise reduction filters, adaptive notch filters, digital demodulation, and software defined receivers are everywhere.

The entire book project was handled by the Bergen group of the Assocation of Radio Amateurs in Norway. In fact it was done in order to celebrate their 90 year anniversary. The editor has been Frode Igland, LA6VQ.

My efforts resulted in a completely new chapter which was written during the first few months of this year. It was finalized with valuable input from the editor after a process of sending the manuscript back and forth lots of times. It was a fun project, where the challenge was to convey complex ideas with a minimum of equations.

The chapter has these headings:
  1. Applications of digital signal processing 
  2. Discrete values
  3. Quantization - digitization of amplitude
  4. Sampling - digitization of time
    • Aliasing
    • Nyquist frequency
    • Reconstruction filters
    • The time domain
  5. The frequency domain
    • The Fourier transform
    • The Fast Fourier Transform (FFT)
  6. Digital Filters
    • Moving average as an example of an FIR filter
    • IIR filter equivalent of a low pass RC-filter
    • IIR filter equivalent of a high pass CR-filter
  7. Example of a software defined receiver with spectral display
The final section briefly discusses the RTL-SDR and uses an example from this blog showing activity of secondary users in the 70 cm band as shown here.

Sverre Holm, LA3ZA, is a regular contributor to and writes from Norway. Contact him at [email protected].

Why the XiOne SDR receiver is different (in a good way!)

We’ve talked a lot about the various Software Defined Radio (SDR) USB dongles that have popped up over the last couple of years. I own several and have often played around with them. They suffer a bit of a flaw in the fact that they connect directly to the computer via USB which isn’t ideal because my computer room isn’t the ideal RF environment.

The advantage of the XiOne is that it has the capability of connecting to your home network allowing you to use a computer/tablet/phone that network to operate it. You can locate it away from RF interference sources and either use the XiOne’s Wi-Fi or run ethernet to connect it back to your router. Very cool. That’s why I think the XiOne’s Indigogo campaign from a German company called XiVero is worth looking at.


As of this writing, they still have 35 out of 100 of their specially priced (US$139) slots left. If you’re interested, might be worth a look. If they can get enough funding momentum, this looks to possibly be a very popular little receiver.

Matt, W1MST, is the editor of

On Making Nanowaves – Part 4

Researching suitable LEDs for our lightwave project forced me, once again, to the bottom of the learning curve. Like the variety of photodiodes being used in simple lightwave systems, there were a myriad of LEDs experimentally lighting up the skies both in the UK and in the U.S.

It seemed that the present flavor-of-the-day in terms of LEDs was the Luxeon III, a 3W / 1.4A device being produced by Phillips.....or rather.....was being produced. Apparently our new found interest in lightwave communications had been coincidental with the retirement of this popular LED and all stock had been depleted! Although still available in some wavelengths, there were none in the desired 'deep red' portion of the spectrum that we had chosen for our system.


All was not lost however as a 'replacement', largely untested by the lightwave community, spec'd-out at a lower power but with a somewhat more efficient design. The new device was the Luxeon 'Red Rebel' and rated at 700ma. ....apparently no slouch at all.

I had also been watching the various offerings available on e-bay which provided a number of tantalizingly inexpensive options. Many of the LEDs from China appeared to offer good promise and may well be good performers, but most appeared to be lower-quality knock-offs of the name-brand models.

These higher-powered LEDs, on close examination, usually contained two or more separate LED die behind the lens. A single light source is required to achieve maximum focusing / lens illumination efficiency and although tempting, should probably be avoided. 'Safe' names to look for include Philips, Osram and Luminus and often, bargains can be found on e-bay when NOS is being disposed of.

Like most 'power' LEDs, the Rebel needs to be mounted on a heatsink otherwise catastrophic destruction would be immediate. The usual method of heatsinking is to attach the LED (by solder or adhesive) to a copper star-shaped interface which is then fastened to a small heatsink.

The interfaces can be purchased separately but soldering the LED can be challenging without overheating it. They can also be fastened with JB Weld and enough pressure to ensure a firm bond without damaging the LED. An easier alternative is to procure the LED already mounted on the interface as shown here.

Once adequately heat-sunk, voltage can be applied to the LED after taking measures to limit the current to safe levels. Although these LEDs are very small, they emit an exceptionally bright light and must be treated with care. The Rebel is shown here, shortly after first applying voltage. The current in this test was just 100ma. Although they are rated at 700ma, I have run this one up to 1A without failure but it is normally run at the rated current.

Luxeon Red Rebel at 100ma.
The next task was to tackle the 'antenna' which, in a lightwave system, is the lens. Many of the UK amateurs were having good results with inexpensive 4"-5" magnifiers mounted inside ABS or PVC tubing. The remainder, and those in the U.S., were using plastic Fresnel lenses mounted in homebuilt plywood boxes of various designs. Clint's (KA7OEI) website contains a vast amount of valuable hands-on info describing the latter and we chose to go via that route.

Like the large variety of both photodiode and LED selections, fresnels were no different. Once again there was a lot of information to digest while learning about the various types. Eventually, John, Markus and myself each purchased two plastic fresnel lenses from 3DLens in Taiwan. One would be used in the receiver box while the other was for the transmitter. These were 26cm square lenses, model A260.

Unfortunately I no longer see these particular lenses being offered....hopefully it is only a momentary depletion of stock. There are many different sizes and types of fresnels out there....some if them perfect for this type of use and others not so good, so think carefully before buying anything and know what you are getting. Studying Clint's pages regarding fresnels will help immensely.

Things to pay attention to are the focal length and groove 'pitch'. For a typical 10"-12" lens, look for something around 10-12" focal length, otherwise the mounting enclosure will get too deep and awkward to handle. Front surface 'groove pitch' should not be too fine...something around .5mm is good but our finer (.2mm) seemed to work well also.

Now that the LED had been mounted and the fresnel lenses were in hand, the next task would involve the focusing mechanism and alignment. Thankfully John had devised a smart method for mounting and adjusting focus a few weeks earlier, when we were still working on receivers.....

Steve McDonald, VE7SL, is a regular contributor to and writes from British Columbia, Canada. Contact him at [email protected].

Ol’ Sol slowing down?

Looks like we’re headed directly for a period of minimal solar activity:

And here’s a related article from the Helsinki Times:

The video was brought to my attention by Don K2DSV.  IF the hypothesis of the video is correct, lower ionospheric activity would be the least of our worries.

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

Larry Makoski, W2LJ, is a regular contributor to and writes from New Jersey, USA. Contact him at [email protected].

Getting there

As opposed to probably a majority of you, I am SO far behind the times from a technological point of view.  I still do a majority of my logging with paper and pencil before I manually enter the information to my logging software.

When it comes to QRP Sprints or the Fox Hunts, most of my compatriots use N1MM or some such program.  Again, I still use paper and pencil. I feel that I am lucky to be able to walk and chew gum at the same time. Operating a radio and trying to computer log simultaneously during a Sprint or a Hunt used to send shivers up and down my spine.

But I am getting better.  As long as I am not furiously trying to keep up with a pileup of QSOs in the midst of a frenzy during a Sprint or a Hunt, I have trained myself to log and operate at the same time (See? You CAN teach old dogs new tricks!). I recently purchased a small keyboard for my Nexus 7, so that I can log during casual portable ops without the need for pencil and paper. It cost me all of 8 smackers on eBay.

That’s Ham Log that I keep on there, which in and of itself is a great piece of logging software for Android. The problem was that it’s always been a pain in the butt to use the Nexus touchpad keyboard, which caused me to “one-finger” type, and slowed me down, holding me back.  So for the longest time, I was doing the same thing – logging on paper and entering the data later, at my leisure (which makes no sense). This “tactile feel” keyboard brings a lot of familiarity and works a whole lot better for me, and now I am actually able to use the Nexus 7 for logging in real time (sometimes).  I know that it’s pathetic, but while I am able to use this setup for general QSOing, the melee of contests or Fox Hunts drives me back to the security of “old technology”.

I guess the next step will be to install the KX3 Companion app.  Boy, that will be like Star Trek for me!

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

Larry Makoski, W2LJ, is a regular contributor to and writes from New Jersey, USA. Contact him at [email protected].

Think I will meet the deadline

I have imposed a deadline for myself with regards to Skeeter Hunt results. I want to have both the “scorecard” and the soapbox published to the Skeeter Hunt website this coming Sunday, after the log submissions deadline.

The “scorecard” itself is a piece of cake.  It’s simply an Excel spreadsheet that I have composed, with formulas that do all the menial calculating chores for me.  I simply plug in the values and the spreadsheet calculates the final score for me. I will upload the completed spreadsheet to Google Sheets and it will be available for all to see on the Web, once it’s completed. This was a good exercise for me, as I was very weak with regards to using formulas in Excel. I’m still no expert by any means, but I know a lot more than I used to, which was practically nil.

The soapbox page is another animal.  That is “simple” HTML composition, but it’s more time intensive. I have about one half of the soapbox comments and pictures placed on the unpublished Web page.  At the rate I am going, if I can add about 5 more soapbox comments to the page each evening, over the next 4 or 5 evenings, it will be ready for publishing on time.

All this leads me to a worrisome discovery.  This year we had a record number of Skeeters sign up.  But I am lagging behind in receiving log summaries. Last year I received a total of 71 summaries. As of this minute, I have only received 54. I guess a “Que Sera, Sera” attitude is in order, but I sure would love to see more log summaries submitted.

It’s very important to me that these results get published on time this coming Sunday.  You folks are kind enough to participate, and I know how much you like to see results.  I do myself!  It’s not so important for me to see where I place, I want to see how my friends did, what their setup looked like, and I like to read about the fun they had.  The results and soapbox are a crucial part of any of these “special” QRP events, in my most humble opinion.  No one wants to make an effort and then wait months or more to see how things stacked up.

So, God willing and the creek don’t rise, you’ll see the finished results this Sunday at
I am just hoping I get a few more log summaries and soapbox comments before then.

And then the final phase will begin, which is the certificates.  I have to give myself more time for those, but hopefully, everyone who will qualify for one will have it by the end of September.

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

Larry Makoski, W2LJ, is a regular contributor to and writes from New Jersey, USA. Contact him at [email protected].


It’s evident that we are now on the down side of the peak of Cycle 24.  For the most part, I have had superb conditions for working DX during my lunch time QRP sessions for the past 17 months. DX has been plentiful, with good signals and decent RSTs on both ends. 17, 15 and sometimes even 12 Meters have been happy hunting grounds.  There have even been smatterings of openings on 10 Meters, which is not often the case during the 1700-1800 UTC weekday time frame.

I still hear DX signals on 17 Meters, but they’re not as strong or as plentiful as they were. 15 Meters is nowhere near as nice as it was just a few months ago.  It wasn’t so long ago that I was working three or four different DX stations during my lunch break – and it seemed like all areas of the world were open at the same time! I think that the days of working the world “with 5 Watts to a wet string” are just about over – as far as Cycle 24 is concerned, anyway.

With band conditions changing, it seems that lately, more and more of my lunch QSOs have been domestic – not that there’s anything wrong with that!  Today, I was saved from being shut out at lunchtime by Jim K4AHO, who answered my CQ on 20 Meters.  We had a nice chat that was not only 2X QRP, but was also 2X KX3.  Jim was using a dipole and I was using the Buddistick, of course.  QSB was a bit of a nuisance. At the fading’s worst, Jim was 459, and at best he was 579 (which he was for most of the QSO).

In addition to the declining ionospheric conditions, the weather here in New Jersey this Summer has been less “Summer-y” than I was looking forward to.  Take this morning for instance. When I woke up this morning, the thermometer was displaying an outdoor temperature of 52F (11C).  Very strange for August 18th.  That’s almost unheard of, any other year. On the whole, it’s been an average to dry Summer and the temperatures have been down and the humidity has been way down compared to the past three or four Summers.  The number of days that we have reached or have gone above 90F (32C), can be counted on both hands. There have not been many hazy, humid, hot days (The Dog Days of Summer) this year at all.

The weather people on TV have been saying that we are experiencing is an “average” Summer for this part of the country. The past few have been hotter than normal, so that’s why this one feels so strangly cool. After the Winter we had last year, I was really looking forward to the heat.  I guess there’s still time for us to get some hot days, but I saw on the website that the Northeast and the upper Midwest are supposed to experience a Polar Vortex in mid September, bringing along temperatures closer to what we might expect in mid to late November. Brrrrrr.

The other day, while walking my beagle Harold, I noticed the oak trees in the neighborhood are already shedding their acorns. That’s not a great sign as the trees did the same thing around this time last year and we had a terrible Winter.  Normally, the acorns don’t start falling until mid to late September around these parts.  The squirrels will have extra time to store up food for the Winter, and we’ll probably have another long, cold one.  Oh well, at least conditions on 160 and 80 Meters will probably be good. You always have to look for the silver lining and try not to think about the heating bill!

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

Larry Makoski, W2LJ, is a regular contributor to and writes from New Jersey, USA. Contact him at [email protected].

Portable in a very windy Cumbria

Before amateur radio took over my life my main pastime was competing at dog agility which I did moderately successfully for many years, for several of those I was even the chairman of a Nottingham Agility Dog Training Club and organised one of the larger Kennel Club Championship shows as well as judging at many events. If you search my YouTube page there are a number of videos showing me and the dogs in action.

Things change and sadly I became disillusioned with the sport as seemingly endless rule changes and its increasing popularity saw it losing its core ideal, what was meant to be fun for dog and handler had sadly become too competitive, professional and commercial, too many people now make money out of the sport and what was once an enjoyable social activity is now spoilt by unsportsmanlike behaviour, complaints and bitchiness.

When my dog Boris suffered a cruciate injury the enforced time-out made me realise I didn't want to do it anymore and so I don't.. well apart from the odd exception, last weekend was the West Lakes Agility Club Show held in the small town of Haverigg on the Cumbria peninsula (Locator IO84IE)

This is a lovely old-style small friendly show with the bonus of being held just a stones throw from the sand dunes and beach. I had agreed to go and like the recent holiday in Skye it was initially planned with no thought for any radio operating.

We would be caravanning at the show for the best part of four days without any electrical hookup and the wife had volunteered to help on Saturday leaving me on my own for most of the day... so a plan was hatched at the last minute.

I purchased a nice new 'spare' 100A/h leisure battery and smuggled on board the FT-857D with some suitable battery clips, headphones, a fiberglass pole, some antennas. I don't own a suitable 'portable' ATU at present,  having borrowed one from SKARS on several occasions but as this was a last minute thing I would have to chance operating without it. I took the M0CVO HW-20P OCF-Dipole, which has a usable VSWR on 20m, 17m, 15m, 12m and 10m without an antenna tuner and the M0CVO Magitenna, but wasn't sure what I would get from this as I'd only ever used it with a ATU.

The weather was difficult all weekend, we arrived on the Friday to be met with warm and sunny conditions but a steady strong wind. There was bit of a battle to get the caravan awning up but we managed it.Saturday the wind just got stronger, the forecast for Sunday was for even stronger winds so it was dismantled and packed away, indeed it was worse around 25-30mph with must stronger gusts.

Undeterred I got the antennas up,  however the fiberglass pole I have must be getting on for 10 years old, and would often fly a pirate flag when camped at agility shows. It had already lost it's top section many moons ago but was still quite tall and so I hoisted up the OCFD balun and coax and the end of the magitenna wire in the buffeting wind and it was swinging around wildly - almost inevitably it proved too much and the remaining top section splintered!

Despite losing over in a metre in length I tried again and managed to get everything up, the OCFD wires were tied out to form a sort of inverted-vee using a handy nearby fence, the Magintenna was pulled to form a sloper across over the front of the caravan, but due to the lost height actually touched the front of the roof. Amazingly I got an almost 1:1 VSWR on 40m and loud and clear RX.    

This weekend was the International Lighthouse and Lightship Weekend (ILLW) this annual event has been going since 1995 and promote public awareness of lighthouses and lightships and their need for preservation and restoration, and at the same time to promote amateur radio and to foster International goodwill.

The bands were kind and I had an enjoyable Saturday afternoon and a few hours on Sunday making QSOs with a number of UK and European lighthouse stations on 40m and 20m and it seems the whole event was a great success. Alas the wind proved too much for the remainder of the fiberglass pole and it developed a large crack in the bottom section forcing me off the air.

By coincidence Haverigg has two lights, the old Hodbarrow beacon and the restored Hodbarrow Point lighthouse (pictured above from the beach). Last year we walked to the restored lighthouse but since the restoration was completed in 2004 it is sadly looking in need of some remedial work.

I only learned of the ILLW event at the last minute and sadly neither of the Haverigg lights were activated that weekend, next year if the show is on at the same time I may look at trying to operate from them.

Oh and the wind? Here is a video of a walk on the beach on the Sunday morning..

Andrew Garratt, M6GTG, is a regular contributor to and writes from East Midlands, England. Contact him at [email protected].

e-Bay PCB Thermal Transfer Paper

This past weekend I had the first opportunity to try my e-Bay purchased thermal transfer paper. It was to be used in my iron-on PCB work as a hopeful improvement over what I had been using...just ordinary printer paper. Supposedly the shiny photo quality papers were proving to be good performers but are expensive. Some have reported good results with glossy magazine paper but my one experience with that was not a pleasant one. Unknowingly, when I had removed the magazine page, a small amount of the sticky adhesive used in the binding process was still on the sheet. Running it through the printer caused it to melt and smear some of the laser cartridge's toner and for the next several weeks, any printing I did had a slight black streak along one edge...doh!

My new paper from China (free shipping!) was pretty inexpensive and if it offered even a slight improvement, would be well worthwhile. This first use of the paper would be a circuit board for my earlier test-bed GW3UEP 630m transmitter. I had finished designing a PC pattern for it, using MS Paint, and was anxious to see the results.

I decided to use a small separate board for the crystal oscillator-divider so at a later time I could more easily swap it out for a DDS driver. Using a separate board would allow me to do that without disturbing the rest of the transmitter.

I know that a lot of folks turn up their noses at MS Paint but I have always found it to be a very versatile piece of software and have used it for making PC layouts for many years. I also use it for drawing all of the schematics appearing on my website.

After printing the pattern (printer set for maximum resolution and darkest print) and ironing-on the pattern , I allowed the board to cool for several minutes before immersing it, along with the now firmly attached yellow paper, into cold water. The first thing I noticed was how easily the paper came away from the board. It actually 'un-peeled', much like a good quality price tag know.... the ones that don't take forever and come off in tiny bits and pieces. It peeled off smoothly with no paper residue left on the board. This was a huge improvement already. There were just a few traces of toner left on the paper as almost all had been transferred to the board.

Once dried, a close examination revealed that I had pressed a little too hard with the iron and there was some evidence of  'squeeze-out' along the edges of some lines. I also found one or two very small thinner areas that probably required going over with a permanent-ink black marker pen just to make sure that those spots did not get etched. Over all I was extremely pleased with the paper and will be using it from now on.

Another recent change in my PC etching regime has been a switch from the old Ferric Chloride standby to a combination of Hydrogen Peroxide and Muriatic acid. Not only does it seem to etch more cleanly (no undercutting) but it also etches very quickly and without any solution warming needed. This board was completely etched in just over 4 minutes.

The chemicals used in this method are inexpensive and are readily available at the drugstore and at the hardware store. There are numerous web-descriptions of this particular etching process but this site seems to cover the basics nicely.

The completed board turned out as shown here:

The CD4060 not only functions as a crystal oscillator but also as a versatile frequency divider. As well as fundamental frequency output, ten different 'divide-by' functions are available depending in which output pin is chosen. These range from divide-by 16,384 to divide-by 16. This circuit uses the latter, dividing the 7.6 MHz crystal down to 475 kHz at pin 7.

In summary, I can highly recommend the e-Bay yellow thermal transfer paper when used for this method of making PCB's and is much cheaper than buying photo-quality printing paper.

Steve McDonald, VE7SL, is a regular contributor to and writes from British Columbia, Canada. Contact him at [email protected].

Largely non-radio day

Son Chris and grandson Edward outside their home.
Although I shall probably go on 472kHz WSPR shortly, today has been a day largely without radio: we went on a train day return to Canterbury to see our son Chris and family. We have done this now 3 times and get about 4 hours with them. It was good.

Roger Lapthorn, G3XBM, is a regular contributor to and writes from Cambridge, England.

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