James May would be proud!

When I was a kid there was a metalwork teacher at school who was a bit weird by the intellectual standards of your average teenager. This weirdness was exacerbated by one of the “cool” teachers Dr Jim, regaling the 6th Form chemistry class with tales of how Mr Metalwork had bought himself a patch of land, was living in a caravan on site and was building himself a timber framed house. This guy’s skill was even greater in that he was having to build the tools to cut the timber to build the house. This included a bench saw driven by a car engine to convert his raw timber into beams and planks. Impressive!

Now that was wasted on me in those days as a spotty oik, but today as an avid fan of Grand Designs, Kevin McCloud would be handing out awards with honours for that effort!

Where’s this going you ask? Good point and we’ll made! I’ve taken great delight in building the tools to make and test stuff as my interest in this field has grown rather than buying commercial off the shelf kit. Before I started playing with radio, one morning I woke up and decided to build a Geiger Counter. You what? Yup, a dyed-in-the-wool rad counting Geiger Counter!

Why? Well I’ve always had an interest in that area of physics and following the Fukushima disaster in 2011 there was a massive drive to provide the residents in the immediate and outlying affected areas with the ability to easily monitor the background radiation levels. A public spirited project then ensued with hundreds of easy build kits being shipped to Japan to help. As the immediacy of the situation dwindled these kit’s became available to others and I decided to have a look. Living on the south coast right next door to the home of the Royal Navy it would be interesting to see what was out there that’d make you glow in the dark! Let’s face it, when the local council sent the kids home from school with letters informing parents that schools now held stocks of potassium iodide tablets “just in case there was an “incident” involving the Dock Yard”, you’d guess that you may get a click or two above average off a Geiger Counter. Let’s face it they don’t run warships on AA batteries or unleaded!

So here is my Geiger Counter, equipped with a GM tube from deepest darkest Russia. You’ve got to love the entrepreneurs of the ex-Sov Block countries. I bet it was boosted from some military warehouse!


I can thoroughly recommend building one as a side project. If you want a go have a look here.

Now as part of this build I needed a reasonably accurate capacitance meter, so invested my money in one of these, from Roman Black.


It is one of the most useful bits of kit I’ve got and was worth the investment over and above the budget end of the market floating around on eBay. I try to look after it! The image doesn’t really do it justice I’m afraid.

So, you can imagine my horror when yesterday, while building my 1 Watter it all of a sudden started billowing clouds of blue smoke which very rapidly turned black and acrid!

James May moment and then some -“Oh cock!”

In my enthusiasm I hadn’t cleared sufficient space on my bench and had dragged the capacitance meter over an unfurled roll of solder which had shorted out the battery terminals on the PCB. To be honest I never realised 9 volts could generate that much smoke!

Thankfully after some very tender care Mr Capacitance meter is back and working.

Morals of the story.

1/ don’t dis your teachers at school

2/ value what you build even if it may appear trivial in the grand scheme of things

3/ keep your work bench clear!


A bit more test kit – RF Probe & Red Board CCCC

As with most things in life a change is as good as a rest. As I’ve been reading through the qrp-tech Yahoo group there’s been a host of information and advice regarding building QRP Kit especially the 1Watter and Rockmite ][.

Although I’m the proud owner of my homebrew oscilloscope a lot of the advice is geared towards those who don’t have access to that type of kit and that’s always a good thing. As such if you want to understand the advice, it’s worth having the tools at the lowest common denominator available. Enter the RF probe and the red board CCCC (Cheap Chinese Crystal Calibrator)!

I’ve been toying with the idea of building an RF probe for some time but basically couldn’t be bothered as I had no real need for one, but now I do! Originally I was looking at the plethora of hardcore homebrew ideas on t’internet but once again due to a poorly stocked garage/junk box I would have spent more money buying the bits to bodge in a true homebrew fashion than buying a prebuilt probe. Now that’s just not cricket as making stuff is 90% of the fun!

As a compromise Pacific Antenna’s kit was a reasonable investment and for once entered the country without Border Force inviting it into an interview room and probing it’s orifices and charging it a duty surcharge for the privilege! I’m of the growing opinion that being an amateur radio enthusiast would be better served by emigrating (not wishing to do a disservice to my fellow domestic enthusiasts, kit providers etc etc.) to somewhere warm! Cue Nathan Muir quote from Spy Game! (You can research that one yourself!)

Moving on before I get lynched, the RF Probe is a nifty little kit and if you’re starting out in this game and want a project for your Intermediate ticket, give it a look as it would tick the box for the practical build assessment and give you something in your arsenal if you want to build receivers/transmitters/transceivers at some point.


Not much for your money, but 15 minutes work gives you this


which plugs into your digital multimeter and gives you a useful diagnostic tool for future builds.

They even publish a How To Guide to assist you in getting to know your new toy.

The red board CCCC is another creature altogether. Chuck Adams K7QO who is the lead on the QSB-01 project hosts a site which is well worth a read where he uses the kit as an introduction to kit building as his first exercise.

Again, a simple build worthy of an Intermediate Licence project which gives you something worth having on your bench. When faced with a crystal, firstly don’t always believe what’s stamped on the housing of a crystal. Secondly, if it’s unmarked how do you know what it is? Thirdly, as builds progress in complexity you may be faced with the prospect of installing matched crystals in a transceiver to give a better IF (intermediate frequency).

By way of example, with the 1Watter build, at Phase 3 – Audio Detector Mixer (BFO) Installation, there’s advice to install three crystals from the supplied five which are closest in frequency. Now assuming all crystals are not made equally how do you tell who’s who from the innocuous metal cans? Further on there’s an advanced testing stage where the part built kit is tested against a crystal oscillator.

If you’re going to build something that works it’s worth giving yourself a fighting chance and for a whole £5 and a week/two week wait on delivery for a red board CCCC, on the scale of things it isn’t a bad investment.

Once again you get an assorted bag of goodies for your money.


Which with a little love and attention turns into this –


Here we are at the smoke test with a 12Mhz crystal under test and the board reporting everything correctly.

There is a need for a minor mod. In its native form this board is no good for crystals smaller than 10Mhz. By replacing a few capacitors with something more appropriate you will have a crystal calibrator more in tune to the frequencies utilised in all things amateur radio.

capacitor replacement CCCC

Soundcard Oscilloscope #2

Moving on from the previous post regarding the homebrew oscilloscope, I needed to build the calibration / signal generator unit to get the thing doing something other than reacting to mains pickup from the palm of my hand.

Mr Build Your Own Oscilloscope’s book has a nice chapter on how to do this. I won’t bore you with a death by photos, so here’s a select few –

The completed board prior to testing


Peak to peak voltage calibration


Testing prior to boxing


Boxed and completed


I wasn’t overly convinced by the Scope software’s signal generation, which was confirmed by unplugging my probes and watching a perfect sine wave continue uninterrupted on the screen! I’m chalking that up to not having read the manual for the program and a configuration issue because I dug out my other signal/function generator board which is an old Maplin Vellman kit, attached my scope probes and Bobs your uncle, it’s working an absolute treat.


Now I’ve got a fully functioning oscilloscope, with virtual knobs and dials! Once I get my head around the general functionality of an oscilloscope again (it’s been a long time since O Level Physics) hopefully that will translate across to the hideously complex device which is my DS203 and I can put that good use.


Soundcard Oscilloscope #1

Now this little side project is an absolute bonus on the scale of things and I would thoroughly recommend it to anyone playing with electronics or radio stuff.
There’s a minimum of test equipment you need to play this game and as you progress and your knowledge or lack of it grows there becomes a need to expand and diversify.
When I was trying to get my SoftRock working one suggestion was to monitor what was going on with an oscilloscope. It’s at that point you wish you had all the toys of a full blown R&D department on tap to make things easier!

When I was a kid I remember physics lessons when the teacher used to wheel out oscilloscopes on trolleys for lessons and they were the size of a detached house. That said they were always pretty cool in that they allowed you to see things which were completely abstract and were otherwise just drawn on a blackboard in the hope it would make sense.

A friend of mine who had a brain the size of a planet worked out how to link one to a then cutting edge BBC Microcomputer and get the oscilloscope to trace out keystrokes as they were pressed. Not bad for a 16 year old in the early 80’s! It was at that point I realised I had to have one. I had no useful purpose for one whatsoever but hey, what’s new there?

Things have moved on since then and now for a relatively small amount of money you can buy open source pocket oscilloscopes such as the DS203.


Moving up in price you can buy USB interfaced PC based units or go the whole hog and buy a second hand fully featured digital or cathode ray tube unit from eBay.

Now I’ve looked at these things over and over with no justification for expending the still not insignificant chunks of cash required (plus a fair amount on postage as a lab oscilloscope would be a suitable substitute on Britain’s Strongest Man for the Atlas Stones Challenge) for something that would get used a couple of times a year.

I very foolishly paid out for a DS203 off of eBay thinking it would be the way to go and then found that the lack of an English manual and a menu system that was so complicated meant I couldn’t use the damn thing! What I needed was something with knobs and dials which I could adjust like the old school ones!

Then one day I was internet surfing when I came across this.


It was a website plugging a cheap book (as it only exists as an e-publication via Kindle) on how to build a DIY soundcard oscilloscope probe.
I’d heard about these things before and dismissed the idea until I read further and found that the very simple premise, if utilised with the right piece of software, would give you a PC based oscilloscope that for all intents and purposes had knobs, dials, a screen you could easily read and more importantly a manual that actually explained how to use it!

The book is divide into 4 parts – the probe, a calibration and signal generator unit, how to use your newly built tools with Soundcard Oscilloscope which is available as shareware and a few test projects.

The book’s written on the premise of a very limited knowledge of electronics, computing or even how to use an oscilloscope, which is always a good place to start and at the bare minimum to follow this recipe would cost you a few quid to build a single channel probe. The below schematic shows how simple the circuit which sits between what you want to test and the soundcard is.


Now admittedly this principle comes with a caveat in that if you stick your probe on a voltage beyond the protection the circuit provides you’ll blow your sound card to pieces at the least and your PC at the worst! The book suggests nothing greater than 30 volts peak to peak should be attached to the probe.

That said, if you respect the limitations you get an oscilloscope for a few minutes labour plugging components into a breadboard or from whealding a soldering iron.

I decided to build the probe first and see what happened.


This thing had been sitting on my desk for several months waiting to be tested. Why? Well I can safely say I had a degree of scepticism about this project and really didn’t want to blow my recently rebuilt PC to pieces.

As a result my TOUGHBOOK was the designated crash test dummy for this one but even though it’s a cross between The Luggage from Terry Pratchett’s book The Colour of Magic and Arkwright’s cash till from Open All Hours (I’m sure its scheming how to bite my fingers off everytime I close the lid!) I really didn’t want to fry it.

One solution was to protect the PC by running the probe input into an external USB soundcard rather than the on board one. If that went up in smoke no great shakes. I had a Griffin iMic in the bottom of a box, never used and waiting to take one for the team.

So with the iMic attached to a USB port I gingerly plugged my probe in, sparked up Soundcard Oscilloscope and ran the test leads across my hand hoping to see a ripple on the trace. Absolutely jack on the trace. Great!

Now this could have been a problem with my build (doubtful as it was so simple), a level issue with the iMic (again doubtful as it had been duly tweaked) or the iMic doing something strange.

There was only one way to test this hypothesis and that meant giving the TOUGHBOOK both barrels, possibly.

So with every conceivable appendage crossed the probe was plugged directly into the on board sound card and bingo! It worked a treat. The trace below is the mains pickup from placing the probes against my hand.

Screenshot 2016-01-19 13.19.47

The next step is to package the probe board into a neat little enclosure to give it some mechanical protection.

Thankfully Mr Build Your Own Oscilloscope’s book even goes as far as showing you how to drill the enclosure so everything fits perfectly, if you buy the same enclosure as he did, which is a nice touch as trying to box things up to make a professional product can be a real pain.

Suitably armed with his working diagram I headed for the garage. Now the best thermometer I’ve got in the house is the cat and when the urban ninja is hugging the radiator and wearing a look of disdain at any suggestion of going outside you know it’s cold out there! Consulting something with a graduated scale rather than fur showed it was minus 3! I really do need to fit some form of heating in the garage.

Now after saying “isn’t it great to have someone show you where to drill the holes in the enclosure” I discovered a slight snafu in the book. There’s one crucial measurement missing from the diagram which prevents you from simply drilling holes and getting on with stuff. The annotated measurement in red should help anyone wanting to follow the book’s methodology.


Anyway, after an hour of numb fingers, warmed by several cups of coffee we have this.


The full specification of this oscilloscope is –

  • Useable bandwidth          20Hz-10kHz
  • Maximum bandwidth      20kHz
  • Maximum input voltage  30V Peak-Peak
  • Coupling                             AC
  • Channels                            1 or 2 depending on PC soundcard
  • Power requirements        Self-powered


And there we have one completed oscilloscope probe unit!

Step two is to build the calibration circuit and signal generator so the software can be calibrated to give meaningful data.

How to build an Atomic Clock

OK there’s a degree of licence in the title here, but unlike the “Daily Toilet Paper” which came up with headlines such as “Freddie Star Ate My Hamster” to increase it’s circulation, there’s more truth in my tag line than meets the eye.

You’re here now so read on!

As a kid I grew up in the era of having only three TV channels which switched off at midnight after the ceremonial playing of the National Anthem. As such there was a lot more radio in the house than there is today and I was always intrigued by “The Pips” which chimed out on Radio 4 at the top of the hour. I can see some people saying “You what?”

Yep those are “The Pips” also more formally known as the Greenwich Time Signal. As a nipper they always seemed a bit of fun just before the boring news, but when my Dad told me that they were generated by a very precise clock called an Atomic Clock . . . Wow! All sorts of mad scientist James Bond evil villain lair images sprung to mind. Now as you get older those images fade (slightly) as you become more educated and grown up, but the words atomic clock still conjure up images of machines the size of the CERN super collider. Now undoubtedly at one stage of their development they were and you could ask the question what use are they and what relevance is all this to radio as a sport?

Well firstly an atomic clock uses the “oscillation frequency” of particles (the rate at which they move up and down) to provide a very accurate time. That’s a bit simplistic but have a look at Wikipedia’s entry about Atomic Clocks for a more accurate explanation.

WSPR relies on a very accurate clock to sync the transmission and reception of WSPR signals.

Hence, accurate clock = a whole world of other radio related projects!

My WSPR receiver (see earlier posts) used a PC running Meinberg NTP to decode WSPR signals. My Ultimate 3 beacon uses a GPS signal to synchronise the clock within for transmission.

My plans next year are to have a crack at some other SDR projects based around new kit on the market and as part of the background reading ahead of parting with any money I discovered that one of these devices allowed for attachment of a 10Mhz external clock reference. A few months earlier, Everyday Practical Electronics (EPE) ran a constructional project around building, wait for it, an atomic clock or more accurately a rubidium standard. I can see peoples eyes glazing here but bear with me.

All a rubidium standard does, is provide a very accurate signal pulse, in the case of the EPE project it was a 10Mhz signal which could be used as a reference source for calibrating or testing things on a work bench.

I had visions of this costing thousands and requiring a degree in atomic physics to complete. Erm no, about £125 quid and the ability to solder half a dozen wires!


That my friends, is a rubidium standard. It’s about the size of a paperback book and thanks to our friends in China and the ex Soviet block there are loads of these things sloshing about on the internet. I’m sure they may well have been lurking in a bunker along with other things which would make you glow in the dark in less friendlier times, but in these days of world peace and consumerism they’re being flogged off left right and Chelsea! All you need to do is give it power and you’re off.

Now as tempting as it was to build one, I haven’t. What I have built is the next best thing, which is a precursor to other projects and is a proof of concept. It also has a host of practical applications.

What I’ve built is a GPSDO based NTP server. Again I here a “You what?” A GPS (Global Positioning System) Defined Oscillator based Network Time Protocol server.

Breaking it down further the GPS satellites orbiting the earth transmit a time signal which your satnav sat on the dashboard of your car receives, does some maths with the data inside that signal and works out where you are. That time signal is highly accurate, lets face it the US military have been using it to help bomb countries back to the stone age for decades so it must be good!

An NTP server provides computers with an accurate time reference. Have a look at Wikipedia for a proper introduction and explanation.

NTP helps keep things on track. Lets face it, without it your PC’s clock will drift significantly. If you have a rummage around in the clock settings within Windows you’ll see that Mr Gates wants your computer to use the good old Microsoft time servers by default.


Now that is all well and good and for the majority of people will do the job nicely, but like everything there are limitations.

NTP services are hierarchical in nature and the various levels are referred to as Stratum


Stratum 0 -These are high-precision timekeeping devices such as atomic (caesium or rubidium) clocks, GPS clocks or other radio clocks. They generate a very accurate pulse per second signal that triggers an interrupt and timestamp on a connected computer. Stratum 0 devices are also known as reference clocks.

Stratum 1 – These are computers whose system clocks are synchronized to within a few microseconds of their attached stratum 0 devices. Stratum 1 servers may peer with other stratum 1 servers for sanity checking and backup. They are also referred to as primary time servers

Stratum 2 – These are computers that are synchronized over a network to stratum 1 servers. Often a stratum 2 computer will query several stratum 1 servers. Stratum 2 computers may also peer with other stratum 2 computers to provide more stable and robust time for all devices in the peer group.

Stratum 3 – These are computers that are synchronized to stratum 2 servers. They employ exactly the same algorithms for peering and data sampling as stratum 2, and can themselves act as servers for stratum 4 computers, and so on.

Network speed, latency, network outage and so forth will reduce how “Average Joe” at the bottom of the pile receives their NTP source. By having a Stratum 1 computer within your network you are self reliant!

So, how many thousands of pounds does this cost I here you ask? Less than £50!

The ingredients for this little project are a Raspberry Pi (B+ in my case), a Raspberry Pi B+ GPS Expansion Board and an antenna.


Plumb it all together and you get


Apart from it looking pretty cool it does exactly what you want very well. The GPS Expansion Board is based on a Ublox MAX-M8Q positioning module and is pretty damn accurate! Admittedly it’s a motion based unit rather than a timing module but by issuing it with a serial command, it can be placed in “Stationary” dynamic mode which is the default mode for the much more expensive timing modules. I haven’t sussed that yet but all in good time!

The AVA High Altitude Balloon Project site has a very good How To which is what this project is based upon.

Also worth a read is the satsignal.eu Raspberry Pi Quickstart and the Raspberry Pi NTP guide.

Now unfortunately there’s a cautionary tale linked to this “How To”. All the bits turned up by Monday and on Tuesday I had a spare hour before going to work and decided to get it all working. The AVA walk through worked perfectly and I had the server generating a more and more stable time signal as it settled down after finalising things. Originally I had used a network cable to speed things up rather than using WiFi. The final step was to configure the on board WiFi to give it a fixed IP address and off you go.

Having played with Raspberry Pi’s before, the WiFi networking can be a real pain and not very stable but I bit on the bullet, started the GUI and began entering SSID’s and network passwords. At this point the GUI crashed quite spectacularly, locking up the machine. Having corrupted the SD card on a previous occasion by yanking the power cable I was reluctant to undo the last hours work, so while still being able to PuTTY into the Pi I rebooted it, only to find the damn thing had corrupted the SD card. Awesome!

Not wishing to be too defeatist, knowing it worked in principle I left it alone until Friday when I had a spare hour again to start from scratch. Until that hour turned into half a day! For some strange reason the device kept corrupting, refusing to boot and powering off the on board NIC so you couldn’t get into it via SSH or by being plugged into a monitor with a keyboard!

Now this caused a considerable amount of head scratching and effing and jeffing! Setting up a Raspberry Pi is simple but not the quickest of processes. At one stage I had two machines burning Wheezy and Jessie images to SD cards in a little production line ready for when I trashed the next one!

Both the AVA guide and Satsignal.eu guide have the following primary steps which get the Raspberry Pi ready for installation of the packages which actually do the clever stuff –

sudo raspi-config
1. Expand Filesystem
2. Advanced Options -> Disable Serial Shell (optional)

sudo apt-get update            – tells the Pi to update its list of available packages
sudo apt-get dist-upgrade – updates the Pi’s distribution to the latest version
sudo rpi-update                    – updates the Pi’s firmware to the latest version
sudo reboot                            – reboots the Pi ready for the next stage and allows the updates to finalise and so forth

sudo apt-get install pps-tools – first step of installing all the necessary bits and pieces to get the GPS side of things working

Now by process of elimination (and this wasn’t quick!) I found the Pi was dying after pps-tools was installed, which was far from helpful.

The only conclusion I could make is that between Tuesday lunchtime and Friday morning a package in the distribution upgrade or the firmware update had been altered/upgraded and released to the world, which was killing the Pi once pps-tools was installed.

Proof of concept comes in that if you omit the steps

sudo apt-get update
sudo apt-get dist-upgrade
sudo rpi-update
sudo reboot

everything works perfectly!

Now how do you prove it’s working? Good question. Once the NTP server is running, issuing an ntpq -p command gives you data

Screenshot 2015-12-20 16.42.04

  • The display is a list of remote servers with various status reports arranged in columns.
  • One remote server should have an asterisk (*) in the first column.  This marks the server which NTP has selected as the current preferred source.
  • Servers which have a plus sign (+) are good enough for NTP to sync to, others are not.
  • The reach column should not be 0, and will expand from 1 during the normal working of NTP until it reaches 377.  It is an octal display of a bit-mask showing when the server was reached.  Normally you expect to see 377 in this column against each server.  A column of all zeros means that NTP can’t contact any servers.
  • The offset shows how far your PC is off from a nominal UTC, and the value is in milliseconds.
  • The poll value should gradually increase from 64 seconds to 1024 seconds as NTP needs to contact the server less and less frequently as the clock offset and frequency are gradually corrected.  Changing the poll is automatic in NTP.
  • The delay shows the time for a packet from your PC to reach the remote server and vice versa.  Values above 150ms may indicate a satellite circuit and it’s best to avoid such servers if possible.  You will get best performance from servers which are close to you on the network.
  • The jitter column shows how stable the connection between you and the remote server is.
  • The st column shows the stratum of the server, with stratum 1 servers having a local reference such as an atomic clock or, for many servers, a radio-clock or GPS receiver reference.  Most servers you will see are at stratum 2, so they are locked to a stratum-1 server.  A lightly loaded stratum-2 server is probably a better reference than a heavily loaded stratum-1 server such as those with widely-publicised addresses.

Now that the server is working and providing good stable timings it’d be a shame not to share it! This can be done in a multitude of ways. You can add the IP address of your NTP server to you hosts file within Windows as a TIMESERVER, so when you go to your time and date settings it’s there as an option to select.

Alternatively, if you use Meinberg NTP, by adding the NTP server to the ntp.conf file your local machine then has a Stratum 1 time server available to it.

Screenshot 2015-12-20 16.46.56

I’m slowly editing all the clock settings on my network machines to allow them to utilise the local NTP server as well as trying to get my head around trying to monitor the server’s stats using MRTG. MRTG is easier said than done as it’s based on Pearl and I haven’t done any scripting in years, but that’s another rainy day project.

As I said at the beginning this is a proof of concept for another project and it works a treat!


Raspberry Pi RTL-SDR Frequency Scanner

Being one to never miss a bargain I grabbed a handful of Raspberry Pi Model B’s off of eBay a while back for an absolute steal when the new model was released. Since then I’ve been trying to put them to good use. The Tiny Python Panadapter was one project. The other is a RTL-SDR Frequency Scanner inspired by the Adafruit project Freq Show: Raspberry Pi RTL-SDR Scanner – See what’s in the radio waves around you using software-defined radio and a Raspberry”



Now to get this thing working you need to add a 3.5″ TFT LCD display to the Raspberry Pi. It’s a nice ergonomic screen which fits perfectly over the mainboard and is nice and stable preventing it from being bent or snagged.

The Adafruit project uses a PiTFT screen which is nice, expensive and has been out of stock for quite a while. Now, foolishly to a degree, surfing eBay for alternatives may seem like a good idea but be warned. There are some very nice 3.5″ screens out there for an absolute snip but as to what you actually get when the dice are rolled is another matter!

My £13 landed a Waveshare Spotpear 3.5



This screen came with a driver disc which supposedly has a pre-configured disc image which supports the screen out of the box, simply needing to be burnt to an SD card. The Pi boots, screen works and everyone is happy. Until the image on the disc has a corrupted file! If it helps anyone in a similar situation, when extracting the .img file an error is reported by 7-Zip stating that a single file within the archive is corrupt. As to which one, take your pick it could be anything (harmless or harmful).

Now I must stress that this screen didn’t come directly from Waveshare, which is probably why the disc is more use as a drinks mat than anything else. The fact the vendor has disappeared into the ether when I’ve emailed and asked for a replacement or directions to a genuine disc image did make me wonder if I’d been well and truly seen off!

So, with fingers crossed that it was a simple help file that was broken rather than anything more vital, I blundered on and burnt the image to the SD card and booted up, or at least tried to. The boot process hung with all sorts of errors namely to do with not being able to mount the root partition. Nothing I tried overcame this problem.

My money was now definitely on the “been seen off” side of the Roulette table!

Now a lot of time went into Google research in an attempt to overcome the “out of the box” solution, only to find a whole community of people who were regretting the day they bought a Waveshare Spotpear 3.5!

I resigned myself to having to build a custom kernel based around the advice of various forums out there, but again and again people were reporting lack of support for this specific device, which is never a good sign. That said in the middle of a huge forum post I found this link


Someone had posted this as a working solution for the Waveshare Spotpear 3.5

It is thankfully, a boot image which actually works. Once burnt to an SD card, the Pi boots, the screen springs to life and all is good.

As proof that this thing is real and does actually do what it’s supposed to do, here’s a snap of it in action.


The support documentation with this image is actually very good and helps with calibration and use with other peripherals such as cameras. All I need to do is calibrate the screen and the touchscreen functionality and we’re in business.

As an aside, to prevent the image becoming unusable after performing any system update make sure you do the following –

sudo apt-mark hold raspberrypi-bootloader
sudo apt-get update
sudo apt-get upgrade

The Adafruit article requires the screen side of the project to be running correctly before the RTL-SDR elements are installed, so watch this space.

24 hours on and I was able to get this project finished. With the screen calibrated and working perfectly it was a simple case of following the Adafruit project through and then starting the python script. There was a degree of apprehension when the screen went blank, but a few seconds later it sprang into life!



After tweaking a few settings we were in business. The trace shows The Chris Evans Breakfast Show on Radio 2.





To tidy things up I salvaged yet another piece of metal from the D-Link switch case which I used to make my dummy load and fashioned an angled viewing bracket for the Pi. A light blast through with a spray can and a few rubber feet finished it off nicely. The Pi has two holes in the PCB and with a few brass spacers and some screws everything was bolted together.


It gives it a nice angle of tilt to make the screen readable plus keeps it still. The temporary prop made from a block of notelets wasn’t cutting the mustard and it was sliding all over the shop, plus it keeps the back of the main PCB away from any harm!

MFJ-971 portable ATU modification

Unlike the posts of the past few days, which have been sat as drafts for several weeks and I’ve just tidied up and pressed send, today’s offering is hot off the press.

Several months ago the guru suggested investing in a portable ATU capable of QRP work, specifically the MFJ-971.


After waiting patiently for a few weeks, one popped up on eBay and I managed to get it for less than 50% of a new one, so happy days.

Then he hit me with the “you’ll need to mod it” line. What? Why? How?

No worries, a very kind sole, also playing in the “share the knowledge game” had been there before and had posted all that needed to be known here.

For my work, all I need at the moment is the bypass switch.

So today, faced with the prospect of more episodes of The Blacklist (which is very good watching) I made the conscious effort to be both practical and creative and donned multiple layers and ventured out into the garage.

I’m not saying anything, but there’s more chance of seeing Monty and Mabel in our garden today than in a John Lewis store! It’s freezing.

Now, when this thing arrived it had obviously been loved and looked after by it’s previous owner. It arrived in it’s original packaging which is huge, wrapped in a protective film. And now I was about to set to work on it? It didn’t seem right.

When I sprung the case, the whole thing smelt of a solidly built item designed by people who care about all things radio and want it to last. It could probably withstand a nuclear war!

The fact the manual consists of 3 pages of letter sized paper typed on a typewriter in Courier font, single line spaced with no diagrams shows these are the kind of people who will shoot you without hesitation for blaspheming at anything radio related.

Forwards and onwards! My biggest worry was drilling the case as it’s a nice unit and a drill slip would have pained me for ever and a day. Thankfully that went without a hitch and the DPDT switch was installed.



With the unit in front of me, the blog notes from M0UKD made a lot more sense.  The one thing I was warned of, was the need for the biggest soldering iron tip available. Advice well worth every penny as the wires in this thing just suck the heat up. I tried to desolder the antenna capacitor and transmitter capacitor leads but gave up and gently trimmed them in the end. It’s worth cleaning up the attachment points as the flux or resin from the manufacturing process didn’t give the easiest surface to work with.

I soldered four 3″ fly leads to my switch and soldiered on. In about 15 minutes, all done. A quick whip round with the DVM to make sure everything was where it should be and we were finished.



And now, with the case back on its ready for action. As others have commented, it’s a shame the bypass switch isn’t there as a factory fit, but like most things in life, you can’t have everything.

Besides, there’s fun to be had taking things apart and making them do things they were’t designed to do!