Category Archives: Kits

An Introduction to the uSDX transceiver kit

Many thanks to Pete (WB9FLW) who shares the following article by Bob (KD8CGH) regarding the uSDX transceiver kit.

I reached out to Bob who has kindly given me permission to share his article on QRPer:

An Introduction to the uSDX

by Bob Benedict (KD8CGH)

There is a new open source, home brew multi band, multi mode QRP transceiver that grew out of the QRP Labs QCX. Through some serious wizardry  it retains an efficient class E RF amplifier for SSB and digital modes. It crams impressive SDR capabilities into an Arduino.

This has an interesting international development process conducted on with contributions by many, including the usual gang of suspects: Hans Summers G0UPL, Guido Ten Dolle PE1NN, Barbaros Asuroglu WB2CBA , Manuel Klaerig DL2MAN, Kees Talen K5BCQ, Allison Parent KB1GMX, Jean-Marie T’Jaeckx ON7EN, Ashhar Farhan VU2ESE,  and Miguel Angelo Bartie PY2OHH. I apologize to the many others whose names I didn’t list. A summary is in the WIKI

The basic work uSDX appears to have been accomplished by Guido Ten Dolle PE1NNZ. It uses pulse width modulation of the PA supply voltage to transmit  modes other than CW while retaining class E efficiency and uses a direct conversion SDR receiver.

The basic idea behind Class E nonlinear amplifiers is that transistors have little loss when they are switched fully on or off. The losses occur when devices are limiting power flow in linear amplifiers. The idea behind a Class E amplifier is to use transistors in a switching mode to generate a square wave to drive a resonant circuit to generate RF power.

This method is used in the popular QCX QRP CW transceiver kit line developed by Hans Summers and sold through QRP Labs  More than 10,000 of these great transceiver kits have been sold (I built one). There is a good discussion of the circuit and particularly of the class E amplifier in the excellent QCX documentation

The QCX was the base for the QCX-SSB which starts with a QCX and modified the circuit and software to add SSB capabilities. The wizardry that  Guido accomplished uses pulse width modulation of the PA supply voltage to control the amplifier in an Envelope Elimination and Restoration (EER) technique To generate SSB a DSP algorithm samples the  audio input and performs a Hilbert transformation to determine the phase and amplitude of the complex signal.  The phase changes are transformed into temporary frequency changes which are sent  to the  clock generator. This result in phase changes on the SSB carrier signal and delivers a SSB-signal with the opposite side-band components is attenuated.

On the receive side a direct conversion SDR receiver is used with the I and Q signal digitized and all further processing carrying out digitally. Attenuators are included to help not overload the ADC range.  Documentation is at .  In addition to a good description of the theory and hardware mod there is also a good description of the software command menu.

From there development took off in several directions. One is by Barbaros Asuroglu WB2CBA  and Antrak that uses through hole components (mostly) and replaceable band boards that  hold the low pass filter and band dependent class E amplifier components (an inductor and capacitor). Barb also includes boards designed to be a case top and bottom, battery pack and a PA.

Another development track by Manuel Klaerig DL2MAN uses SMT components in a stacked board layout and has a relay switched band pass board  and uSDX-Sandwich Files. A new revision has been released that uses serial resonance class E amp design and easier to obtain relays, uSDX-Sandwich Files with new Serial Resonance Class E Multiband Circuit .

Other development streams include one by Kees Talen K5BCQ uSDX Board Schematics and Jean-Marie T’Jaeckx ON7EN

I built the variant designed by Barbaros Asuroglu WB2CBA   and I’m pleased with it’s performance. I ordered 10 main boards and 40 LP filter band boards PCBs from PCBWAY, but now you can also purchase single boards sets from

I also designed and 3D printed a case for the transceiver and a small box to carry band boards. Info at and at and also in the files section printed case for Barb WB2CBA V1.02.

In an example of hams collaborating at its finest, Hans Summers  announced on 9/11/2020 that his new QCX mini product, a QCX in a smaller package,  will include a daughter board that can be used to give the QCX mini a uSDX like SSB capability. The QCX mini has the same circuit as the QCX but uses SMD components packaged it into a two board stack that is less than half the volume of the original QCX. The mod is unsupported by QRP-LABS but may be supported by the uSDX group. 

More information at and don’t forget the WIKI


Bob,  KD8CGH

Many thanks again, Bob, for sharing this excellent uSDX introduction. Thanks again for the tip, Pete!

Pete also notes that there is a very active uSDX experimenters discussion group on with over 100 members:

The new Inkits Easy Bitx SSB TCVR kit

Many thanks to Robert Gulley (K4PKM) who shares the following news from Inkits:

This is to inform all our valued subscribers that we have launched the much awaited easy bitx kit and few customers have already bought the kit.

The easy bitx kit works on a single band and can be built
for 20mt 40mt or 80mt bands.

This is an enhanced bitx design from the previous versions.
There is a complete manual available with link below.

Easy Bitx Version 1

Complete details are provided in the construction manual to build the kit in 15 Steps.

There are 15 individual kits packets provided to assemble the kit step by step.

The si5351 BFO VFO is provided with the kit in working condition. Only The IF frequency has to be set as described in the manual.

The easy bitx kit is an excellent educational kit for new Hams
who are wish to learn how to build a single band transceiver.
And later use it on the air.

The bitx in various kits and individual mods has been build by thousands of hams world wide, so this way easy bitx is a perfect kit for newbies.

The complete kit can be purchased from our website.

Presently we are shipping world wide with DHL Express.

Adding CW mode to the EA3GCY DB4020 Dual-band 40 and 20M QRP Transceiver Kit (Part 2)

Many thanks to SWLing Post contributor, Frank (ON6UU), who shares the following guest post which expands upon his previous DB4020 article:

The EA3GCY DB4020 transceiver now has CW mode

by Frank Lagaet (ON6UU)

After telling you all about the DB4020 SSB build I’m here with the CW part of the kit,  let’s say this is part 2.  At a certain moment Javier let me know the CW interface kit was ready for shipment and some week later it was delivered to my QTH.

Again, a well packed kit arrived in a brown envelope, components and boards well packed in bubblewrap.  I found even a board I did not expect which can hold a push button,  a switch and the connector for your morse key.  Javier thinks of everything it seems!

Unpacking the bubblewrap gave me this result,  all components in 2 bags.  In the bigger bag another 2 bags with 2 printboards,  one for the CW interface,  one for the CW filter.  Great !!  Checking the material bill resulted in all components there,  another thumbs up.

I started, of course, immediately building it because I wanted CW in the transceiver as soon as possible.  I don’t do much in SSB mode anymore and I already started missing CW on the DB4020,  so I started my KX3 to listen to while I was populating the boards.  I never thought CW was going to have this impact on me! …. ..

I started building the CW interface,  again starting with all small items.  I soon saw that the 2 relays which need to be soldered in were ideal to protect all components when the board is upside down, so I soldered them in very quickly.  I then soldered in all other components ending with the elco’s.

Next phase was the CW filter.  This board is small and came together in a blink of an eye, no problems there, the long legs of the 3 and 4 pin headers went in last.

The following day, I made all wire connections and soldered a 13pin connector,  leaving one pin out since I want to have the option to choose the width of the CW signal I’m listening to.  By cutting the FL CW + pin and adding an additional switch, I have now 500Hz or 2400Hz.  Great option, for very little effort and simple.  Another thumbs up here.

Now it was simply a matter of inserting the sub boards in the main board and all should be working.  And it did!  Hurray!  The 500Hz filter works perfectly,  filtering away all above or below stations nearby my operating frequency.

This is the result of the soldering work,  2 small boards which need to be inserted in the main board:

The CW interface still needs the 13pin header of which I cut one pin and mounted a switch to have the 2400Hz width.

The IC you see in the middle of the CW interface is the KB2 keyer which gives you several functions like 4 memories and beacon mode.  The 4 potmeters are used to set the level on 40 and 20 meters,  to set the delay between TX and RX switchover and to set side tone monitor level.   The keyer also provides functions as keyer mode A or B,  straight key function and can be set for speeds between 1 and 50WPM.   WPM speed can be set in 2 different ways.  Handy!

Here a picture of the CW filter inserted on the main DB4020 board.

The CW interface is inserted at the side of the main board,  notice the 2 wires which go to the switch to allow switch-over between 500 and 2400Hz.

(Wiring still needs to be cleaned up in this picture.)

Finally, the result:  a good working multimode QRP transceiver with 2 bands.  It should be possible to make close to medium range with it as well as DX,  even with QRP power.

And while I was building I also made a new key for this radio,  it is made out of a relay and cost nearly nothing,  looks good doesn’t it ?  hihi.

Homebrew key

The key, when in practiced hands (fingers hi), can do 50 WPM without a problem. My friend HA3HK does without blinking an eye at 40WPM with this kind of key and tells me that he can go faster if needed.  Me? I’m going it a bit slower.

Battery pack

As this radio is only using little power (0.4A in RX,  1 to 2A in TX depending the power you set it) I thought,  let’s make a battery pack for the radio.

The first plan was installing it in the box.  I did not do that because the batterypack is also powerful enough to feed my KX2 and other QRP transceivers. Since I can use it with all of them, a loose battery works out better for me.

I started with an old laptop which had a broken screen and some other malfunctions,  but still had a good battery,  although I needed the battery connector of course.  A piece of wood to mount the connector on was my next goal.  And since I still have another laptop using the same batteries, I can charge the battery without problems.  Simple, but good and it weighs much less than a gel cell battery.

The battery provides me with 12.5V and some 5Ah.  Enough to last for hours on RX and for sure good enough to activate 2 SOTA sites in one day.   It doesn’t look great but works great– that is what matters and to test it was more then good.  Next will be getting the battery pack in a nice box.  Better to re-use stuff than throwing it away I’m thinking.

I need to do something about the cover of the OLED display,  there is still some work there to make it look nicer.

Some video can be seen on YouTube :

Finallym I’d like to thank you all for reading my articles about the DB4020. I had big fun soldering, tinkering with the box, making the key, and batteryholder/batterypack.  My Hungarian friend HA3HK told me it looks a bit like a spy radio. …. ..

I also include one more time the link where you’ll find this kit :

73 TU ee



Thank you so much, Frank. No doubt, you had a lot of fun putting this excellent little kit together.

Implementing a filter switch was a fantastic idea and, obviously, not terribly difficult to do.

Based on the videos, the DB4020 has a low noise floor and very good receiver characteristics. I’m impressed that the CW portion of the radios has so many features as well, such as a memory keyer and beacon mode.

I also love how you reused that 5Ah laptop battery! I think that could almost give you a full day of SOTA activations at those consumption levels!

Thanks again for sharing this with us, Frank! We look forward to your future articles!

Frank builds the EA3GCY DB4020 Dual-band 40 and 20M QRP SSB Transceiver Kit

The following article first appeared on our sister site, the SWLing Post:

Many thanks to SWLing Post contributor, Frank (ON6UU), who shares the following guest post:

Building EA3GCY’s DB4020 QRP Transceiver kit

by Frank Lagaet (ON6UU)

In May, I discovered via a newsletter that a new kit was available from Javier EA3GCY in Spain.  I was immediately sold as this was a kit from my favourite kit producer and it has 2 bands–it will also be able to do CW and there also will be a CW filter.

After building 2 MFT’s from Javier which work without problems, I needed to have the DB4020.  The MFT’s are for 20 and 40 mtrs and do DSB (double side band).  I did put them in a not-so-graceful box but they do what they are intended for which is QRP phone (SSB).   They came together without problems so I expected the same for the DB4020–I knew for sure when I saw the board:  all through-hole components (except for some capacitors which are factory soldered) and a lot of space on the board.   The board has been silk-screened with clear indications on where all components have to come and the manual has very clear instructions where each component has to be soldered with referral to a quadrant.  The manual provides a 252 quadrant page so it is a piece of cake to find where each piece goes.

What do you get?

Javier provides you with all components which need to be installed on the board and, of course, the kit board.  The components come in small marked plastic bags and all is well-wrapped up in bubble wrap.  The board is wrapped separately and that is put together with the component wrap which is then again wrapped up in bubble plastic.  All goes into an envelope.  Very well packed I must say.

Here’s a picture of the bags with components:

The silk-screened board:

I started with the resistors since that’s the easiest way. After that, I did the capacitors.  I like to solder in all flat components first, so next were the diodes and IC sockets followed by the elco’s.  The transistors were next together with all relays.  As you solder in the transistors one also has to mount the cooling heatsinks,  these cooling sinks are high and are ideal to protect the coils one has to make,  they also protect the polystyrene caps (which I always find vulnerable) when the board is upside down.

Many kit builders are afraid of winding the toroids in kits–don’t be!  It is easy.  Just take your time and follow the instructions given by Javier in the construction manual.  In this kit the builder has to wind 8 toroids:  6 are a single wire which goes through the toroid body,  1 is a toroid with 2 different windings, and 1 has a twisted pair which goes through the final toroid.  Be sure to measure the wire you need per toroid as instructed in the manual.  Javier gives some spare, so you can be sure.  You will also see that on next picture where the legs of the toroids have not been trimmed yet.  Once done I still had some centimetres of wire leftover.

Picture of the toroids ready to be soldered in:

Finally all other parts and pin headers went in,  jumpers were immediately put on where needed.

As I’m using a military-grade plastic box, I have to break-out some components like the display,  tuning encoder,  volume and rx control from the board.  I also have put an on/off switch on the box and already have the CW KEY connector ready installed. I also installed a loudspeaker in the box.  The SI5351 board and the Ardiuno Nano are the final components which go into the board after installing all wires.

Picture of the board:

I intend to attach a CW paddle to the box made out of a relay.  A HWEF tuner (from EA3GCY) which I was planning to incorporate in the box is I think a bit overkill. That HWEF tuner is already in a nice little box and would be a pity to dismantle,  also I’m running out of space in the box…  Maybe I can fit in a 9-1unun which would then give me good results on both bands…?

Maybe I will install a battery pack in the same box.

The box with board installed:

The box completed front side:

Mind you,  it still needs some additional switches for the CW part of the transceiver.

Frank (ON6UU)


Brilliant, Frank! I really appreciate the video as well–sounds like the kit produces smooth audio and should serve you well. No doubt, that military box enclosure will survive even the roughest field conditions!

Click here to check out the DB4020 kit at EA3GCY’s store.

QRP Labs new QCX+ QRP CW/WSPR transceiver kit

Many thanks to Pete (WB9FLW) who writes:

Hi Thomas,

QRP Labs has just announced the QCX+ which as the name implies is an upgraded version of the very popular QCX line of transceivers

To date almost 10,000 kits have been sold, here’s a brief overview of the the differences and new features made to this popular Transceiver.

The QCX+ is the almost same circuit as the QCX, with two very minor changes. QCX+ runs the same firmware as QCX, and has identical operational and performance characteristics. QCX/QCX+ firmware will always be compatible with both the QCX and QCX+. The evolution of QCX to QCX+ provides several improved features in physical layout, as follows:

1) Physical layout of controls and connectors

2) Optional enclosure

3) Additional and changed connectors

4) More spacious PCB, more than double the board area, with less densely packed components, and more test/modification points

5) Improved heatsinking

6) Three minor circuit changes

7) No microswitch key

Price has gone up slightly to $55, still no other QRP Transceiver on the market today comes close to the features offered by the QCX+ at this price point.

More Info:

Thank you so much Pete! You’re an enabler! Since I’m not at Hamvention right now, those radio bucks are burning a hole in my pocket. The QCX+ looks like a fun transceiver to build! Thanks for the tip.

The uBITX V6 is a power outage companion

QRPer Readers: Please note that the following is a cross-post from my other radio blog, the SWLing Post. For more information about the uBITX V6 and a short post about assembling it, check out this post.

Yesterday, a weather front moved through the area that dropped temperatures from an unseasonably high of 50F to 25F in the space of a couple of hours.  Fronts like this always equate to high winds here at our altitude. This time, it packed a little snow as well.

Last night, around 22:00 local, our power went out due to a fallen tree further down the road.

Here at SWLing Post HQ, we don’t panic about power outages. As I’ve mentioned before, our refrigerator, freezer and some of our home lighting is solar-powered and off-grid–we also rely on passive solar heating and a good wood stove to keep us warm and cozy.

Without fail, I always use power outages as an excuse to play radio on battery power.

This morning, the uBITX V6 transceiver was already hooked up to a LiFePo battery on my desktop, so I simply turned it on and started tuning around the 40 meter band, where I had recently logged a few POTA contacts. Problem was, the band was absolutely dead, save a couple weak stations. After thinking about it a few seconds (keep in mind this was pre-coffee) I put on my boots and coat, walked outside and confirmed my suspicions: the antenna feedline had become detached from my external ATU box.

The winds were strong enough last night, that the ladder line pulled itself out of the banana connector jacks on the side of the ATU box. This happens quite often during periods of high winds and is a bit annoying. Of course, I could secure the feedline in such a way that it would easily survive high winds without disconnecting, but frankly this is an intentional design choice. You see, when a black bear walks into my feedline, it easily disconnects before the bear gets tangled, up, frustrated and yanks my antenna out of the tree!

Trust me on this: bears and antennas don’t mix. I speak from experience.

After re-connecting the antenna, I fired up my portable alcohol stove (the one you might have seen in this post), boiled water, and made a fresh cup of coffee to take back to the shack.

I turned on the uBITX once again and found that the 40 meter band was chock-full of strong signals.

It’s time to go chase a few more parks today and plot my next POTA activation.

Frankly, I’m in no hurry for the power to be restored.  It’s a wonderful excuse to play radio.

Readers: Anyone else enjoy radio time when the grid goes down? Please comment!

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uBITX v6 QRP transceiver now available for $150/$199 US

Many thanks to QRPer, Pete (WB9FLW), who notes that Ashhar Farhan (VU2ESE) has recently announced the availability of the uBITX v 6.0–as Pete notes, “just in time for the Holidays!

Pete shared the following message from Farhan:

Here is what [the uBITx v 6.0] looks like :

And of course, you can buy it on The shipping will happen from Tuesday onwards. We have a limited supply of the first 200 boards. The rest is for after Christmas.

The most important thing about this revision is that the Radio circuitry is almost unchanged. We have incorporated the connectors on the PCBs. So, this kit needs none of the confusing soldering. You snap in the TFT Raduino onto the main board, plug the power and antenna from the back, snap on headphones, plug in the mic (supplied with the kit) and off you go!

It is offered in two kits now : The basic kit (150 USD) is without the box (like old times) but with a microphone and two acrylic templates for the front and back panels.

The Full kit (199 USD) has the box with speaker, mounting hardware etc. Both are described on the website.

Now, about the TFT display:

For those who are using the 16×2 display and you would like to upgrade, you will have to do three things:

Add a heatsink to the 7805 of the raduino

Buy [here] and hook it up as per [this article].

Grab the new Arduino sketch from


I have been hacking away at adding a TFT display for the Arduino for sometime. Finally, I managed to do this with a really inexpensive 2.8 inch TFT display that uses a controller called the ILI9341. The display update is slow but, clever guy that I am, the display very usable. it uses the same pins that earlier connected to the 16×2 LCD display. This display is available everywhere for a few dollars.

Many thanks, Pete, for sharing this announcement. The price was simply too attractive to me, so I just purchased the full kit for $199 US. (Thanks for being the good enabler you are, Pete!)

I’ll post an update when I receive the transceiver and assemble it. I do hope this is a workable little radio–it would be pretty amazing for newcomers to the hobby to be able to get on the HF bands for a mere $200 US. I also love the fact that this is all based on open-source, hackable technologies.

Dave Benson’s new Phaser Digital Mode Transceiver kit

Many thanks to QRPer, Pete (WB9FLW), who writes:

Just in time for Christmas, Dave Benson is back with a great new line of Monoband Digital Mode Transceivers! 40 & 80 Meters is available now 30 & 20 Meter Rigs to follow shortly.

Time for me to contact Santa Claus and update my Christmas Wish List 🙂

These are Single Signal Phasing Rigs not DSB.

Pete WB9FLW,

WOW! Thanks for the tip, Pete! I think I might give Santa a hint! This looks like a fun kit!

QRPGuys new DSB Digital Transceiver kit

Many thanks to QRPer, Pete (WB9FLW), who writes:

QRPGuys has just introduced a new Multiband DSB Digital Transceiver for FT8.

At $40 it introduces a new price point for such Rigs as it includes band modules for 40/30/20 Meters! For those wanting to experiment with different Bands extra bare boards are available for sale.

The rig as it comes is crystal controlled for FT8 but fear not the main board includes connections for an external VFO. As an example one could use one of the very popular Si5351 VFO Kits and be able to QSY to operate the different modes available to the Amateur Community today.

Let the fun begin 🙂


Thanks so much for the tip, Pete! What a great little project!

Click here to check out the DSB Digital Transceiver at QRPguys.