This page is work in progress and may be updated frequently (last update : 2023-08-20 12:23 UTC). 

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Loving the kits from QRP-Labs, and when Hans Summer announced his new QDX digital signal tranceiver I knew I wanted to buy and build one. And when he added it to his webshop I didn't hesitated for a moment  and was to late. The next batch, I forgot, but when the 3rd batch was sold I didn't and I ordered a QDX incl the housing.  

This little kit with a stock of 1000 was sold out in under 4 days. Showing that hamradio kitbuilding is here to stay.  
So after a litte more then a week the parcel service dropped of a package from QRP-Labs. 

Content :


FYI : I sorted the components and put them in the plastic storage box (it's not how QRP-Labs ships there parts).

I got a revision 3 PCB. All SMD components are installed 

Front side 


Back side. 



The manual

As with every kit which Hans sells, the also was a very nice manual for the QDX - Digital Transceiver (link).  Chapter 1 contain a Introduction  Chapter 2 contains a list building general guidelines, images of the PCB layouts (track and component placement),  technical specification and the full Parts list of all components in the kit and photo's of a finished QDX allowing to kit builder get a idea about what to expect. And after sub chapter 2.3 Inventory parts helping the starting kit builder to identify parts, the fun starts.

Let start building 

Because my eyes are getting worse, I used  a magnifier to sort the capacitors and write the value on the paper tape.  That way I don't have to continuously use the magnifier.  


Section 2.4 describes the placement of the capacitors and after a 15 minutes of soldering all the capacitors where in place.  


 Section 2.5 describes the placement of the 6 diodes and section 2.6 describes the placement of the 4  47uH inductors


 Section 2.7 describes the placement and installation of the 4 BS170 fet's. 


 As of section 2.8 the fun really starts. I don't know why, but a lot of OM's hate winding toroids, coils etc. For me it's a very relaxing thing to work on.

Hans writes in his manual : 

It is a good idea to de-burr the toroid because sharp edges can damage the insulating enamel on
the wire – however be careful since the ferrite is brittle and can easily be broken. So GENTLE
scraping of the edges with something sharp like a knife is possible.

I took a closer look at the BN43-202 binocular ferrite and indeed there were a few sharp edges. To remove them I use my old scraping tool which I own for decades. 


 I used have to place the tip of the tool into the BN43-202 binocular ferrite and turn it a few times and all the sharp edges where gone. 


And following the instructions in Section 2.8 I wound the BN43-202 binocular ferrit.


 I remove the enamel off the wire I use a X-tal knife and a stainless steel plate (see also this how-to).


By just turning the BN43-202 binocular ferrite 4 times, all enemal is scraped off and 


 Hmmm looks like a kind of animal. 


 The BN43-202 binocular ferrite is installed.


 For some reason I skipped winding the other toroids and started with installing the connectors as described in section 2.14. To be sure the connectors are in the correct place, I used the back plate from the optional enclosure.


to keep the DC chassis part in place and aligned I plugged in a DC plug to keep it in place.  


A day later I started again in section 2.9 and took time to wind all the toroids (but forgot one).
Quiz question : which one did I forget ? 


After removing the enemal from the wire with X-tal knife and a stainless steel plate (see also this how-to) I soldered the toroids in place. 


Answer, I forgot the trifilar toroid T2 as mentioned in section 2.12. But no worries, I found out before applying power ;-) 


T2 installed so we are almost done. 


 The status LED is soldered in place and the tape as mentioned in section 2.15 is also installed. 


Time to box it all up acording section 2.15 Optional enclosure.


Powering it up : smoke test

Then the big moment was there. USB cable connected, Antenna connected, 9V power applied, current draw 140  and  . . . no magic smoke.

That's a good starting point. 


 Because I build the QDX for a 9V supply voltage I added a label on top of it, that I should be powered with 9V only. 


 I followed to operation manual  (link) and used a terminal program to look around in the configuration menu see Section 4.

Does it work ? 

After everything looked good, I configured a instance of WSJTX as described in section 2 of the   operation manual  (link) and after a while RX on variouse bands, I decided it was time to try to TX and I called MQ3FON. MQ3FON replied and gave me a report. So TX also seems to work.  


Monday 20 june 2022, I was a day off and left the QDX on to monitor FT8 on 20m. Below are images from a 6 hour RX / TX report from PSKReporter
(click on image to get more detailed image)



Note : Once in a whille I replied to a CQ (interrupts from working in the garden).

Conclusion : yes my QDX works. And with a RX current of about 140 mA, I can leave it on cheaper then my FT897D for monitoring WSPR / FT8.

Output power and current draws

To measure the output power, I the use of my Rigol DS1054 scope with the following settings : 

  • Coupling : AC
  • BWLimit : OFF

For every band I used the FT8 frequency and clicked Tune in WSJTX, wrote down the UMax (V) value and used the following formula to calculate P output (W)


Also I wrote down the RX and TX current (at 9V).


IMHO it doesn't need much tweaking (for now).

Latex code for formula (I used https://www.codecogs.com/eqnedit.php as a editor ) : 


9V? Yes 9V

I have made my QDX to be operated at 9V (6 x 1.5V AA battery compatible) and because my main DC in the shack is 13.8V with powerpoles I needed a little step down box.

For that I used a  L78S09CV from STM which is a fixed linear voltage regulator capable of handling 2A. The schematic is very straight forward as shown below.


The PCB was cut to the size of the  small die cast aluminium case and used my Proxxon Micromot to cut the tracks and for the PowerPole connector I used the PA4Q powerpole chassis part.




2 stickers made with a labelwriter finishes it. 


Does it get warm ? Well a little (3.84W) but the metal box is dissipating enough

The QDX can be used for long duty cycles although not recommended (unless you reduce power). The peak currents are described in the QDX manual page 72 (max 1.1A).

To reduce output power I have plans to build another box like this which output's 6V. That one will need some kind of heat sink  because it will generate aprx 6.25W in the peaks. 

What's next ? 


Setup a Raspberry PI to make a permanent WSPR monitor (using my PA0RDT mini-whip antenna as the RX antenna).



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