QCX+ CW radio kit from QRP Labs

QCX+ CW radio kit from QRP Labs
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Hello friends! Not a SOTA activation report this time. I took a break and spent some time with a soldering iron in my hands!

SOTA is not only about hikes and operating radios but also about building your rigs and antennas. When a heap of dead and cold components turns into a radio one can use to make contact with people hundreds miles away it is pure magic. This never gets old. So I couldn’t be happier when Hans G0UPL announced he’s updating his excellent QCX transceiver kit.

I’ve immediately pre-ordered the upgraded version.

QCX was good but…

About a year ago I got my first QCX kit. I just got my Technician license and was looking for some easy-to-medium difficulty kit to get a refresher on soldering. Also I was thinking about a simple CW rig for SOTA. Ordered 20 meter version.

I’ve built the kit and had a lot of fun in the process but eventually QSX didn’t quite work out as a SOTA rig for me. I couldn’t read Morse code reliably enough at the time and the built in decoder was not extremely helpful.

The other issue with an original QCX is that there is no enclosure option included with the kit. There is a great aluminum third party enclosure from BaMaTech but it is quite expensive and I had to wait for it to restock.

Also I was not confident I’m sending enough watts out to be heard reliably. In order to add some punch I was thinking about building the amplifier kit. It’s needed to key the amp from the transceiver and while I bought the kit I just couldn’t bring myself to solder needed wires, drill the enclosure and install PTT port into my QCX.

What’s cool about QCX+

  • The updated version does have an optional enclosure. The assembled rig looks rad IMO.
  • PTT port is built in.
  • CAT port is built in. Not that I care for SOTA but someone may find it useful.
  • You can connect a GPS module also available as a kit, calibrate frequency and sync time. This allows QCX+ to act as a WSPR beacon.
  • Yes, you can use QCX+ as a WSPR beacon! I find this feature very interesting because I want to know where I was heard even if no one got back to me. Also it may help to compare antennas.
  • The QCX+ board is slightly larger, less crowded than one for QCX and has component free margins fitting into enclosure slots. They also allow for an easier assembly using a board holder.
QCX+ main board with most components installed held with a board holder

QCX+ main board with most components installed held with a board holder

What’s not so cool

  • The QCX+ board is slightly larger, less crowded than one for QCX so rig dimensions are larger as well.
  • There is no built in speaker or battery - not that I need it but I need to mention.
  • I thought about installing the GPS module into the same enclosure but unfortunately it makes little sense - GPS module uses paddle input port to communicate with the rig and you can’t use both simultaneously.
  • Looks like I found a bug in T1.05 firmware - if you try to send a stored message sometimes the rig just beeps and returns back to the keyer speed adjustment menu. Beeps VERY LOUDLY. Like, eardrum busting loudly, be careful! I’m still trying to confirm if it’s a real bug though.

NB: Which band to choose?

If you don’t know which band to build for, I’d recommend 20 meters.

In my opinion a 20 meter band is the best for summer CW SOTA if there are no sun spots. General rule of thumb is to choose operating frequency about 0.8 * MUF (Maximum usable frequency). By getting as far as possible from LUF (Lowest usable frequency) we minimize absorption losses in D the layer. As of August 2020 there are no sunspots and maximum daily MUF hovers around 18 MHz making the 20 meter band a natural choice.

Because higher frequency signals penetrate into the higher layers of the ionosphere the length of ‘hops’ increases as well. Moving through the ionosphere a linearly polarized wave turns into an elliptically polarized one (This is by the way why polarisation of a receiving antenna is not extremely important). But each time a wave reflects from Earth a horizontally polarized component is being shorted. Longer hops => less reflections from Earth => less attenuation.

More than that - I prefer dipole antennas over verticals because the latter require a lot of radials to be effective on dry and rocky californian summits. Problem with portable dipoles though is that they are deployed way lower than at an ideal half wavelength height. My SotaBeams mast is about 6m / 20ft high. Since dipole is deployed in an inverted ‘V’ configuration the effective height is even smaller, about 5m / 16ft. Low dipoles aka “space / worm warmers” beam up (remember the recommended height for NVIS is lambda / 8?). As frequency increases the height of the same antenna measured in the number of wavelengths increases as well. This means instead of beaming straight up and losing a lot of energy in the soil dipole starts to radiate better at lower angles. Being on a narrow summit helps to increase an effective height further and squeeze the main lobes further down and closer to the horizon.

Kit assembly tips

I’ll try to avoid repeating the assembly manual for it is the best manual for a kit I ever saw - very easy to follow.

It took me about four evenings to finish the QCX+ and align it. I guess you can gulp it in one take - should take 6-8 hours from start to finish but why rushing things you enjoy?

The board comes with smd components pre-soldered, you only have to deal with through-hole components.

On the first day I wound and soldered the transformer and filter toroids. I prefer to wind / install all the coils first because it is easier to test your work quality before you add other components. If you put some components between coil terminals how do you know which path the tester current takes? What I like about the coil wires in this particular kit is that the insulation is very thin and does not require any scraping - just solder wires, test joints with a tester and heat a joint again if a tester does not beep. This is another reason to install coils first - why risk overheating other components?

Winding and installing toroids first

Winding and installing toroids first

On the second day I’ve soldered all the ICs and some capacitors. I recommend using an antistatic mat / bracelet just to be on a safe side.

Board with most IC installed

Board with most IC installed

On the third day I’ve finished assembly of the main board.

On the fourth and the last day I put together the front panel, assembled and aligned the radio. All needed testing equipment is built into the radio itself. Just a note - when installing a knob onto the rotary encoder don’t push it all the way in. It is a button and you’ll need some room to be able to press it.

Rig with the enclosure opened for alignment

Rig with the enclosure opened for alignment

Since I plan to use QCX+ with a 50W amplifier I made a suggested PTT jack conversion to be able to use a stock 3.5mm jack wire to connect the transceiver and the amplifier. Note the conversion puts +5V to the tip - something to remember if you plan on building a GPS receiver from the kit and powering it up from QCX+. Please refer to the manual for details.

Two cuts and two jumpers to swap PTT and +5V output

Two cuts and two jumpers to swap PTT and +5V output

Two cuts and two jumpers to swap PTT and +5V output

Two cuts and two jumpers to swap PTT and +5V output

While being marketed as a 5W transceiver it actually puts out around 3W on a 12V battery. I hope it won’t put too much strain on mosfets in WSPR beacon mode - the duty cycle is brutal, 2 minutes of a continuous key down. I believe everything is going to be ok though.

Output power is around 3W on 12V battery

Output power is around 3W on 12V battery

Output signal is clean enough and click-free as far as I can see with my toy oscilloscope. I was tuning around a signal from a calibrated signal source and it looks like the displayed frequency is actually about 50 to 100 Hz higher than the actual frequency the transceiver is tuned to. This is with the TCXO option installed. Looking forward to connecting the GPS module and calibrating more precisely.

17 WPM dit as seen on an oscilloscope screen

17 WPM dit as seen on an oscilloscope screen

As compared to other transceivers

With an enclosure measuring 14.7cm x 10.5cm x 5.5cm (5.8” x 4.2” x 2.2”) and weight of 562 g (1.24 lb) QCX+ is not the smallest and not the lightest transceiver on the market (surely one of the cheapest). 3W power output is quite humble as well. But it has certain features not available even in transceivers 10x times more expensive. I especially like the flexibility of the canned messages menu and the ability to modify stored messages. Saves a lot of time because you are not forced to pre-record your SOTA CQ sequence in one go as with Elecraft KX-2 for example. WSPR capability is neat and the documentation is superb. Hans provides a very detailed explanation of the QCX+ internals but if you are not inclined to increase your QNB it suffices to follow simple instructions and get your transceiver in the end.

Bravo Hans and thank you!

Front panel

Front panel

Back panel

Back panel

QCX+, QCX, Elecraft KX-2, Xiegu G90, Mountain topper MTR3B_LCD size comparison

QCX+, QCX, Elecraft KX-2, Xiegu G90, Mountain topper MTR3B_LCD size comparison

Stay tuned for the next SOTA report featuring newly built QCX+. For now this is it! 73 dit dit. K0SSK out.