QCX QRP Portable Transceiver Build

This compact “QRP” or low power radio kit from QRP Labs in UK was too good to resist.  At $49.00 USD, it packs a lot of functionality into a small package.  The radio is based around an IQ phasing receiver for CW (morse) and an Class E efficient transmitter.

The transceiver includes built in alignment software and hardware, a WSPR beaconing mode, CW decode and internal memory keyer.  See the QRP LAbs site for the details.

The software alignment is most impressive as is the well thought out menu structure.  I chose the 20 metre band variant when ordered.

The radio looks ideal for lightweight SOTA operations.  As the kit is supplied without a case, some thought is needed to package it efficiently.  This plastic enclosure from Jaycar fits quite nicely with a little space to fit a 3 cell Lipo pack.  There is still some work to do around fitting the two pushbuttons, volume and tuning encoder.

A shaft extender will be used from the encoder shaft through the top panel.  The volume control and two push buttons will be top panel mounted and cabled back to the board via a connector.  I had to cut down the supplied board stand-offs to about 8mm long with a Dremel so that the display was the right height to sit behind the top panel.

Nice fit of QCX and battery

Top view without controls










RHS panel with BNC and paddle socket

LHS with earphone socket







A shaft extender for the rotary encoder was turned up on the lathe.  I could have probably bought one, but this one is small and light.  A bush from an old pot might be placed on the top lid of the case for a bit more support of the shaft.  It doesn’t feel to bad though.

Shaft extender

The controls have now been fitted without problems.  It was nice that there are connector pads for off board controls.

The radio looks a little off balance with placement of controls now, probably not helped by the extra space above the display.  The DC screw terminal connector had to be removed as it interfered with the side panel of the enclosure.   A barrel type 2.1mm DC bulkhead socket is fitted to the side panel for power in.

A bezel of some sort is needed for the display to protect it and improve the appearance.  For internal batteries, the 3 cell Lipo fitted ok, although I have settled on using 3 x 18500 round cells instead.  These cells take up a bit less space and are more robust.

Controls Fitted


It is still work in progress.

The RF power output had a tendency to immediately go to about 1.5 watts and then slowly rise to just under 3 watts from cold.  A quick re-ptt saw the power go about 3 watts on 14.020 MHz.  If the rig was rested for 10 seconds or more, the power would go to 1.5 watts and slowly rise again.

As suspected, it turned out to be capacitors in the low pass filter.   One by one the capacitors were replaced and the RF output behaviour checked.

There was no change when the outer 2 x 180pF (C27+C28) caps were changed, but a noticeable change when one of the inner 390pF (C25) was changed and then perfect when the other 390pF (C26) was changed.
I changed each cap with a 250V ATC ceramic chip cap.

The output power is now very stable and the supply current has dropped.  Output is 3.5W with 13.8V supply.
I took a turn off both L2 and L3, so L3 is 15T and L2 is 16T and output is about 4W.

I also experimented with the 30pF capacitor from the drains of the finals to ground.  The efficiency went up slightly without it.  I put a 30pF trimmer in its place and found best efficiency at almost no mesh of the trimmer.

1500mAh 18500 cells

This photo shows the 3 x 1500 mAh 18500 lithium cells fitted.  A balance connector is connected to the cells.

After running a WSPR test, the power output and current consumption became erratic.  Sometimes it would draw 1000mA and transmit only half a Watt and other PTTs it would draw 450mA and put out 4 Watts.  Q6 was also getting very hot.

Q6 was replaced and it completely fixed the problem.  Q6 is on the limits of its ratings.  It looks like Q6 has been replaced with an MPS751 is later versions of the kit.


I had noticed that the first PTT after power up resulted in a high current draw and low power output. This behaviour was completely repeatable after every power up.  Others on the forum (Olgierd SQ3SWF) also had some issues with RF output changing from PTT to PTT as I had previously experienced.  Olgierd had noticed some RF or possibly oscillation on the gate of Q5 when the radio was transmitting low power out and consuming high current.  I put the scope on my QCX and noticed that also, on my first PTT high current, low power out condition there was some RF on the gate of Q5.  It seemed that Q5 was shunting RF into the front end in this condition.

A 4k7 resistor was placed from +12V to the drain of Q5 and in my case the first PTT issue was completely resolved.  About 30 power cycles were tried with no recurrence of the issue.

4k7 resistor on back of PCB


See photo for placement of the resistor.  Also note the SMD low pass resistors that were replaced.




Programming the processor with new firmware:

  1. The .hex file is downloaded from the files area on QRPLabs groups.
  2. Download Extreme Burner for AVR.  Its a bit tricky to find where to download this on the website.  There seemed to be adverts everywhere.
  3. Obtain a USBasp programmer from Ebay or similar.  Mine didnt come with a lead from the USBasp programmer header that fitted the QCX programmer header, so I had to make one up.

    Lead from USBasp to QCX


    4. Install the Zadig drivers.  I can’t remember doing this, it must have already been installed on the PC.

    5. Put the header on the QCX and plug the 10 pin end into the USBasp and plug the USB connector into the PC.

    6. Start Extreme Burner.  Choose ATmega328P under “Chip”.

7. Go File>Open Eprom File and browse to the downloaded QCX hex file.

8. Click “Write All” and that’s it.

Posted in Projects, radio communications, SOTA | Tagged , , | 9 Comments

CW Paddle for the KX2

I came across this KX2 paddle from the QRPGuys recently.  The price was right at USD 25.00, postage was USD 5.00, so quite a bit cheaper than the original one.  It’s made from soldered PCB material so it won’t be as robust, but it seems to work just fine so far.

It took about a week to arrive from ordering, I understand that they do their mailing on a Wednesday.

The instructions downloaded from the website were clear and straightforward, construction took about an hour.  Right at the start, it’s important to line up the PCB rear and sides nice and square before tacking together with solder.  Apart from that, the only fiddly bit was getting the screws, washers and spacers in place to hold the paddles in place.

At first it felt a but strange to use with the flexible paddles, but you get used to it pretty quickly.

I will report back when it has been used on a SOTA activation.  

It probably needs a cover for the paddles when it’s not in use to protect it from backpack rash.
For the moment, it is wrapped in some EPE foam.

Posted in Projects, SOTA | Tagged | 4 Comments

Toorongo Range VK3/VT-026 Again

With freezing temperatures although clear skies, it looked like this would be one of the last times to get to a winter bonus summit for a while (or so I thought).   The ice was removed from the car and I departed for Toorongo Range.  I have been to this summit several times before, it is not really one one of the favourites although access is very straight forward. There is just a short walk up the Toorongo Track from the closed gate and then a bush bash scramble to the summit.

The drive there is through Noojee on the Mt Baw Baw Tourist Rd and before Tanjil Bren, take the Toorongo-Tanjil link road to the left.  Some six km in, take the Mundic Rd. and then the Toorongo Track.  This time of year, there is a gate about 1km short of the highest part of the road where you scramble through steep bush to the summit.

On turning into Mundic Rd, snow appeared on the road which gradually became heavier on the Toorongo Track.  The road is pretty good for a track classification.  The car was parked about 100m short of the gate where there is a bit of space.  The weather was holding out and things looked quite nice with the snow, much more interesting than the previous summer activations.

The bush bash up to the summit was straight forward, without slipping over like last time.  The summit is on a rocky outcrop with a small cairn.  Just behind the summit, there is a sheltered spot with some good tree cover.  I used this spot once before during high winds and ran some coax out to the antenna.

Contacts were made on 40 and 10 metres in great sunny winter conditions.  As expected 40 metres was behaving pretty badly.


Summit Cairn and Elecraft KX2 Station


Sheltered area behind summit


Sheltered area


Behind the summt


The short log!


Posted in Hiking, SOTA | Tagged | 4 Comments

Takatoriyama JA/HG-252 SOTA

Following on from the previous post, the other close by summit was Takatoriyama.  This one looked very close on the map.  Occasionally, we had seen hikers going past Meagan’s house so it looked like this was the on a popular hiking route.
The SOTA radio gear was put in the pack and we headed up the road.  At the end of the street, it looked like a dead end.  I was about to turn around, when a really old guy hunched over yelled out and pointed to some steps at the end of the street.  The steps looked like they were on someones property.  He shuffled over and gave directions is Japanese (that I could not understand), but I got the general idea with hand actions.  It must have been my hiking gear that made me look like a lost hiker.   I thanked him and we continued.

Park with Sakura

We went up the stairs and then to a lane and at this point, my mapping application (Maptrek with Open Street Maps) showed a dotted line.  The track continued to a small park with a playground and then to the right there was a hiking trail.

At the start of the trail a sign warned of the dangers of wild boars in the area.  We didn’t come across any but there was evidence of digging along the track, not sure whether the boars were responsible!

Wild Boars!

The walk was reasonably steep with some really great views along the way.  We saw many other hikers on the way and practiced our greetings as they went past.   About a km in, there was a sign to the summit with the altitude in metres.  We turned left up there.  The track went past a small clearing (an ideal SOTA location) and then to a small walled area at the back of the shrine.

The trail to the summit


I went back to the SOTA spot and tied the squid pole to a tree.  For the antenna, only the 15 metre section of the End Fed Half Wave was rolled out due to space constraints.
The noise floor was very low which was encouraging.

SOTA location

After a CQ as JP1PBQ, a few JA stations came back.  Shortly after I worked ZL1BYZ and  then VK7CW which was a nice distance.

I also worked 9M6BOB in Borneo with very strong signals both ways, it must have been the sweet spot for propagation at that time.

Weather was holding out, so the station was shut down and we went over to the first shrine we saw and had a look around.  The guy care taking the shrine gave us lots of information on other hiking trails and the shrine itself.

It was in Japanese, so relied on translations from my daughter.

Shrine before the summit

This guy must get cold

The hike back was uneventful, although just as we got back to the street, the rain came down, so another nicely timed activation!

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Yokooyama JA/HG-255 SOTA

While on holidays in Japan, we spent a week in Kobe staying at my daughter’s house in Myohoji.
After some emails with Toru, JH0CJH, I found that a few close by summits had been added to the SOTA database.  These were Yokooyama JA/HG-255 and Takatoriyama JA/HG-252.

Despite predictions of rain for the day, I headed off early from Myohoji on foot for Yokooyama.  The best route wasn’t too clear from the maps I had, but it did seem the approach was from the west side.
For navigation, I used Maptrek for Android which was loaded with JA/HG summits as waypoints using Openstreetmaps.
After a few km of roads, I came across a steep section of steps that looked like the right way to go.

The weather held out on the walk and soon I was in fog with limited visibility.  There were a few options of tracks, but Maptrek was showing that I was going in the right direction and after a few km, I arrived at the summit.
I had the summit to myself, which was great, so I put up the squidpole and bungied it to a tree.  The 20/15/12/10 metre End Fed Half Wave was reeled out.  When the rig was connected, there was a constant S5 noise level on 15 metres which was going to make things difficult.

After a couple of calls as JP3PBQ, I worked ZL1BYZ which wasn’t too bad despite the noise levels. After John, I worked a few JA stations and qualified the summit.  The fog still hadn’t lifted which was a shame as there would have been great views.
On the return trip as the elevation dropped, the fog began to clear and reveal some nice scenery.
The walk back was uneventful although I did leave my walking pole behind at a shelter at the bottom of the steps and had to retrace my steps to recover it.  The predicted rain started to fall, lightly at first and then became quite heavy.  By this time I was near a Lawson Konbini, so I sheltered there with something to eat for a while.

On the return trip, I recorded the walk with Maptrek and later overlaid the GPX over Google Earth.  The plot shows the walk ending at Myohoji railway station.

Posted in Hiking, SOTA | Leave a comment

Mt Halla (Hallasan) HL/JJ-001 SOTA

While on Jeju Island, South Korea, a hike and SOTA activation of Hallasan, HL-JJ-001 was too good to pass up.  Hallasan is the highest summit in South Korea at 1950 m high.
Sarah and I made an early start, leaving the hotel about 5am in Seogwipo, allowing an hour to get to the car park.  The driving travel distance was not too far, but it takes longer than you think to get around in Jeju Island due to speed limits, traffic and indirect routes caused by a volcano in the middle of the island.
We chose the Seongpanak trail to the summit, noting that you have to be at the last checkpoint before 12:30pm to be permitted to continue to the summit.

We arrived at the Hallasan car park just before 6am and the sun had not yet risen.  The car park was emptier than I had imagined, I guess it was a weekday (Thursday).  Our little Kia Ray rental only cost 1000 won to park (about a dollar), a normal size car would cost more.

The hike is 9.6km each way and starting at an elevation of about 750 metres and rising to the summit at 1950 metres.  I was hoping to arrive at the summit around 0100 UTC as this seemed to be the best time for radio propagation to the VK and ZL.

As we began the walk at 6am, the sun was just rising.

The hike is pretty straight forward, although there are many sections of large rocks and it got quite hard on the ankles.  Sturdy hiking boots are a must.
Some sections are board walks which is nice and others are stepped sections, either of rock or timber.  There are two main shelters on the way with toilets and indoor space to rest.  The weather was perfect, no wind and some sunshine.  The temperature must have been below zero on the ascent as there were ice needles rising from the ground and sections of solid ice in places.  There were also some drifts of snow along the way.

We arrived on the summit at 10:10am, which was very good time and on air by 0115 UTC.  I chose 15 metres for HF as this seemed the best band for South Pacific DX.

 Luckily there weren’t many on the summit at this time, so I set up without worry of being in peoples way.  The squid pole was bungied to a rail post and the End Fed Half Wave tied off to a hand rail further along.

I only had the FT-817 barefoot with 5 Watts, so it was going to be challenging for longer distance contacts.
After a couple of calls as HL1ZIB, John ZL1BYZ came back which was a relief.  John’s signals were good and clear above the low noise floor, he gave me a 3×1, but signals were rising.  Peter, VK3PF came back next, again with marginal signals at his end, but a contact made.  VK7CW came up with a nice signal and then I went to 2 metres for a local contact with HL4MC.  Returning to 15 metres, ZL2IFB was quite strong, and gave me a 5×5 and it seemed signals were still improving.
At this point the summit was qualified and there were a lot of hikers starting to arrive, so thought it best to pack up and get out of their way.  A couple of hikers were asking in broken English what the radio gear was for.  I explained best I could, one of the guys knew about amateur radio.

At the summit there are fantastic views and a lake in the crater of the volcano.  There was a bit of snow in the crater as well.
We had an early lunch and decided to leave as the traffic up the mountain was increasing.  The trip down was made difficult by the number of hikers coming up the mountain and trying to make space to pass.  Some of the icy sections had become very slippery and I went for a slide on one of them.

Arriving at the car park, we went straight to the shop and had a big drink.  I had used 3 bottles of water on the trip.  The temperature was quite pleasant at the car park, probably around 16 degrees or so.

It is a great hike and glad the activation worked out OK, sorry Sarah about the longish walk!

Posted in Hiking, SOTA | 2 Comments

Quick Trapped 15/20m Dipole

This dipole was a last minute idea.  I am taking a multi-band EFHW and 10/20/15/12/10m switched dipole away to Japan, although the switched dipole takes up a lot of space.  A smaller dedicated 15/20m dipole would be a good idea.

In the junk box I had some T50-6 cores.  The only high voltage capacitors I could find were 100pF ATC SMD parts.   To make a 15m trap, 11 turns are needed according to the formula on toroids.info.

The toroids were mounted on some single sided PCB.  Two holes at each end of the PCB strain relief the wire connection to the traps.  As time was short, the PCB foil was dremel’d away to suit the connections.

The traps were tested using a coupling loop to the homebrew antenna sweeper and with a little squeezing, they tuned to 21.1 MHz, a sort of compromise.

The toroids were then soldered properly on the PCB.  For a starting point, a 3.4 metre length was used for the inner wire and a 1.7 metre length used for the outer wire (away from the feed end).

The lengths were based on about 5% less than half wave.  The lengths needed a bit of trimming, first resonating the inner length for 15m and then trimming the outer length for 20m.

Before covering in heatshrink

The homebrew antenna sweeper was used for tuning the antenna.   The 15 metre bandwidth is quite narrow, below 2:1 between 21 and 21.25 MHz.  About 1.5:1 mid way.  This is a bit narrower than I wanted.  The 20 metre bandwidth is fine with a good match between 14 and 14.3 MHz.




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