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Qcx qrp rig

Gave my QCX a little try on air this afternoon.

30m doesn’t seem very lively but I was happy to work S57V, receiving a 559 report.

According to my QRPometer, my QCX was putting out 3.5 Watts whilst running from a SLAB supplied by 2E0YYY many moons ago.

I don’t think 30m is feeling very happy today!



Ran my newly completed QCX 30m rig yesterday afternoon on 30m WSPR (1 watt into the coax), Spots from much of Europe down to EA8, Asiatic Russia, VK5 and VK7. Looks like it is going to be fun to see how far I can get with CW when I get a chance this weekend


Well, the problem with my QCX was the 560pF capacitors C25 / C26 in the low pass filter.
I have replaced these with new components of the same value, and now, having gently tweaked the turns spacing on the toroids, I get over 2.5W with a 12v supply, and almost 5W with a 15v supply :smile:

The symptoms are discussed on the qrpLabs groups.io forum, in a thread titled “A word about QRP Labs capacitors and toroids”, started by Hans, the designer of the QCX.
It looks as though there might have been a bad batch of caps affecting the 20m and 30m low pass filters (though Hans is still investigating).
Typical symptom is that the power output creeps up over a minute or two with key down. I think this is because (a) the capacitors are a bit lossy and so warm up when in use, and (b) they are not NP0 as they should be eg the value reduces with temperature increase (I can demonstrate this with the removed components), shifting the cut off frequency of the filter.

Anyway, an interesting diversion, an easy fix, and a nice end product!



I’ll have to build mine now. Mind you it’s not been lurking for long enough. Took me 5 1/2years to get my K2 sorted! I must take that on an activation now… they’re big though.


+1 Adrian. My 20m QCX had the exact same problem, and replacing those caps fixed it. Just did this on Saturday.

Even with the bad caps in there and only getting around 1.5 watts out, I still managed a SOTA activation where I made almost 20 contacts (one of which was Japan). The rig should really be ripping it up now, with 2.5 watts @ 12V =)

P.S. here is what I did for a case on my QCX:


Got that box from Amazon - its got a rubber gasket so should be very water resistant. It tends to rain a lot here in W7W, so this should be a good foul WX SOTA rig.

-Josh WU7H

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My 60 m QCX in an enclosure form QRP labs, worked fb during my latest activations in FL/NO.


Very nice. I got my 40m QCX kit & enclosure from Hans in Friedrichshafen and I am looking forward to build it. I like the CW paddle attached to the housing. Please write some more info about this CW paddle. Thank you.

73, Milos S57D

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Dr OM Milos,
The paddle is a kit from QRP Guys mounted on a 2 mmm aluminium strip with slot holes under the screws on the front of the enclosure.
73 de geert pa7zee


Hi Andrew, what do you mean by the right learning method? I would like to what they are.

73 de Geoff vk3sq

Hi Geoff,

I think the right learning method varies between learners, as I read of different people having success with different methods. It would be trite to say that the right method is the one that works (for you) but that is what it amounts to. if someone tries the Koch method and finds it is not working for them, they need to try alternatives.

I don’t like the Koch method myself. I think it builds memory pathways that are undesirable. Eg I find people mixing up G and U and it makes me think they learned by a method that involved remembering combinations of elements (dots and dashes) and those combinations remain associated with each other, whereas learning the sounds and going directly from sound to letters is more effective in my experience.

It needs to be treated as seriously as one would treat learing a language. You are training your brain to do something it has not done before, or for those who have tried before, unsuccessfully, they are having to unlearn some complex (long) pathways and relearn correct ones. There is a video in which the letters are shown on scrren as dots and dashes. My advice is never look at it. That is telling your brain to translate from a sound into dots and dashes, then convert that to letters.

And just as you are tested when learning a language the learning method needs to test and retest the student’s memory. Whereas listening to it and saying you know the entire alphabet does not test you.

I won’t go on. Hopefully this is enough to illustrate what I meant.

73 Andrew VK1DA/VK2UH

Interesting on your Qcx, I’ve a 30m kit on the way to go in the QRP Labs enclosure !
Did you, as you said in your post, worked on 60M from FL/VO ?
All yours QSO, if you TXing on 60m are invalid, you know 60M is not allowed in France…
Maybe I not understand your post :wink:

Hello Eric,
You are right!
Geert uploaded only one 5MHZ QSO (S2S) with DL2AP/P.
73 from Gerald

Dr OM’s Eric and Gerald,
My mistake. I did not know that 60 m is not allowed in your country. I will delete this QSO.
Thank you for the information.
73 de geert pa7zee

A thing to be considered before ordering it:

From the order to the moment the rig arrives it will pass at least 2-3 months.
I’ve bought the QCX serial 5066 a month ago, ad now they are delivering the serial 4050…
Enough time to learn cw better!!

73 de in3aqk

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I started building my 80m version a few weeks ago. There are 83 turns on T1 in total, which meant there were lots of overlaps of the windings. That’s not a problem in terms of how the rig functions, but it makes it impossible to count the turns once the toroid is wound. After emailing Hans, I rewound the toroid with 0.15mm wire, which goes on in a nice single layer:

Besides looking a lot neater, I was able to mark every 10th winding with a permanent marker, which helped me keep track of all those windings. I’m waiting for the GPS board and the 80m LPF to arrive now (I bought the 40m version in Friedrichshafen the changed my mind last week).
73 de OE6FEG M0FEU


I finally finished my 80m version this morning:

Power out is about 4.35 watts at 15v, which will do me. Apart from a duff microcontroller, everything worked first time. If I were to do anything differently, it would probably be to check the inductance on the main (68 turn) winding on T1 before installation. The bpf variable capacitor is almost completely open:

This suggests that there is almost too much inductance; perhaps a consequence of having the windings neat and tightly bunched up. But with all the connections possibly needing to be re-done, and thus solder to clear out of the holes, I don’t want to try removing a few turns. The signals seem pretty loud so I’ll leave things as they are for now. But some way of measuring inductance would be advantageous with this kit. I’ll order the enclosure this afternoon.
73 de OE6FEG

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If you are concerned that the variable capacitor is almost fully open, you could reduce the fixed capacitors in parallel. I would leave it alone!

If you get two peaks when aligning the Rx, with the second peak about 60 degrees clockwise of the position in the photograph, then everything is fine.


I do. Thanks for the input.

I have built two QCX kits - for 20m then 40m. Both work a treat.
The only issue I had with the 20m kit was that sidetone was not very good (a lot of clicking and delayed). When I built the 40m kit, I noticed Hans had modified the design slightly. Changes included the 10uF electrolytic coupling capacitors either side of the AF Gain potentiometer. These capacitors (C21 and C22) had been changed to 1uF multi-layer ceramics. This resulted in greatly improved sidetone on the 40m kit. So, I ordered a few extra 1uF ceramics and did the same mod’ on the 20m kit. It worked - 20m kit sidetone is now perfectly acceptable.

Only other unusual thing worth mentioning is that the 40m kit was initially putting out 10W RF power on 12V supply. I was worried this was way more than the manual suggested and I wanted the rig to be proper QRP with 5W or less. All I had to do was squeeze or “bunch up” the torroid windings on the LPF inductors a little bit. This increased their value and brought TX output down to just under 5W.

Very happy with both kits. Maybe need to get one for 30m next?

i have a 30m kit. . . . . still in its box. I will get round to it. . . . . eventually.