RaDAR – QCX Audio

I think I have sorted out all the QCX alignments which are quite simple to do and appear to be correct. I feel I did a good job during the build process and have used the little rig a few times trying to get the feel of it.

I’ve made peace with the fact that it is a well designed modern receiver that is filtered to the maximum (200 Hz). It does receive signals but the purpose of this Blog is to share my experience of the audio. My QSO with Z21GC last night was a good example.

I have tried various headphones but the audio is not sufficient to drive them to a comfortable level. I’ve used my cell phone earphone with limited success. I also used a PC’s shoX powered speaker and that is what I used to complete my QSO with Brian last night. I held the speaker close to my ear, constantly adjusting the volume control as the signal had deep QSB. The audio amp can be easily over driven and the distortion can be heard almost sounding like a 555 oscillator. If you cut back on the audio it sounds more pure but then it’s a battle to hear properly.

It appears there is no AGC (Automatic Gain Control) so there is a constant fiddling with the volume control to prevent overdrive. Certainly a lot went into the design of the QCX. It’s a modern style rig and the TX is really awesome …. Oh that reminds me …. I noticed, on key down, the sidetone audio level gradually gets less, the signal indication gets less which appears to be essentially an audio level indicator in it’s standard configuration.

I checked my supply voltage and it’s reasonably constant. I put my home brew dummy load / QRP Power meter on the output and it stays constant but as explained above, the sidetone audio levels gradually get lower. You don’t notice it while sending CW only on key down for a few seconds.

A lot has gone into the design of this rig but the audio falls short of my expectations which builds up frustration. But, I’m a “die hard” I’ll be back hoping there is something I can do about it.

I have a spare 49er board which I may use for the audio section only and hook that up to the QCX.

                                                                   The QCX’s Audio output stage


It will be a simple task to wire the 49ers LM386 audio amp via the volume control pot. The 49er doesn’t have a volume control either! Then wire the power supply in parallel with the QCX’s


           The 49er’s Audio output stage


Update 2017-10-27

I built the audio and power supply sections on the 49er board and did the tests.

The LM386 isn’t the quietest audio amplifier you could ever use which probably explains why Hans didn’t use it in his design but I can hear what I need to hear now even if it’s mixed with the LM386’s “Hiss”. The headphones I use now have sufficient drive for comfortable listening and I simply still use the QCX’s volume control for comfortable listening level.

Without wanting to be invasive I used the standard QCX audio output and fed that into the LM386’s input. No RFI …. there is sufficient filtering on the 49er circuit.

So, I’ll make this a permanent solution to my QCX problem for the time being.

Update 2017-10-31

Last night I wired the 49er audio section to the volume control of the QCX which is just before the QCX’s audio section. The audio is lively!!! More than enough. So it appears that there may be a fault in the region of IC10 on the QCX board as reports worldwide say that the QCX has quite sufficient audio to drive headsets or whatever you use to play the sound.

It wasn’t a waste of time doing this for once I do manage to find and fix the fault I have an alternate audio port for recording or even for a public address facility!

I am still concerned about T1 and the band pass filter peaking. I get a peak but don’t see the peak drop while turning C1 before it’s unmeshed again. I may have to further reduce the turns on the toroid one turn at a time. Maybe I’m close to resonance but not exactly there. I doubt it though that that be the cause of the audio levels of the QCX. The 49er addon proved that I think???

73 de Eddie ZS6BNE


RaDAR – Purpose driven amateur radio

I’ve been though a few decades of this (42 + years), had a son who became a ham and is no longer one, have a grandson who has won book prizes for youth day participations but no interest, actually I think it’s the influence of ouma!!!  

Actually ouma hates the hobby for what it maybe does to me, I become very mission driven. You see I use QRP 99% of the time with simple wire antennas. I spend hours perfecting the right combinations.

Recently very involved with building CW transceivers which I believe every ham should be capable of doing.

There should be a purpose to it all. I spend hours in preparation like on Saturday, various configurations and propagation opening it’s own roads, just for one brief contact and the XYL see’s that “driven” attitude … a will to succeed. The battle is not always won … but sometimes it is …. it gives me strength to fight the next.

Yet, my young grandson can sit for hours browsing the Net, watching You Tube …. complaining if there’s a “mother-buffer” while using Kodi and video streaming.

If you want to be a ham and stay a ham you must be prepared for the worst, a battle …. the greater the battle the greater the satisfaction when won but few stay to see the end …

That’s why I promote RaDAR, it’s the purpose thing that drives me and with each outing I come back having learnt something new.

Totally without further energy, like being through an adrenaline rush – yet few understand why …. yet they know I’ll be back in a day or two.

It’s not about the contacts, the ragchews (for me anyway) it’s those brief moments of success attempting the near impossible yet it is possible if the mixture is right.

I don’t have all the answers but certainly forums and discussion groups help. It’s a very touch and go lifestyle now, ham radio for me is touch and go too, make the contact, pass the necessary info and move on …. success.

RaDAR – Back to the bench for the QCX

John ZS6JBJ was pounding in from an odd 250km away on Saturday. I recall the QCX deciphering the morse code it was receiving, John giving me a GENUINE 599 too. The QCX’s Class E transmitter is really awesome! The odd 3 Watts does very well.

Then the QCX’s audio started sounding a little shaky and gradually it disappeared yet the alignment tones can still be heard when switched on?

So, it’s back to the workbench this week. Luckily I have a reasonable RF generator so I can feed the QCX with a signal and try and find out why it no longer gets to the earphones ….

Maybe the 49er wants a turn on 7.023 again !!!

Update 2017-10-17

I fed a 1 mV signal at 7.023 MHz into the receiver, it’s still receiving! I’m used to a noisy receiver with no filters, this rig’s RX is only 200 Hz wide and QUIET! If it hears a signal then it plays the sound – 700 Hz CW. SSB of course is unintelligible, this is a CW only rig!

I heard ZS5CEV (If I recall correctly) calling CQ and he was strong, I answered but he did not come back. I was using one of my 40m end feds which was probably not optimally tuned.

Well that is good news.

The bad news is that the band pass filter peak adjustments look suspect, I may have to add or remove a turn or two on T1 – my biggest nightmare! The adjustments need to be made without an antenna or dummy load!

RaDAR – Operating the QCX 40m 5W CW transceiver

On Wednesday the 11th October 2017 around 17:50 local time (15:50 UTC) I had put up my home brew 40m end fed in the back yard. It was time to take my newly built QCX for a walk. Fortunately I tuned around and heard Daryl ZS6DLL calling CQ on 7.020. Excited with the prospect of making a first QSO (I had just managed to complete the alignments), I called Daryl and he heard me first time!!! Daryl gave me a RST 579 and he was a good 599.

I came back an hour or so later to call CQ before packing up and today after clicking a link to the RBN on my laptop, found that I had been heard in Namibia and at 12 dB!!!

Wow! Not bad for around 3W!!!

I found a protective carrying bag at a music outlet and for the time being I will carry the kit this way. Hopefully I will be able to make a few more QSO’s this weekend!



RaDAR – Building a QCX 40m 5W CW transceiver

After having success building a 49er and using it, I was offered the QCX kit from a local distributor at a reasonable price. I also had already successfully repaired my HB1A so it was a financial decision I had to make. Fortunately it seems I made the right decision to build yet another radio. The QCX impresses me more each day!!!

It has been a few evenings hard work and INTENSE concentration but I’m almost finished. Fortunately I had a week’s holiday in between so I could come back with new found energy.

The toroids are in too just the four winding toroidal transformer remains to be built and installed which I will do this evening. Then a few controls need to be put into place then it would be time to power up and start with the alignment!!! That should be the cherry on the cake 🙂

Some pictures from where I started … Fortunately the two tiny SMD components are factory mounted!

This could form an ideal RaDAR Paraset for 40m CW only ops!!!