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Welcome to the QCX Discussion Group! This has been created to (hopefully) corral all of the useful posts about the assembly, operations, and modifications to the QCX radio. All are welcome to post, but please keep these thoughts in mind: Be kind...no flaming...no superiority complexes need apply Keep on topic...no "...Oh look, a chicken..." posts No SPAM...no ads, no "look at this alternative kit", with one exception: If the item in question will SEAMLESSLY INTEGRATE with the QCX. More as they become necessary...not until, not unless Enjoy, Roland Stolfa (KC5UNL)

I would like to know if I can apply the following procedure to calibrate the Ref frq without GPS? Using a QCX+ 20M Band I would go to WWV 15MHz and read precisely the frequency for a zero beat. If I read 15.003.00 could I modify menu 8.5 to read 25.005.000 with the TCXO and have a more precise QCX+? 73 - Pierre - FK8IH Started by Pierre - FK8IH

A new member of this group, I'm receiving a QCX+ 20M kit next May with the following options: enclosure, dev board, TCXO, and AGC. I plan to use the dev board for various modifications: 4 internal LiFePo4 batteries, an internal LM386N amplifier with speaker, and possibly tapping the IQ signal for SSB and AM decoding on reception. Questions (I'm refering to the schematic published in the manual): 1. What is the frequency range in the 20M band for reception with a satisfactory sensitivity? 2. JP27 - are the VCC and GND voltage available at this location controlled by switch S1? (to power the LM386N circuit only when the QCX+ is ON) 3. DC In - I plan to connect the four LiFePo4 batteries to this connector to power the QCX+ when nothing is plugged into the DC In socket and recharge the batteries while using the QCX+ when the LiFePo4 charger (14.5V) is plugged into the DC In socket 4. JP18 - pins 2 and 3 output the audio signal only when headphones are not plugged into the headphone jack? 5. Is JP11 the right place to take the unfiltered IQ signal that can be used for SSB and AM decoding? 73 - Pierre - FK8IH

My 40 meter QCX mini has decided to quit on me. I bought two mini's ( a 20m one and a 40m one pre-wired). They both worked fine until recently when my 40m has come up with the message " use original IC". Since I bought them pre-wired, that should not have come up. Is there any easy fix for that or do I just write it off? Hate to lose it, but repair on these it not one of my abilities. Colin K4CML

HI all, I'm very surprised that when I plugged the PTT cable into my QCX, that it blew its 1A fuse and now smells badly of smoke. This was in preparation for connecting it for the first time to the 50W amplifier that I just built. Where do I start to figure out what to fix? Thanks, and 73, Andy KB1OIQ ..

Dear Folks: I have finished building the 50 watt amplifier kit for the QCX. I am trying to run the test on page 66 of the manual which simply requires you to do the following: 1) Make sure that the R5 potentiometer is fully counterclockwise. 2) Put the QCX in "Practice" mode so no RF is generated, but the radio will generate a voltage to key the amplifier. 3) After keying the amp via the QCX, measure the current draw between the amp and its power supply. 4) Once you have keyed the amplifier via the QCX and measured the amp's current draw, R5 is gradually adjusted clockwise until the current draw begins to rise. Once you see the current draw rise, you turn R5 back to the level just below the point at which the current draw rises. That is the correct setting for R5. I have done all of these procedures. I should mention that the green "on" light comes on when power is supplied to the amp and that the red TX light comes on when I key the QCX. The current draw measurement is 74 MA. Unfortunately, the current draw never changes even when I turn R5 fully clockwise. I should mention that I did try the same measurement with the QCX practice mode turned off, i.e., the QCX would now be generating RF. At that point I found that turning R5 gradually changed the current draw from about 97 MA to about 103 MA. However, no RF is generated (though the QCX generates about 4 watts when it runs barefoot). This makes me think that R5 is functional. Does anyone have any suggestions for locating the problem? Thanks and 73 de Bernie, KF0QS

Hi I've just logged in to get an updated firmware hex file for my QCX but the Files directory is empty ? Is there anything else I need to subscribe to to view and download from the Files directory ?

Hi, I was wondering if any other QCX+ builders has noticed this, my side tone note has a rough edge to it, it is not a nice clean note. It is RF getting into the audio side . I have tried suppressing everything attached ie, paddle, antenna and ear phones but nothing works so It seems to be internal. When in practice mode the side tone note is perfectly clear. This problem is spoiling my enjoyment of this lovely radio. Any help would be appreciated thank you.

Hi everyone, another question for you, my 40m QCX+, If I transmit on say 7.030 I am being received on a frequency which is 1.16Khz higher, why is this, am I missing something?

Hello to the group, I have just completed the build and am getting just over 2w out with a 13v supply, Can I ask anyone who has built the 40m version what you did to increase the power out up to 5w. L1, 2, 3 and 4 are wound as per the instructions. In Hans's video I notice on the 30m kit he adjusts the coils for an increase in power out, does this apply to the 40m kit and if so what adjustment gave you the best results. Thank you.

Hello , I have just finished my QCX+ and starting the adjustment procedure, The first adjustment is to adjust C1, I find that C! will not adjust the bar graph it is at maximum. I have checked continuity of T1 and that is ok, I may have counted the number of turns wrongly, would this give me the problem. Thank you.

I'm building the VFO/Signal Generator kit and am struggling to test the individual LPF's prior to assembling the kit. Not being the creative type, I don't know how to get SMA connectors on the filters without rendering them useless for the eventual kit. Thanks...Kevin AD0IM

Greetings. I am using a 75 ohm coax feed line to my antenna and would like to convert my QCX 40m transceiver to 75 ohms. Of course I could simply match the coax feed line to my 50 ohm radio, but why not make it match directly, rather than adding components? Researching the low pass filter on the output I see that it was optimized for 50 ohms, and if Im not mistaken, changing the numbers of turns on these inductors will accomplish the task. Not sure on the details, has anyone tried this? ...or willing to help with the calculations? Thanks in advance. AC1GX

Just finished building a QCX plus, but display is dark. I mean completely dark. Adjusting R47 has no effect whatsoever. There is plenty of voltage on R48. All suggestions welcome. Thanks, Steve

Dears, while assembling my second QCX+ now the 40m version after having finished the 20m trx I was remembering some discussions raised in the mchf build forum of the German "DARC-Ortsverband I40" while assembling the mchf SDR of om M0NKA years ago and all modifications leading to the fork of UHSDR that was/is in developement by the mentioned ham group. Some discussed topics are focused on the proper value selection of the QSD capacities (C43-C46 in the qcx+ pcb rev.2) as well as the optimal voltage value provided to the FST3253 by the center tap of Tr1 that is divided by R1 and R2 from the +5V. (In the case of mchf is was 1.8V and not the half of +5V as used by Hans.) Due to this old experience and the fact that the qcx+ as well as the qcx are mono band trx I'm looking for the best values to provide for every band in order to get the highest sensitivity and the highest resilience against strong input signals as well as the best IQ balance and side band suppression. Perhaps this discussion was already done and I'm to late in time but would you like share your opinion on this topic as well as your ideas and experience. Many thanks in advance for your effort. vy73 Markus DL8MBY

Some time ago I purchased a QCX Mini and a QRPometer (NM0S). After receiving them I discovered my eyesight and finger dexterity would not allow me to assemble these kits. My last assembly project was a DX -40 in 1957 hi. I seem to remember a group member who volunteered to do assembly for people in my situation. If he is still in the group, or if anyone else would like to help me out, please respond. I would really like to get this on the air. Thanks! Jim, W4VJ

Dear Forum, any hints how to overcome the mentioned problem above? I used an ISP programmer named T48 (TL866-3G) Has someone the proper EEPROM and Fuse content to share. BTW I wrote an email to Hans Summers (QRP Labs) but posting this issue in parallel in this thread in the case someone could help too as Hans is busy with his projects. Thanks in advance for your effort and help. vy73 Markus DL8MBY

Apologies for minor topic. Trying to avoid congested in box in gmail. I did set this up a long time back but settings didn't get carried over when my new phoned was cloned over and have forgotten the process. My main problem seems to be identifying the address/domain name to select the QRP labs mail messages. 73 Mike 9V1LX