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I recently received my assembled QMX+. It is a very neat transceiver, well designed and nicely built. I have played with the USB, reading the IQ samples from the 20-bit, 48-kHz ADC. The QMX+ is in CW mode and IQ is enabled. I cannot find information on the architecture, but I guess it is like follows. The antenna signal passes through the bandpass filters to the Tayloe detector. The frequency to the mixer is the dialed frequency minus the IF frequency of 12000 Hz minus the side tone frequencey of 700 Hz. If I dial 7020 kHz the mixer will use (7020000-12000-700) Hz = 7007300 Hz. The resulting product passes through an amplifier with a lowpass filter in front of the ADC, about 24-kHz bandwidth. The sampled signal has two channels, I and Q, real and imaginary part. These signals, which have a bandwidth of ±24 kHz, are available at the USB port. If I listen to a CW signal tuned to 7020 kHz, it appears as a +12700-Hz signal on the USB port. The CPU in the QMX processes the signal by mixing it with 12 kHz (complex sine, exp(jwt)). The resulting signal, I/real part only, (appears at +700 Hz), is then passed through the CW bandpass filter, nominally adjusted around 700 Hz. I have attached a PDF sketch of my understanding. Is this description correct? I experiment with a configuration where the CW filter is a (IQ/complex, two equal channels) Gaussian low-pass filter around zero frequency with a bandwidth of 10-50 Hz. This corresponds to 20-100 Hz bandwith in a bandpass configuration. Consequently, I mix the USB signal with IF+ST, before feeding it to the filter. The LP output is then mixed with the ST frequency to the speaker/earphone. (Note that zero beat is not useful in the analog implementation due to noise and bias.) Best regards Anders, SM5KAE PS I get some tiny spikes 1 kHz apart in the FFT of the USB data. Are these generated in my setup? DS

Hi My reader is very erratic with a lot of *. can someone who has a good setting let me know how they are please -- Martin DK3UW

I have noted that my RTC is wildly inaccurate, gaining 7 minutes overnight. I have removed it from the display...do not really need it. Does anyone know if the GPS module disciplines the clock or VFO frequency ? de VK6XT

One of my BS170's fried yesterday, and I am replacing all 4 of them. Using the excellent info at /g/QRPLabs/wiki/37486 , I am trying to determine if other components were damaged. I have removed all of the BS170's , and looked at the signal coming out of IC503. The voltage levels are okay, but it's neither a clean sine wave or square wave. Is that okay ? Thanks and 73, Steve, N2IC

Somebody asked me how I access the QMX terminal settings if the radio is connected to a headless Raspberry Pi that I can connect to only with a text based ssh connection (or through a browser window with ttyd). Without a graphical desktop system, tools like Putty don't work. So, here are some notes on using GNU screen for this. GNU screen is a text based terminal multiplexer that is widely available on Linux machines. If it isn't installed on your raspberry pi, you can install it with 'sudo apt install screen'. I often use it so that, after I connect to the pi using ssh, I can create multiple windows (tabs) that I can switch between to run multiple programs. If my ssh network connection to the pi is closed, programs running in screen windows (like ardopcf or pat) continue to run, and I can reconnect to them later. See 'man screen' or various online articles and videos for a description of this normal usage. A less well know use of screen is to connect to a serial device with it. So, if the QMX is connected to the pi with a USB cord, so that it appears as virtual serial port '/dev/ttyACM0', you can open the QMX terminal using the command: 'screen /dev/ttyACM0'. Just like when connecting with Putty, this displays a blank black screen until you press <Enter>, and then you will see the QMX terminal menus. Keyboard input including arrow keys should then work as expected. However, there are two things that are different than when using a program like Putty. First, Ctrl-Q, which Hans chose to use to back out of various sub-menus and screens, does not work when using GNU screen. To send Ctrl-Q to the QMX, you need to type Ctrl-a and then q. Second, to close a screen window, usually after selecting the 'Exit terminal' command in the QMX menus, type Ctrl-a and then k. This will prompt you with 'Really kill this window [y/n]', so type y. If you are already running screen, perhaps with multiple windows, you can also open a new window to connect to the QMX by typing Ctrl-a and then typing ':screen /dev/ttyACM0' (without the quotes) and pressing <Enter>. Once you type the colon (:), it and the remainder of this command will appear in the lower left corner of the window until you press<Enter>. When you are done, typing Ctrl-a and then k will close this window but not any other screen windows that you have created. Hopefully some of you will find these notes useful. Using the QMX terminal is even more important now with the changes in the new SSB beta firmware. Peter LaRue AI7YN

After the great BS170 meltdown on my QMX, I'm down to replacing Q507 (Q503 and the BS170's have been replaced and look good). I do not have a hot air rework station - only ChipQuik. It looks like the drain is a pad, not directly accessible with a soldering iron. Suggestions on how to replace Q507 with the materials I have ? 73, Steve, N2IC

Just finished QMX build and I can’t get my Mac to recognize the USB so as to upload firmware. I am powering with a 7v power supply. I am using USB c to usbA and then an adapter. Have tried two other cables with no success. I have seen all the tips on YouTube and also page 63 in the manual. Feel like I’ve wasted $150 on this radio and likely never to get it to work. I will try on a Windows machine if I can borrow one this week. Other than that don’t know what to do. Bill, KJ5IVB

Hi QMXies. As a sota enthusiast i was missing a working clock (on the QMX .. not QMX+) regardless if batteries have been removed before. There is everything there also in QMX, but the 32kHz Q and the buffer battery. I (carefully) released pins 6, 8, 9 of the STM32 from the PCB, soldered 3 thin wires to the elevated pins ant fixed them with epoxy glue. Then attached a 32kHz Q to 8 & 9 pin wires. As i don't need the PTT output for sota, i removed the PTT connector, which made room for the CR2016, attached to pin 6 wire. Settings "real time clock" set to QMX+ RTC and "set time" -- voi la. Now the RTC keeps on running while QMX is in his transport box without any power attached :-) I have to confess, you need some skills in working with very small soldering tips under the microscope, as the pins of the STM32 are really close together. Solder bridges don't have to bring you out of concept ;-) :-) Wolfgang OE3WHU

My assembled QMX+ arrived from QRP Labs on Monday 24 March and today I have a problem. I powered the rig on and keyed my paddles, but heard only one dit before an 'S' displayed on the screen (high SWR). The antenna is resonant (see below) so I powered off the QMX+. Powering on again, I heard static briefly in my headphones but the display would not light up. I tried a couple more times to power on, with same result. Two days ago I connected an EF-15 end-fed tuned dipole via 15m of Mini8 coax to the QMX+ and was calling CQ. I got no response but I saw on the RBN that my signal was picked up in Vermont with 9dB snr--from Ireland. So I know the antenna is OK and I'm using the same setup today. I know the power to the QMX+ is OK--it is using a battery that today reads 11.8V output on my WattsUp in-line power meter. My problem seems similar to the string /g/QRPLabs/topic/qmx_failure_power/108778736 but it shows no resolution to that problem. I'm not technical and wouldn't trust myself to measure components, etc--and this is a brand-new QMX+ assembled and tested in Turkey. Would anyone have suggestions what to do next? Many thanks in advance for any ideas, Tim Ei2KA

On p25 of the Rev 3 QMX+ manual, there is a check for continuity to ground from three points A. BEFORE installing T501, when checking the three points A, I get about 15 ohms with the DMM black lead on the ground connection, but open circuit (desired) with the leads reversed (ie red lead on the ground connection). Is this to be expected? The 4 BS170's ARE installed. I am troubleshooting a continuity check problem identified after having installed T501 (now removed). Thanks Steve AK0M

A couple of weeks ago, I think, I brought up an issue I'd seen with my QMX low-band (20-80), where I was only getting about 1.2W out on 20 meters. Today, I decided to run some tests using a new power meter and dummy load, and also to see if maybe I'd set a setting wrong. The results were a little surprising, and probably point to some hardware fault, and not a setting problem. To double-check that theory, I did a factory reset and a firmware upgrade, and received the same results. I have both narrated video of the power meter, and screen recordings of the terminal app, that I can edit together if they would be useful. I had been thinking of terms of posting a YouTube video about "fixing it" but then, of course, I was not able to fix it! (That said, I may at some point do a YouTube video guided tour of the Terminal App!) What I'm seeing when I hit the 'T' key in the Diagnostics screen: Input voltage looks steady at 11.7 SMPS 3.3V shows 3.3V, 5V shows 5V, Bias SMPS shows 30mA as does PIN Bias For all of these -- and this may be the hint -- the transmitter voltage shows 10.2 transmitting, 0.6 idle 80m: Diagnostics show 4.7W, power meter shows 2.0 60m: Diagnostics show 5W, power meter shows 3 40m: Diagnostics show 4.3W, power meter shows 2.5 30m: Diagnostics show 2.5W, power meter shows 1.25 20m: Diagnostics show 1.2-1.3W, power meter shows 0.5 Where is the most likely place to look for both the shortfall relative to the meter, and the shortfall relative to general expectations of 5W as opposed to 1.2? Thanks! Michael WD0OM

AIUI adding the GPS to the QMX+ will allow the PPS signal from the GPS to calibrate the TXCO. This seems mostly be for the beacon modes but does the calibration apply for normal operation as well? And how can you tell? Does the System Configuration - TCXO frequency setting get updated? Hope that makes sense. Chris, G5CTH

Does anyone have an easy safe method of dimming the backlight on the QMX+ Perhaps changing/adding a resistor. The bright backlight is fine in a well let room or outdoors but in my dimly lit bat/ham cave it’s hard on the eyes. Thanks, Dave

On Mon, Jan 13, 2025 at 03:55 PM, Damon wrote: The new PA’s were placed and I powered up again with 12v and current limited to 250mA. On the display, I have a blinking “6” low voltage alarm. Damon, blinking "6" only in TX mode or also in RX mode before try to TX or after try to TX? For TX mode 250 mA is much to low and the power supply will hit the limit. When the power supply is going below 6 V the QMX is disabling the PA, the current is below 250 mA again and the voltage comes up to the value from before. (Such a fast down and up of the supply voltage is dangerous for the QMX.) 12V rail at 6.68Vdc How much external voltage? 6.68 V in which mode (TX, RX)? Good VFO clock output from CLK0 & CLK1 into IC503. I guess you mean IC403. Good and expected values shown from IC’s 501-503. Like described in QMX QMX_plus PA problems, broken BS170? With or without BS170? PA’s dropping 980mV as measured at T501. Dropping in which way? 980 mV DC or AC rms or AC pp or what? Measured at which point of T501. What is your oscilloscope showing at the drains of the BS170 (AC and DC, RX mode and TX mode)? 73 Ludwig