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Hi everyone, I started assembling my Rev4 QDX kit last night that I've been sitting on for years. I got to the step of installing T1, and it seemed to go alright, but when I went to check the continuity as described in the instructions, I found problems. I have good continuity between the ends and center tap of the primary winding and also the ends of the secondary winding. There is no continuity between any of the parts of the primary winding and the secondary winding. There is good continuity between all of the "A" points, and no continuity between any of the "A" and "B" points. However, I am not getting any continuity between the two "B" points. I do get continuity between the ground plane through hole point "B" and the capacitor C17 adjacent to C34 (the other "B" point). I tried removing the transformer, re scraping the wire ends and re soldering it, but it still has the same issue. Any suggestions?? Thanks, Nate KV4RD *** Nathaniel Drexler

The clock on my QMXplus seems to drift many minutes every day. When I do an operating session or a POTA activation I will need to remember to set the clock when I sit down and power it up. I set the time to UTC to make paper logging easier. I have a new quality CR2032 battery in my QMXplus in case you wondered. i haven’t yet measured the clock drift, but was surprised it was significant. I think a number of contacts I uploaded to LoTW had no QSL because my estimate of the correct time was wrong. (A day or two later I discovered the time was way off before I uploaded, and changed the times in my electronic log to my estimated corrected time) Or I could get the OLG3 GNSS module which I think will set the QMXplus time, but that requires another component and setup to my portable kit. I probably won’t bother but keep thinking about other solutions. My Home QTH transceivers are spot on the correct UTC time. I can take a PC or IPad and do my logging on it. Another component to take. Q: Before I decide what to do, How much does your QMXplus clock drift?

I am having difficulties with ALL my USB soundcards, including the QMX+. My station computer is a Windows10 machine. All was working well and I have been playing with SSB recently. Today I decided to use FT8 and try my luck with ZS8M. When I opened JTDX I received the error "An error opening the audio input device has occurred." Interestingly I could transmit however there was no audio on the waterfall. Unsure of my dilemma I tried another rig and another external USB soundcard and again I had the same error. I have 3 USB soundcards (including the QMX+). One is a digital interface for my QRO rig the 2nd is for CW Skimmer and the 3rd is the QMX+. NONE of the USB cards can receive audio data? I have checked each audio device and they seem to be setup correctly and the sound icon on the taskbar is at full audio with the correct device shown. But no audio is received by any of the soundcards or their appropriate software. The ONLY fully working soundcard is the built-in card on my Win10 machine. I don't think that this is a QMX+ issue but much broader. (I am running firmware 1_001_003.) Has anyone encountered anything similar? Thanks, -- 73, Rick VE7TK Website: https://www.ve7tk.ca/

Got my QMX with version 9 of Beta firmware to work on SSTV this evening -- MMSSTV software, 12 volt build running at 9.5 volts, Mic = USB, Vox = ON, usual selections in MMSSTV. Solid contact with W2WTF in Flowery Branch, GA from Elizabethtown, PA. No over heating of radio. Bands are pretty rotten today, but thought I would give it a try!

WARNING!!! Running the SSB calibration in automatic mode has the potential to burn out the finals. I've read at least 1 other thread where running the SSB calibration resulted in failures in the output stage. I now have a non-working QMX+ because of this. I replaced the blown final, but there is still another problem in the transmit circuit. When I attempt to transmit from the diagnostics screen, I get 0 output power. If I put a scope on the gates of Q503-Q506, I see what I assume to be a good signal, it's at least at the right frequency. Q507 heats up when attempting to transmit. I also note that the duty cycle for the 5V SMPS jumps up to around 75%, I assume because it's trying to push out so much current. I'm kind of stuck here, I have the tools (meter, scope, rework station), but I'm sorely lacking in troubleshooting skills for this type of problem. This was my second QMX+ build, and I was ecstatic when it worked flawlessly on first power up. I made some contacts on it, and decided to get it ready to try SSB. Kicking myself for not reading more before diving in to the calibration or I might have not used the automatic option. I'm going to go read what I can find regarding an issue like this. If anyone can offer any troubleshooting tips they would be greatly appreciated. I'm looking for what to check, and what a reasonable result would be. It's built for 12 volts. Currently (pun unintended), the supply voltage drops to about 7 volts during transmit when I have the power supply current limit set to 700 mA. I checked and the unit seems to be able to sink as much current as I dare feed it. My first unit is on its way to Jeff. I'm going to work through this one myself, I hope. Thanks and 73. Andy WB9YXA

For those who wish to create/print their own QSL Card my GitHub repository might be of interest: https://github.com/sparks72/QSL-Card-Multilinqual-Editor 72/73 de Paul DJ0CU Feedback welcome.

Will QRP labs be at Hamvention in Ohio? If so, what booth/building please. Will you have built kits (QMX+) on hand for sale? Thanks and ‘73 Jim WX8J

Hans, I think calibration in _006 is better, but there are still some issues. I am attaching some screenshots from my QMX-lowband calibration that may help in diagnosing the phase-error cals that don't finish, and also a USB IMD optimization that was strange, and fixed itself when I repeated it. I did the initial calibration from a factory-reset condition, using the 'R' option to do all of the optimizations, which I then reviewed. The 80m Phase Error plot didn't complete - it stopped at about 700 on the x-axis. And retrying it with the 'O' repeated the same results. Then I retried a few more times and captured the attached 5 shots of the progression. Note that it for some reason started with a high DAC value, not the one corresponding to the x-axis, which is why it stopped early. Completely repeatable. The 20m USB IMD optimization looked crazy. The other IMDs looked OK. So I retried 20m using the 'O', and it cleaned itself up. See the initial and retry results in the last two attachments. I hope this is helpful- I will check the cal process/results on my other QMX*, and let you know if anything else interesting shows up. Stan KC7XE

We had 14 folks join the MI QRP Zoom Chat on 24 April. Please join us Thursday May 1 (and every Thursday) at 4PM Eastern for the Michigan QRP Club weekly QRP Chat where the main topics will be QRP and other ham interests. New hams are encouraged to participate and ask questions. It's fun, it's easy, and it's free. You only need a computer, a smart phone, or a tablet that can connect to the Internet. OR if you can't be close to any of those you can join by audio with any standard phone. Just follow the directions below. No software needs to be loaded or installed. Anyone can join and non members are welcome. Details are here: https://www.miqrp.net/zoom Zoom ID: 811 0835 6229 The topic for Thursday, 1 May will be an OPEN FORUM and maybe a who is going to Hamvention raise of hands. Ernie - NE3TE Harry - K9DXA Stan - WB8QJZ Pete - WK8S Bill - KU8H Tony - W8CDC Bill - N5IM (first time) Neil - N9NL Dave - N8SBE Yvon - AE7YD Cassie - KC9IH Kim - N8FNC John - M7FZC Jim - K8DDV (first time) I was not at the meeting so I have no notes to share. The agenda for the 1 May QRP Chat: Ernie to do a short introduction and acknowledge any new folks to the Zoom chat. The topic for next week will be an open forum. During the open forum anyone can take the floor. We will go one by one until all have had a chance to have the floor. Files, pictures and presentations can be shared if you have any. Please try to stay muted when someone has the floor. Thanks Ed AB8DF

Hi, has anybody tried the new firmware with VarAC and/or Winlink? Does it work?

Hi, I tried to use a standard Baofeng micro , the one with a small loudspeaker inside that is not usable with QMX. I have done the easy mods to make possible using this mike with the QMX. No a big issue ... Tried also the Microphone Test tool in the QMX sw, and the mike seems ok using only 40 db for gain. BUT, if I listen with another radio the modulation is very bad .. !! Possibly the two radio too close ?? Unfortunatly, if I talk ,does not seem to exit any RF or just a little bit, from the QMX ( I have a swr/wattmeter in line..). In CW all is ok, in SSB Baofeng micro seems no good. Have you tried the Baofeng Micro ? I guess every body owns one of this mike that why I am asking. 73 de angelo i1jck

Rig:- QMX+ rev 3, firmware 027:- I am getting WSPR reports of quite frequency drift (2-4) on 10m and 6m. I never got this with my QDX (always 0 drift reports). I wondered If anyone else is using PC driven WSPR mode on the QMX+ and if they are seeing the same problems? 73 ken g4apb

Hi all Just wanted to explain a few things about SSB calibration. Firstly, please understand that the calibration makes the performance excellent. Even without calibration the performance is quite respectable. Calibration is not a temporary thing that is only concerned with the beta firmware. It optimizes the transmission of SSB to your particular hardware setup (component tolerances, how you build the filters, etc). There are two kinds of calibration. The first is the phase pre-distortion calibration which measures the phase error in the QMX PA, so that it can build a calibration curve that can be used for compensation (pre-distortion). Phase error depends on amplitude. So if the system needs at a given instant to transmit, for example, 0.5 amplitude and 25-degrees of phase shift - then it will look at the stored calibration curve and see what the measured phase error was at 0.5 amplitude. Say 10 degrees. Then it can subtract 10 degrees from the desired 25, because it knows there will be 10 degrees of error, and command the '5351 to produce 15 degrees phase shift. That's the aim. The second calibration is of the necessary synchronization delay between phase and amplitude modulation. Since amplitude modulation takes effect in a short time after the new amplitude is commanded to the DAC, but phase modulation requires a frequency update to the '5351 which takes some time to communicate via the I2C serial bus to the '5351, it is necessary to delay the amplitude relative to the phase. There is also some fixed delay in the phase compensation which measures relative error, not absolute error (since we don't exactly know what the phase delay is through the receiver circuits). So the sync optimization tests to find the optimum delay of amplitude relative to phase modulation. Sync calibration is run separately for USB and LSB sidebands. Both of these types of calibration require operating the transmitter and receiver at the SAME time. The phase calibration increases the amplitude in steps, increasing the PA voltage up to 12V a step at a time. Each step transmits a steady carrier (CW) for just over one second. Even at full power this is only for one second so is expected to be much less stress on the transistors than an FT8 over would be (12.8 seconds). The synchronization calibration transmits two-tone (700 + 1900 Hz) at full PEP during the test, but SSB is a much lower average current anyway than CW so it should not be stressing the PA transistors. Therefore if people have been using FT8 normally, then report that PA transistors are blown during calibration, which operates the transmitter either at lower power or for shorter durations, then this is a mystery why that could happen. One possible explanation is that the PA amplitude modulator (transistor Q507 and its four support transistors) is not working properly. If the amplitude was always at maximum because Q507 is not modulating it, then indeed this would stress the transistors somewhat. This is why in the recent firmware updates last week, I added a check before the calibration starts, where the PA voltage is set somewhere halfway (set to 5V actually) and then measured there, and if it is not near to 5V we know there is a problem, you are warned, and the calibration does not proceed. There's also the new "PA mod. test" screen in the Hardware tests menu, which steps the amplitude modulation up and measures the result; this should always show a straight line from near zero to near supply voltage, like the attached AM.png. IF it does not, if it shows a straight line across the top of the screen, then you will know that your PA amplitude modulator isn't doing its job, and you need to fix that. The radio may appear to work normally in CW and Digi modes, and you'd never know, but actually it wouldn't be doing envelope shaping. And it can't work for SSB without the amplitude modulation. Regarding the calibration itself, as I mentioned the QMX is operating its transmitter and receiver at the same time. It transmits (CW for phase error, two-tone SSB for synchronization optimization)

Hey, I just assembled this a few days ago, made a couple of contacts with an end-fed. What I found odd is that when I attached a 50 ohm dummy load to the output and measured SWR, it was around 1.5 on 20m and <2 on other bands. Surely it shouldn't be that? What may have I done wrong? Should I worry? 73 de HF2J

Hey, I've just noticed that this cap (C526) on my Rev 4 QMX is chipped off a bit - can you either point me at the schematics or tell me what value it is? Thanks, J