Re: QMX died before i got a chance to transmit.
All communications to Hans regarding specific orders/problems need to be done via the support system at qrp-labs.com, if I understand correctly.
No, the QMX definitely should not have failed after a short time of just listening - the exception being if the voltage on your power supply was way too high, e.g. 14V instead of 12V.? (Some fully charged so-called 12V batteries are really 14.4V or 13.8V - these should not be used with QMX without a voltage reducing circuit of some sort.)
But there are also possible 'infant mortality' parts failures that just happen - such failures are reasonably rare, but they do happen.
Please see the reply I made to your other post for some measurements to take.
Stan KC7XE
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Re: New QMX died while listening
Wow, that's bad luck.
The measurement of the antenna/ground is as expected - it is a DC short, but RF passes fine.
The measurements I would take first are some voltage and current measurements.? The current measurements are particularly instructive:
1) Power supply voltage.? If you can vary the voltage, set it to about 7.5V for the remainder of the measurements.? If you can set a current limit, set it to 250mA.? This will avoid any potential further damage.
2) Power supply current with QMX powered off
3) Power supply current while pressing power-on button
4) Power supply current after releasing power-on button
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Also read the 'startup' page on the Wiki so you know the sequence of events as power is first applied to QMX:? /g/QRPLabs/wiki/36878
All of the above data will help you communicate the details of the problem to Hans, and to you and us if you want to try and fix it yourself.
Stan KC7XE
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Re: QMX+ Pulse in headphones on TX
Thanks for having a look Stan and for the suggestions and recommendations.
Yes, noted the preinstalled caps.
I will certainly take a look at the suggested reading material and have another good look around.......
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Cheers
Ian ZL1HIM
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Re: QMX+ Pulse in headphones on TX
On Tue, May 20, 2025 at 08:11 PM, ZL1SGS wrote:
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Re: Two SMD component questions regarding a QMX+
The coil is fine as-is.? The chipped top does not affect functionality.
If the diode is working, there is no need to change it.? But it is a common 1N4148, so easy to find and replace if needed.
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Re: QMX+ Pulse in headphones on TX
Ok, you certainly have some sort of issue with the bias current supply.
It should be a very constant 30mA.
This could definitely cause a pulsing on tx as it wildly changes values.
All of the other info looks good.
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I am not an expert on this circuit, but know that a few others have had issues with it.
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I also remember reading from Jeff W1NC that failures in C504 are not uncommon (soldering, sometimes cracked, etc.)
One user had a broken L501.? And then the broken transistors noted at the above link.
So inspect that part of the circuitry carefully under high magnification for soldering issues or damaged parts.
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Good luck in quickly finding the issue...
Stan KC7XE
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p.s. rev 3 boards are the most recent; they have the LPF capacitors preinstalled.
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Re: QMX+ Pulse in headphones on TX
Have a look at this thread re bias current fluctuation: ?/g/QRPLabs/topic/107821803#msg127488
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a) no the direction doesn't matter, but I always do mine symmetrically
b) I use my finger to press the winding around the ends of the core, bending it so the wire sits right up against the ferrite
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Does the winding direction/handedness in each side of the T507 binocular core transformer have to be the same.? Hans stated in his 2023 Evolution in Radio Design paper (pg 21) that:
"... Here we use a more compact method, a
binocular core. The two transformers are each wound in the two
separate holes. As far as the binocular core is concerned, what happens
on one side is electrically invisible from what happens on the other. So
the use of a single binocular core instead of two toroids is a parts count
reduction benefit and also in our case, crucially, helps reduce the space
required, which in QMX Is at a premium."
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I've wound one side (10 turns) and started the second but I think I've reversed the direction and want to know if I have to start it over.
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BTW if there is a trick to getting these windings tight and neat I haven't figured it out.? My other torroids turned out OK looking but this one is not behaving.? Probably does not matter but I would prefer it look pretty (pilot's axiom - "If it looks right it will fly right").
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Re: QMX+ Pulse in headphones on TX
I note that the Bias current fluctuates wildly from -11mA to 62mA
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Re: QMX+ Pulse in headphones on TX
Thanks for replying Stan.
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1) Tried adjusting the keyed speed. Pulse remained the same. I had the same thought re cw mode as I got caught with that on the QMX.
2) The pulsing remains without any connection to the mic/paddle. Tune SWR transmit pulse is audible and also pulses the led on my zm-2
3) Revision 3 I believe. It was only later I noticed the note regarding the modification. I could only find version 3 printed on my board and being a recent purchase, fell outside that of the boards needing modification. The underside of my board looked nothing like that shown in the mod.
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I have attached images. I'm not used to the group io thing so please let me know if I have added them correctly.
Hope they help....
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Thanks again
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I had a CW practice session on May
20. I worked three stations.
Conditions were poor with high noise. I started on 40
meters. I switched to 20 meters but that was not any better.
SSN=66, SFI=119, A=13, K=2
My next CW practice session will be next week. I will
send out an announcement latter Anyone and everyone is
welcome. These practice sessions are? intended for operators
who are new to CW or they need some practice. IT DOES NOT
MATTER HOW POOR YOUR CW IS. Mistakes are OK. Poor fists are
OK. Slow speed is OK. Really slow speed is OK. This practice
is meant for you to improve your CW. I will do my best to
adjust to your skill level. Operate at any power level. If
several stations show up, I will operate as a round-table
control station. I will do it as a round-table so everyone
gets a chance to transmit. Please listen to my directions.
Details:
Date - TBD
Time - TBD
Band
- TBD
How to find me - I will find a clear frequency and call
CQ. Go to the Reverse Beacon Network and search for my
call sign AB8DF.
That will tell you what
frequency I am on. Tune your station to that frequency
and if you hear me give me a call. If there is a QSO in
progress, please wait for a break in the action. Then
send your callsign. If I hear you, I will invite you to
join the QSO and start a round-table QSO.
Reply to this email if you have questions.
IT DOES NOT MATTER HOW POOR CW IS
Ed
AB8DF_._,_._,_
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Re: QMX Feature Request - On Board CAT/serial monitor tool
Hello Matt
I can implement that yes. No problem. I'll add it to my list.?
QMX has 1, 2 or 3 Virtual COM Serial ports according to how you configure it in the System configurarion menu.?
Currently no UART interface is available on the QMX. I will also enable that soon, so it can function as a terminal or CAT interface.?
Generally with a USB Virtual COM Serial port, or a UART port, these are one-to-one connections. You can't (and shouldn't try) to get multiple hosts or devices connected. It won't work. But anyway you shouldn't need to do this since QMX already supports multiple USB Virtual COM ports and soon also UART.?
The way the serial ports on QMX work is that by default they are operating as a CAT interface. To change to terminal mode you press the return key which sends a carriage return (ASCII 13) character to QMX. Then it knows you want the terminal, since no CAT commands ever contain a carriage return character. If you want the port to go back to CAT mode you choose the "Exit" option from the top-level menu. Or power cycle.
73 Hans G0UPL
What it does: use the LCD to display characters received on the CAT serial port and characters transmitted over the serial port.
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The RX data could appear on the top line and the TX data on the bottom line. Perhaps an indicator of some sort that shows that data is being received by the QMX. even if the data can't be decoded as printable ascii characters. Perhaps, when the CAT/serial monitor is active then disable the terminal applications mode so that a newline character on the serial port doesn't take over the port for terminal applications.
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Why? I've been developing? microcontroller code to read VFO A on the QMX and display frequency and band info on a remote LCD. I first wrote a QMX CAT simulator program so that I could test and debug the microcontroller code easily. Also I have verified with PuTTY that the QMX responds correctly to incoming CAT commands. When I connect the microcontroller via USB to the QMX I am unable to establish that the two are communicating. This CAT/serial monitor diagnostic tool would help me answer the questions:
- Is the QMX receiving serial data on the CAT com port?
- What data CAT commands/data is received?
- What is being sent by the QMX over the com port.
This little rabbit hole opened up with this thread: /g/QRPLabs/topic/scripting_language/112779657 ?In which I suggest the OM use a microcontroller to speak CAT to the QMX. But then I asked myself if I could actually accomplish what I suggested and, here we are. I am aware of 8.7.3 CAT command test and 8.7.4? CAT monitor in the manual but it's not clear to me how to connect both a terminal and microcontroller to the QMX over the single USB-C port. It would be very helpful if the QMX itself could tell me on the LCD what is happening on the serial port. ?
Thanks and 73,
Matt
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Updated Wiki Page: QMX QMX_plus SSB Calibration and Predistortion
#wiki-notice
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Re: Dreaded dead transmit from SSB Calibration routine
The only things lost by not doing calibration are:
1) the phase pre-distortion compensation doesn't do anything (as if you had turned it off)
2) the sideband phase/amplitude synchronization is set to mid-level (50) for all bands, which on average is a reasonably good setting, vs. getting a custom value for each band.
Both of these are intended to decrease the IMD3 distortion products below its already reasonably good performance.
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All other SSB functionality is completely functional without calibration, including CESSB, compression, mic equalization, mic agc, mic noise gating, and amplitude pre-distortion compensation.
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Stan KC7XE
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Two SMD component questions regarding a QMX+
D505 has an odd appearance, it's missing the T4 label and appears damaged, but tests fine with a multimeter diode tester
The 331 SMD inductor in the second photo has a missing bit on the top. Should either of these be replaced?  
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New QMX died while listening
I received my fully assembled QMX about a week ago, but dont have a mic, or a cw key yet.? I got the high bands since I am a tech so i could use 10m now, and planning on getting my general in june/july.? so all i have done is listen a bit.? I was hoping to try digital modes with it sunday afternoon.? but sunday morning, i turned it on to listen again and about 5 minutes in i change a few bands and then i hear a sharp sound out of my speaker and the radio goes dead.? never to power on again.? double checked the power supply which was good.? even tried a second one and same thing, no power.? i took some multimeter readings while it was unplugged and power doesn't seem to be shorted to ground.? however measuring resistance between antenna and ground is very low resistance, like under 1 ohm.? i haven't opened it up yet as i haven't heard back from Hans.? not sure what next steps would be.
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Thanks for the help / direction.
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Ted
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Re: Dreaded dead transmit from SSB Calibration routine
Thank you, Stan.? I thought this might be the case.? ?Thankfully nothing seemed to have gone wrong from the calibration of my knock-around QMX.? Already had replaced the BS170s on that one last year after some tinkering went wrong.??
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What is lost in performance by not running the calibration routine, but still enabling CESSB, compression, and adjusting mic equalization???
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I am mainly a CW operator, but was curious about the CESSB mode, which has worked surprisingly well for me.? But just don't want to risk damaging my daily-driver QMX for something that I will rarely use.
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Re: QMX+ Pulse in headphones on TX
First the simple questions:
1) Are you sure you are not somehow stuck in CW mode, and hearing the pulses of 'dits' or 'dahs' from the keyer?? Maybe change the keyer speed and see if the pulsing also changes...
2) Does the pulsing stop if you remove the connector from the mic/paddle jack?? (and just do Tune SWR transmit)
2) Which hardware revision is your QMX+ kit, rev 1, 2, or 3?
3) Can you connect to a terminal emulator (PuTTY or TeraTerm) and bring up the terminal diagnostics?? You should be able to.? It would be helpful to see a screenshot of the diagnostics page both with 'T' pressed for transmit, and in receive mode.? Also running the PA mod test and LPF/SWR sweeps on a chosen band would likely provide useful info to track down the problem.
Stan KC7XE
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Re: New QMX+ Calibration victim
Jonas,
It is very uncommon for IC501/IC502 to fail, but quite common for IC503 to fail with blown finals.
So I would first lift a leg of IC503 that connects to the output of IC501 or IC502, and make sure it is not some failure in IC503 that causes the IC501/IC502 outputs to look bad.? Failures in ICs can affect their inputs as well as their outputs.
Stan KC7XE
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ZL1SGS
