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QMX Mid-band L401 Mux allocation?
I neglected to check enable lines while my radio was open. Does anyone happen to know which bands correspond to which IC402 inputs?
I know that 15/17/20 go to 0 or 1, and 30/40/60 go to 2 or 3. But in both cases that's three bands but only two inputs.
Sketch from the manual:
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Re: ABS for QMX+ v1.2 speaker issues
Stan,
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Thank you for taking the time to explain how to troubleshoot my speaker issue.? Following your instructions, I sampled pin(3) and pin(5) of the LM386 with my scope.? I don't have much experience using a scope, so this exercise was a good learning experience for me.
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I settled on setting the sidetone volume at 80 while using the speaker.? The volume is perfect with the case covers in place.? I set the sidetone volume at 50 when using my headphones.
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I am really enjoying the portability and flexibility having a QMX+ with an ATU, self-contained battery and speaker.
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Howard N8HO |
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Re: My new QMX+
#QMXplus
Stan,
Absolutely you can eliminate 6 m and put 20 m (or 15 m) by itself. I was more thinking Hans could add one more LPF space so you wouldn't have to eliminate a band. There certainly is PCB real estate to do that. However, I am not that worried about it. I am perfectly happy the way it is. A half (or less) S unit down is NBD. In fact, I often deliberately run my 12 V rigs at 9-10 V anyway.?
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73, Dan? NM3A |
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Re: Handheld QMX?
Hi Yoon,
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I really like your design!
It always makes me feel nervous to see a long antenna attached directly to the rig (imagining the stress on the circuit board).
The boot and hat arrangement could be made very strong and easy/cheap to repair/replace if it breaks.
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73, Mike KK7ER
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Re: My new QMX+
#QMXplus
T501 can be left as is, but I don't think we can use the primary center tap when going for CMCD.
Need two L502's to power the two sets of BS170 drains.
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From ?
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And this brings us to current-switching class D amplifiers. These actually?need?separate RF chokes that conduct a constant current over the RF cycle, and they?need?the drains?being completely decoupled from each other! So, using current-mode class D turns a very difficult design problem into a very easily implemented design feature!
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Jerry, KE7ER
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On Sat, Feb 22, 2025 at 10:33 AM, Jerry Gaffke wrote:
Could take the QMX+, redesign T501 and the LPF"s for CMCD with the tank placed out beyond T501. |
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Re: Any hope left for the repair of this ?
Hello Daniel,
cleaning the existent pads using flux and desolder braid should be easy. Than check if the yellow capacitors are well connected, solder if not. (C431 looks like desolderd.) The ripped pad is for pin 21 and regarding to the schematics not connected to anything. So this should be no problem. Solder a new IC and it should be ok (if no other problem exists).
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73 Ludwig
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Any hope left for the repair of this ?
Got the unit of someone who attempted to replace IC407 on their own. The board isn’t looking great. Just wanted the opinions of potential repair people better than myself
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the unit still turns on but of course gets stuck at initialising audio
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Daniel ZL2DTL/ZL4YOTA?
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Matti,
Very unfortunate problems you are having. The voltages you measured with the button pressed show that you have something shorting in your QMX+, on both the Vcc and Vdd lines.? It is not easy to say exactly what is shorted without further measurements, but most commonly there are issues with connections and solder flakes.? Or something external.??
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And if you shorted your Vdd to Vcc while probing, if you didn't have a current limit of 250mA or less set on your power supply, you likely blew one of the protection diodes, probably D109.?
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But it is not accurate nor fair to blame these issues on the QMX+ v2 or v3 SMPS design. Shorting without a fuse or current limit would damage some component in almost any design, yes, even with linear regulators.
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Perhaps QMX+ should have been designed with a 250mA fuse on the Vdd line, then assembly or handing issues that cause shorts would blow the fuse rather than the protection diode - then instead of placing blame on a power supply design,? ?we would be looking for what is shorting and fix it.
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Also note that a double long-press of the power button shouldn't have caused any issue.? I have done that before without consequences. Similar with a very long press, which first powers down then powers back up.
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Stan KC7XE? |
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Re: My new QMX+
#QMXplus
Could take the QMX+, redesign T501 and the LPF"s for CMCD with the tank placed out beyond T501.
It's preferable to have the tank right across the BS170 drains so T501 only needs to deal with the fundamental,?
but that makes band switching much more problematic.
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We have six LPF's in the QMX+.? Let's assume we shoot for a high enough Q that we need
to separate the CW and Phone parts of the 80m band.? So we might choose to peak those
six LPF slots (now resonant CMCD style output networks) for 80m, 75m, 40m, 20m 15m 10m.
That's all I could hope for in a $125 CW/Digital/SSB transceiver.
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It might be possible to still hit the WARC bands at reduced power.
Or you blow a second $125 for a QMX+ tuned to a few different bands.
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Jerry, KE7ER
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On Sat, Feb 22, 2025 at 09:27 AM, Stan Dye wrote:
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Re: Handheld QMX?
On Fri, Feb 21, 2025 at 08:01 AM, Steve Sutterer AK0M wrote:
Has anyone considered or even actually built an integrated handheld QMX rig? I am thinking something like the KH1. I can envision a 3D printed case that includes the QMX, small battery pack, and a manual Z-match or even automatic tuner that could be used with a whip or random wire antenna. Could include integrated touch paddles or paddles jack…Back to the original topic, I was also imagining something similar, docking like the attached sketch - though it is not a 3d printed case but an aluminum enclosure. It is still only imagination, as I can't find an enclosure that has the same width and depth as the QMX enclosure. Sadly I don't have a 3d printer nor any skill to create something out of it. ?
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73,
Yoon KM6KJI |
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Re: Handheld QMX?
I wholeheartedly agree.? I've designed three PCBs for antennas (two baluns and a T-match tuner) in kicad in the last few months.? Building and troubleshooting my QMX has brought me closer to buying my own oscilloscope, and I'm considering doing a run of kits using the affordable PCB assembly services now available to us all.? It is definitely a good time to be in the hobby :) |
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Re: Handheld QMX?
This is the golden age of electronic experimentation.
I can design a PCB in Kicad and have 5 boards built and delivered in a week or two for $5.
Parts for a complete transceiver similar to the Micro-mountaineer can be found online?
for a grand total of maybe $10, along with all the needed datasheets.
A $15 RPi-Zero would run circles around a million dollar Cray 1 for DSP algorithms.
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Communications is no longer problematic in an era of cell phones and email, radio isn't quite so magical.
Many of the experimenters have moved on to DIY audio, electric vehicles, robotics, off-grid power.?
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The big thing in RF power amps these days is Current Mode Class D, or CMCD.
This is considered a further development beyond Class E or Class F, and the subject of numerous MS and PHd theses.
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Curiously enough, it's the AM phone crowd doing much of the experimentation with DIY builds in ham radio.
A CMCD type RF amp with a Class D AM modulator could be easily adapted for use with Hans' Synthesized EER scheme.
The INN650D02's mentioned by KJ7AGO in that final web link above are $1 on Aliexpress, I've got 20 getting shipped this way.
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Around 1970, an aging ham gifted me with his junk box.
Included some Ford coils with which to build a spark gap transmitter.
(Scary to think that he was younger than I am now.)
Also a 2kv 2kW plate transformer and a couple dozen 810 triodes.
Still have the 810's down in the basement, and occasionally consider building this push-pull amp:
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Curiously, that 810 design from 1938 has the topology of a Current Mode Class D amplifier.
There are published examples of that design dating back to about 1930.
This 1934 guide for amateurs has many different CMCD style designs.
Those guys knew what worked, and I'm sure they fiddled with drive levels and? tank circuit C,L values
till they got maximum efficiency.? ?Which would put it in CMCD mode with ZVS.
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Jerry, KE7ER
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On Sat, Feb 22, 2025 at 07:38 AM, bill K7WXW wrote:
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Re: No special characters to delete messages?
Chris, reading the firmware release notes, I see that message editing from the menu was broken in firmware versions 24 and 25, and is fixed in the current version. So you will need to update firmware, or edit the messages using the terminal program.
Stan KC7XE? |
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Re: My new QMX+
#QMXplus
On Sat, Feb 22, 2025 at 09:12 AM, Mark Flavin wrote:
You can do this yourself by disabling the unwanted bands in the band configuration screen, then modify the filters and filter selections to be specific to the bands you want. |
va3rr
Daniel ZL2DTL
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