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Hi everyone. With the release of the SSB firmware out of beta, I thought I would make my offer to source K6ARKs wonderful little microphones, which can be found here: https://www.printables.com/model/320559-mini-microphone-for-qmx-trusdx-usdx-kx2-and-kx3, one more time. Adam (K6ARK) made a super fantastic little miniature mic case, and they work with the QMX quite nicely. I print the cases in PLA, and have the following colors available: Black, White, Grey, Navy Blue, Orange, Light Green, Red, Gold, Purple, Sand Stone, Light Blue Stone, Turquoise stone, and Marble Stone (The stone colors look like marble or granite - little flecks of darker color in them - The marble one winds up looking like bleached bone). The kit includes: 3D Printed case in PLA 3.5mm jack Electret Mic Element Microswitch for PTT For each mic, $10 for kit, $15 fully assembled and tested. This price includes shipping in the US. I am happy to make you more than one, some people want one for home and one for the go bag, that's great. You will need to provide your own AUX cable (3.5mm male to male) to go between the mic and the radio. I have had several ask what cord I am using, So I have included this link to one I am using and that I test all my assembled mics with; it seems to work quite well: https://a.co/d/36GDDXf (This is a shortened, non-affiliated link to Amazon.com page for the cable I use) If you are interested, send me a private email, and I will send you payment details. My email address is good on QRZ.

Everything has gone textbook right for my QMX+ (kit built) for a few weeks now, but I knew it couldn't last. I was receiving with the USB connected to a Raspberry Pi 4 running WSJT-x and it seemed to be working fine. Then I looked back and the display was dark. Pushing the startup knob drops the regulated voltage to 11v and current limit of 600+mA, which goes back to zero mA when the push knob is released. No idea what happened, but it's down to the basement "bench" to take a look. Film at 11..... -- Brent DeWitt, AB1LF Milford, MA

The wiki page QMX QMX_plus Debugging has been updated by @Ludwig_DH8WN <DH8WN@...>. Compare Revisions

Greetings to the brain trust. I have a kit built QMX which is awesome and works great on CW. I have upgraded to the 1.02.000 ( the latest firmware) and added a QRP GUYS mic. Everything seems to check out in the hardware tests, but it seems very low output on SSB. I've set the mic. gain to 75 which seems to help, some. Any ideas on trouble shooting? Thanks in advance. WX7J Doug

Thank you Eric. Got mine this week and transmitted SSB for the first time after 45 years off the air. Great mic at a terrific price. Now back to my regularly scheduled CW practice. 72 WB0ZJJ South Florida

Enjoy https://www.youtube.com/watch?v=bsDBcFXgHbY 73 DE muhsin TA1MHS

The radio is a Ver. 1 QMX plus that in general performs exactly like I expect. It does not have the GPS option installed, and there is no battery in the clock battery slot. The radio is used for CW only. As the title suggests, I have an approximate 1000 tone on only 12M and 6M bands. It is internal, in that I can remove antenna and it's still there. It does not change in level or tone while tuning around the band. It appears to de-sense the receiver a bit, as a signal must be pretty strong for me to be able to copy it on 12M. There is normally a 'beat' frequency between the received signal and the tone when I can copy someone. I have run the I/Q sweeps in Putty, using a raspberry pi computer. The tone is present with or without the computer attached. The I/Q sweeps look very nice on the lower bands, and begin to deteriorate as the frequency goes up. They are still showing the two sine waves, but are a bit distorted( not a perfect line of x's ). This deterioration is also noted on 10M and 15M ( to some extent ) and the sweeps for 12M and 6M are not suspiciously worse than others. 10M works flawlessly, as do the other bands. The remaining filter sweeps look good, with some tweaking needed possibly, but totally functional as is. I have a set of QMX HB and LB radios to compare symptoms, and the HB QMX does not have the 'tone' on 12M when swapped into the system. I am curious what path to take troubleshooting this issue. I did not find anything in the archives that addressed this strange behavior. Thanks & 73 Dick W4PID

Hi, I’ve had my QMX+ for a number of months and had tested the then beta now regular SSB firmware with good results except pretty low output power in SSB. As I had never gotten around to fine tune the LPFs when building it I decided this was the logical next thing. So I fiddled with spreading and compressing turns on the toroids and managed to get all bands to between 4 and 5w output for CW except 160m that was already at 6w. Running 12.0v input and build for 12v Being happy with results I then first tested resetting to factory defaults, and then tested SSB output power. Still max 2-2.5w according to the Bird. I then decided to run the SSB calibration again. Worked fine til perhaps 12m or 10m phase. I then heard some terrible noise from the speaker and saw the QMX crashing with all blocks in the display and turning itself off. I tried powering on again, but won’t start now. Just blank display and current protection on PSU kicks in due to over current. I suspect maybe finals are fried with internal short as result? Jonas 7 maj 2025 kl. 23:12 skrev Stan Dye via groups.io <standye@...>: ? On Wed, May 7, 2025 at 01:38 PM, Wiggle Pig wrote: It’s D503 and D504 These are placeholders for diodes that could be placed across the BS170 outputs, as was commonly done with QDX. Hans included them in the design, but has not encouraged installing the diodes, which he believes are unnecessary for QMX. They may suppress spikes, but they also add additional capacitance to the PA, which may affect it adversely in other ways. There were many posts on this list regarding this topic a year or so ago. Stan KC7XE

Checking my newly built 20M band QCX+ I found the following facts: On a 50 Ohm dummy load - with a 13.5V DC supply I only get around 3 Watt output; - 8.7 Peak BPF looks OK; - 8.8 I-Q Bal 8.9 Phase Lo and 8.10 Phase Hi show high minimum values; After connecting my AlexLoop magnetic antenna I get only noise where I should ear some CW and around 14,074 some FT8 noise. I went to 15,000 MHz to ear the hour signal but nothing except a continuous signal on 15,005MHz. Para 7.3 page 130 of the manual writes: "Your results may vary depending on your Low Pass Filter inductor construction! If the cut-off frequency becomes too low, then you start to get attenuation at the operating frequency. In this case you can remove one turn or two from each toroid." As the LPF work both in Rx and TX I understand that if their cut-off frequency is too low I loose Rx sensitivity and TX output power. Do you think I should actually start by removing one turn on L1, L2 and L3? I guess it would just raise a little the cut-off frequency without increasing the 2nd and 3rd harmonics? 73 - Pierre - FK8IH

I have been trying several times to update my QMX plus to the newest firmware without success. The computer does not recognize the QMX plus. Just for giggles I updated both my QMX’s Without any issue. I plugged them in like normal and they showed up as the thumb drive. What am I doing wrong? I’ve searched this topic and cannot find anything. Appreciate all the help. -- Trevor (N0YMA)

Starting a new thread. Scouring the web, here's mention by KG7AGO of using a GaN-FET similar to the INN650D240A getting 300 W on 20 meters with a 60v supply. https://www.qrz.com/db/KJ7AGO https://amfone.net/Amforum/index.php?topic=47457.0 (search for KG7AGO) The amp would be more efficient at a higher supply voltage, but to keep heat down we'd need a higher turns ratio on the output transformer. Not only does the higher voltage reduce resistive losses due to the internal Rds, it drastically reduces internal capacitances. These parts are rated for a Vds_max of 650v A power out from a 100% efficient current mode class D power amp is given by this paper https://repositorio.inesctec.pt/server/api/core/bitstreams/4b52de91-5d27-41cc-acc2-70feeca9a7c7/content His equation for power out resolves to this python script: def pout(Vdd, R): return(3.1416**2 * Vdd**2 / (2 * R)) Also, the peak voltage for a current mode class D amp is pi times the DC supply voltage when properly loaded. I have figured out where that math comes from, would be happy to explain if anyone is curious. Trying that formula out for 50 Volts DC into 50 Ohms (a 1:1 turns ratio) we get: pout(50, 50) # 246.7 Watts We get the same 246.7 Watts with 100v into 200 ohms (a 2:1 turns ratio, peak Vds of 314v) 150v into 450 ohms (a 3:1 turns ratio, peak Vds of 471v) 200v into 800 ohms (a 4:1 turns ratio, peak Vds of 628v) Power out is proportional to the square of the DC supply voltage, for a given turns ratio we can reduce heat by reducing the DC supply voltage: 100v into 800 ohms gives 61.7 Watts, or 1/4 the power at 200v From the datasheet for that $0.04 GaN-FET (on JCLPCB website) https://www.innoscience.com/uploads/61af2c81/INN650D240A_Datasheet_V1.0.pdf it claims to be able to dissipate 75 Watts into a 25C heatsink. As Allison notes, the package is not easy to attach to a heatsink. I think we could have JCLPCB solder it down to a small multilayer board with lots of thick copper planes and lots of vias, then bolting that board to a heatsink. Should dissipate maybe 20 Watts, good enough for a 100W amp. Make those boards available for $5 or less. If the Gan-FET's fail, replace the board. Jerry, KE7ER ######################################################### I hijacked this other thread with talk of GAN FET's for an RF amp /g/QRPLabs/topic/113293149#msg146121 On Sun, May 25, 2025 at 04:44 PM, ajparent1/kb1gmx wrote: I've worked with GAN mosFets and that was 10 years ago. The ones I used easily ran at 15mhz very high speed 20W switcher. The TI driver chip was the real limiter. The GAN devices were froom EPC. And yes they can make very efficient amplifiers. They are optimized for switching and with very low RDSon and fast switching speeds they don't get very warm. Never tried them in a linear class A or B format. Cooling a beamlead chip 120x40x 60 mils would be a mounting challenge for most. One would hope for a flavor of a flange package. On Sun, May 25, 2025 at 03:51 PM, Jerry Gaffke wrote: Anyways, I was hoping you might ask some questions about that $0.04 GanFET in the other thread. Near as I can tell, two of those should make a dandy legal limit amp. Probably fine at 4mhz, but cooling those suckers at 30mhz might be an issue. /g/QRPLabs/message/146094 It all started with this post in yet another thread: /g/QRPLabs/message/146094 On Sun, May 25, 2025 at 09:09 AM, Jerry Gaffke wrote: Moderately high power RF parts for linear amps don't have much of a market, they come and go. The MRF101 and MRF300 seem to be the primary choices these days, who knows how long they will be available. For decades the low end amateur gear has been using the IRF510 to achieve moderately high power, occasionally with a half dozen of them in parallel. But the IRF510 is not designed to be linear and also requires a fair bit of gate drive, making a linear RF amp a difficult challenge. Polar modulation should ease this situation. I've been looking at some of the GanFET's. These can be high powered devices with very low internal capacitances. The

A new chat has been created: Not sure where to ask this, so will try here: My wife purchased a 40m QCX-Mini kit in the fall/winter of 2023 as a Christmas Gift. She ordered as a guest and got rid of emails related to the purchase, so I don't think I have a way to get the order number. Is it possible to lookup the order/serial number based on an email address and/or a delivery address? I have an itch to laser engrave my enclosure with the S/N, band, and options (TCXO and AGC). This is the main reason I'm interested in recovering the S/N. Thanks! Ben (KF0KXW) By: balexander87@... View/Join This Chat Do not reply to this message to post to the chat. You can participate in chats only through the group's website.

I've successfully have built many kits, but I always wondered.... I push the thru-the-the board component leads from the top of the board thru to the bottom of the board. I've always wondered, for thru-the-board components, should I solder the component thru lead and pad on the bottom of the board, or should I solder both sides of the component lead (top and bottom of the board)? And if I only solder the component thru lead and pad, should I see solder flow on the top side of the board/lead? Thanks, Roy de K2RMA

Anybody know what those two shiny blobs between R205 and R208 and Q204 and R210 are for? They show up on page 2 of the schematics as JP202 and JP204. Thanks.

My QMX+, a factory 12v build, draws 160ma at 9.28v, the voltage at which I operate for tx/rx. for all modes. Transmit current is consistent with my readings. The various PDF manuals I have searched, speak of ~80ma for rx. I am interested to know if mine is a typical, and how it compares to other build and operating voltages between 9v and 12v TIA, Pete/wa4hei

Hello everyone. My name is Jesus. I recently purchased a QMX multi-band multi-mode transceiver with the 80/60/40/30/20 version. I assembled the radio and made sure to perform checks to ensure there was no shorts to ground. I proceeded to power up the radio and the radio did not power up. There was no power consumption. A quick inspection showed the D103 on one of the SMPS boards was sheared off possibly during shipping, maybe on assembly? Regardless I ordered 2 sets just to be safe. I installed the new set of SMPS and attempted to power the QMX on again. The transceiver still does not show signs of life. No power consumption showed on the meter. I did some checks with my limited knowledge. Power seems to be getting to the SMPS. Ground is in tact. There is no 3v or 5v output from the SMPS. The board does not power on or register as a device via my PC. I wanted to reach out for some guidance on any additional checks I can perform? I double checked all the solder joints with a microscope and can’t see any bridging that could short anything out. So I’m suspecting there’s an open somewhere I’m not seeing.

13:00 session only Jorma OH8TX remembered the date without announcement. Lets hope others will have time for 19:00 Martin DK3UW

What's the short story on why the onboard QMX+ microphone doesn't work (yet). Is there an upcoming solution? Just curious, Roy de K2RMA

I have run my U3S many times before and it has run flawlessly with either a Beitian E-280 or Acxico GPS module attached. Both are U-blox M8 series. It has been sitting for some time, but I have a new propagation test and pulled it out to set it up again. The unit has the 25MHz TCXO module installed. The heart pumps on the screen, and the Time display is dead on when watching WSJT-X on my computer or a GPS clock screen from a GPS connected to the computer. Now it is acting rather strange. The old setup was 2-minutes WSPR TX, 2 minutes WSPR RX on each of 5 bands (10, 12, 15, 18, and 20m) with a Frame 30, so time between. The first TX decodes in WSJT, but each TX after that is late (later with each TX). By the 3rd TX (15m) it starts 10 seconds late and is not decoded at all. After each CAL sequence the display shows '=' and makes no changes. CAL (Step Time) is 01 100. I removed the RX windows and cut it to the 3 main bands (10m, 15m, and 20m) and the Frame to 10. Short_Setup.txt attached. The first TX decodes in WSJT, but each TX after that is late (later with each TX). The second TX (15m now) doesn't decode, and the 3rd TX (20m) starts 10 seconds late. Round it goes, and the first TX is right on time again! ------- Robert Giuliano KB8RCO

Hello, I am hoping I could get some assistance. I am currently building a QMX. I just installed the SWR bridge and I have continuity between all the connections. Is this correct or was it only supposed to have continuity between the wire pairs?