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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

I just finished my QMX+ and thought I would share my RF power out readings. I did my best to wind all the torroids evenly though not perfect. Measurements are made with an Oak Hills QRP meter into 50 ohms, and with a LiPo supply voltage of 13.4 volts through a single diode. Voltage at the rig when keyed is just below 12 volts. 73, Gary W8PU 160 m - 5.9 w 80 m - 5 w 60 m - 3.9 w 40 m - 3.9 w 30 m - 3.7 w 20 m - 3 w 17 m - 2.3 w 15 m - 4 w 12 m - 2 w 10 m - 3 w 6 m - 2 w

Hi all, I’ve completed assembly of my 60–15m QMX. It powers on and passes the RF and SWR sweep tests. Test ADC I/Q shows sine waves, particularly on 60m. I can hear what sounds like FT8 on 7.074 MHz in DIGI mode, and the tones appear to cycle every 15 seconds as expected. However, I’ve noticed that disconnecting the antenna makes little or no audible difference — there’s no significant drop in the noise floor or change in the signal. Additional observations: The BNC center pin shows ~0 Ω to ground (I understand this is expected due to the SWR bridge). BNC center has continuity to one side of C510 and C526. Test ADC I/Q and scope work as expected. Reflowed L506, L508, L510, L511, L512, and L513 for better LPF continuity. I’ve confirmed IC402 pin 13 is not grounded, but I don’t have continuity from the BNC center to pin 13. At this point, I’m hearing what I believe is live FT8, but the lack of change when removing the antenna is making me question whether the antenna signal is actually routed through the intended receive path. Would appreciate any guidance or suggestions for what else to check. Thanks! -Tanner

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

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

Could someone please explain to me a simple, quick, non-fiddly way to send a signal that my T-1 tuner can use to tune itself? I tried searching the forums but didn't find anything. Thanks all.

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?

Based on recommendations on here, I sent my dead QMX to Jeff Moore disassembled in a sandwich bag. It is now back home after he found multiple issues with it (factory assembled). All is working as should. I just finished building a qrpguys microphone to use with it and made 3 ssb pota contacts. This without doing any calibration, just the stock configuration. Thanks Jeff for a great repair!!! Ken/NO4D

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