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Let me start by saying there is no evidence that the situation I will describe is occurring or has ever occurred in a real QMX+. There is nothing here to worry about. It is most likely just something I am doing wrong so no panicking! OK, I have set up a model of the entire QMX+ lpf array. I have figured out how to make the diode model give a long reverse recovery (Vp parameter). The issue is not with recovery though. I am seeing something that is clear and yet must be wrong. The situation is that I have LPF4 enabled and the others disabled (by switching the gate of the correct BSS123). I set up my source to drive a signal big enough to generate 5 watts out, roughly 22 volts peak. I set up the sim to run without signal for 10 millisecnds to give the simulation time to stabilize the various voltages, mainly the time needed to charge all of the lpf shunt capacitors in the disabled filters up to 12-.7 volts. At that point I discovered that it is a bad idea to simply switch on the 22 volt peak input signal full blast because it ends up creating a large enough input to forward bias the unused filters input diodes. Once the diodes switch on, they cannot turn off until the input signal stops (28MHz period is way less that TRR of the diode). Switching on the lpf0-3 filters puts a near short on the PA output and kills any chance of the doubler getting the reverse bias up above 22 volts so it is fatal. OK, so maybe I need to "shape" the PA output. I "modulated" the input signal amplitude with an RC charge and here is where I ran into the issue. If you do the math on LPF0 capacitors (4400 pf total) charging through a 470k resistor, it takes 5 milliseconds or more to charge. What I found is that I had to use 5-6 milliseconds of "shaping" on the startup of the input signal in order to avoid tripping the LPF0. This seems too long to me but it looks like it is the way it is designed. Note that these diodes are OFF and get turned on by the large input. This has nothing to do with TRR (which is for ON->OFF transitions). This seems to mean that filter input amplitude transitions that rise above 12 volts must do so SLOWLY. Everything in the model seems to be doing what it should. The doubler doubles and the bias begins to rise when the input approaches 12 volts amplitude but it rises at different rates on the load side of the six 470k resistors with LPF0 being very slow and LPF6 being much faster. I have to raise the input amplitude slow enough to avoid turning on the LPF0 input diode. So, where am I going wrong? I have never used a PIN diode but I THINK I understand how they are supposed to function as switch. Is there something that keeps them from turning on quickly? Again, this is SURELY a red herring. But I would really like to make this work right so I have to ask. Thanks, Tony AD0VC

Took more shipping time than anything else. awaiting the return. Other than some of my ham-fisted soldering, he reports a bad PCM1804. This would coincide with the symptoms I observed. All the tests he did, and explanations in the email I got this morning, seem like I'm good to go. So awesome to have a resource like Jeff to support the QRP-Labs community. Can't wait to get it in hand! TU W1NC

This is not directly a question for this forum, but somebody may have worked it out: First: my QMX+ USB audio works great into WSJT-x on my Windows PC. Second: When WSJT-x is running on a Raspberry Pi 5, USB control of the rig works _but_, when I try to configure the audio, something strange happens. Under audio configuration, when I look for input devices, it show the QMX+ choices both as an alsa input device and an alsa output device. When I look for audio output devices, the QMX doesn't show up at all. Any ideas? I'm asking the same question in the wsjt forum. Thanks! -- Brent DeWitt, AB1LF Milford, MA

We had eleven folks join the MI QRP Zoom Chat on 22 May. Please join us Thursday May 29 (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 Pete WK8S Ed AB8DF Ernie NE3TE Tony W8CDC Stan WB8QJZ Casey KC9IH Larry AC8YE Dave N8SBE Harry K9DXA Randy KE8JWB Charlie NJ7V It was Randy’s first time. Welcome. Ernie purchased one of the new palm paddles at Hamvention. He was able to convert it to a kootie key. It was Charlie’s first time. Welcome Harry was at FDIM and did POTA on the way home. Both Ed and Ernie got a bunch of SMA connectors and cables because they got a WB2CBA Pocket Tuner at vendor night which uses SMA. Ed also got a ADX Pocket. The ADX is an Arduino based Digital Modes Transceiver. Stan wanted to know if we were able to get a look at the new Ten Tec rig. Yes there was one but we could not get a real close to it. It looked like a very rough prototype. We were also able to see the new Yaesu but just too many people to get close. There was a new Flex Aurora. Pete is going to do a Move-In special contest when this relocation is complete and has his shack up and operational. Standby for details. Dave has a AI6YM T41 kit https://ai6ym.radio/store/ We talked about the I and Q on a KX2 vs I and Q on a QRP Labs QMX QRP. Lab 599 has a new radio based on the Wolfe transceiver. The Elecraft K2 has an accessory that will do digital and one that will do a panadapter. Dave is working on doing a K4 remotely. The K40 is Elecraft’s top priority. Ekecraft is also working on a better noise reduction. The topic for Thursday, 29 May will be Field Day. The agenda for the 29 May QRP Chat: Ernie to do a short introduction and acknowledge any new folks to the Zoom chat. The topic for next May 29 will be Field Day. 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

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, I have released a version 2 of ABS solution. Please refer to the readme front page file at the git repository for full details and release notes: https://github.com/AC8L/QMX_Plus_Autotuner_Internal_Battery_Speaker/ The release includes new PCB fabrication files, BOM and detailed build instructions. This release took into consideration lessons learned and a feedback from first group buy participants fearlessly organized by Cal (AD8Q) and Stan (KC7XE). -- 73, Sardar (AC8L, 4K6SA, VA3DUA).

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

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

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.