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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

By doing this you recharge the pack with storage function and will have only 3.85 volts per cell at the end of the charge for a total of 11.55 volts. Another my hobby is rc airmodell and normally put in storage mode the cell packs when finished the flights. I use charter M6 by toolkitrc. 73 Luca

Hi, I installed the 1_01_003 beta firmware yesterday and I am amazed at how it has transformed my QMX+ (rev 2 board). I am, however, perplexed at the fact that the SSB audio is distorted (on another receiver) only on 20M. This only occurred after calibration and the audio becomes absolutely clear again after disabling the phase predistortion. All other bands have good audio with and without predistortion, and the RF output is within normal limits on all bands, although 20M is a little lower than others at about 3W. I am using a 12V stabilised PSU and a good dummy load, via a Bird isolator, giving me a solid signal into my receiver. Trying to think of an explanation made me consider that the LPF used for 20M (LPF 3) may not present a good load to the PA, so I looked at the LPF sweep using PuTTY. Here is the sweep for 20M: The 14MHz line is in a less than ideal part of the curve, whereas the bands which share this LPF are better placed. Is this significant? The phase calibration sweep for 20M also looks odd and is different to the others which are all nice curves (except 160M which sounds fine!): This is the 20M USB IMD sync optimisation curve, the title of which has been overwritten by the asterisks of the curve. The 20M USB curve looks identical: Here is the adjacent band 30M curve for comparison: Everything on the board looks good and the radio otherwise works perfectly. I am perplexed at why only one band is distorted (it really is unreadable) yet 160m, which has similar calibration curves but a great looking LPF, Sounds OK. Any ideas? The simple answer is to switch off predistortion, but that doesn't solve the problem! 73 Ellis GM4GZW

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).

GM QDX’ers. I was gifted a QDX still in kit form so I spent a day building it this week. Except for one band, 80M, I got between 4.8 and 5.4W output which is optimal. The cure for that was to just put some more heat and re-solder leads on the inductors. I get reports of anywhere from -2 to -20. My issue seems to be with the received signal getting into WSJT-x. Although I’ve made a dozen or so contacts on 20M and 30M, the db meter (I’ll call the S meter) barely hits 15db maybe 20db on a real strong signal. Never higher. Most signals reports I give out are in the -17 to -10 range which would correlate with the db meter. I know from experience it should be a lot higher than that. I’ve seen no signals decoded on 40M or 80M but I haven’t listened at night which is going to be the most likely time to see those out in the NW. I’m using a retired MacAir as the computer using OSX. All radio and audio settings are set to the QDX settings and to full audio by default. The Radio is set to a Kenwood TS-440. It gives the impression there is not enough signal/audio getting into WSJT-x but I’ve got no way to adjust that. The antenna is a hexbeam for 20M and a 100ft high loop for 30/40/60/80 The version of QDX is 1.4 Any insight into this receiver issue would be greatly appreciated. I can live with the way it is now but I think with the receive signal stronger, it will show me a lot more stations. It may be MAC thing. I just don’t know. Thanks. John / K7RLD

With the official SSB firmware now supporting 3 virtual com ports, are we able to use the soundcard and I/Q at the same time? So can I do digital modes and have a panadapter? Would I be able to use IQ for a panadapter and still be able to use my mic for SSB? Thanks Randal VE7NHW

I have two QMX rigs, one I built (mid band version) the other I ordered assembled. The one I built was successful with the SSB calibration. However, the one that I received assembled from QRP Labs (high band version) fails the initial phase calibration on 20 meters, but passes on 17, 15, 12, 11 and 10. After which the all the bands calibrates fine with USB and LSB. I'm not a big SSB phone guy, but out of completion I would like to know if I should send back the High band QMX. I did the configurations via a USB cable and Putty in Linux. I haven't tried to initiate the calibration via the radio tools without being connected to a computer. Any suggestions?

I needed to replace one of the 1n4007 diodes in my QMX (I cut the lead for an experiment) so I went looking for a replacement. None of the 1n4007 diodes at Mouser have the small diameter leads like the ones from QRP Labs. They are all about .7mm diameter where the QRPLabs diodes are more like .3mm. I ended up ordering Vishay diodes with the fat leads. I had cleared the holes with the solder sucker but the leads still did not fit so I used some PCB drill bits to clear the holes and finally got the diode in there. Hopefully the via barrel is still intact. I am waiting for some caps to put it back together and try it. Any discussion about these diodes? My experience is that 1N400x diodes all had fat leads. Thanks, Tony AD0VC

Hey everyone, short story: After one of the PA transistors died, I replaced all of them. Now I only get 3,5W power on 80m but less than 0,5W on the other bands. Is this because of insufficient (fake) replacement transistors or could something else be damaged? long version: I built the QDX and after some wire pushing on the coils I got 5W@9V at all bands and was super happy. I am measuring DC on the detector diode of a QRP dummy load. After a some FT8 operation using an antenna, the output power dropped to 2.5W on all bands. Then I accidently shorted one of the transistors during some measurements and the output power went to a few mW. I removed the BS170s from the circuit and measured them using a diode tester and one was definitely broken. Then I bought replacments for the BS170 transistors at three different online shops (not really trustworthy ones). However during testing after replacing the transistors, the QDX behaved identically with each of the different BS170 sets. There was about 3,5W output power at 80m but only less than 0,5 W on the other bands. I supect that the transistors are fake because their performance decreased with higher frequency. But I am not sure. Is there a way to validate this? I used a LCR-T4 transistor tester to measure the transistors. This showed differences in capicatance. The original BS170s from the kit have 50pf, one of the sets I bought has 60pf and the others 30pf. Does this give any indication if the parts are correct? Or could it be possible that someting else in the QDX is broken? Maybe the IC that drives the PA (74ACT08)? However, I measured 2.5V at the BS170 gates so I guess it still works. Unfortunately I do not have an oscilloscope at the moment. Or is maybe the PIN diode switching circuit for the LPFs not working anymore? Reception is still fine! I would be really grateful for help on finding the issue! regards Chris

I wanted to try using WSPR, but every time I reboot, I have to set the time on the QMX again. A friend told me there's a GPS module that can help calibrate the QMX's time. I thought to myself—my phone already has GPS, so why buy an extra GPS module just to set the time on the QMX? So, I added a feature to calibrate the QMX's time through FT8TW. https://youtu.be/l8dey0vc6_E

Jeff has done it again! Repaired my mid-band QMX - a couple suspected cold solder joints and improperly wound T507 (how’d I do that?). Included was a free wax and polish (Jeff removed caked solder flux and scrubs the board with alcohol). All done in a day or two. I had my QMX back in ten days (could have been faster but that’s our slow postal service). it is so nice to know that Jeff is available to bail you out should your build fails. I’ve built two QMXs and he’s made them right for me. Thank you Jeff! And Hans! (his info is on QRZ) Phil K3UT

This seems to be a complex problem because I do not understand what is happening. I will try to explain as best as I can. QMX mid bands built for 12 volts and Z-11 Pro auto tuner. I start on 40 meters and go to hardware then SWR tune and start the tune. The tuner light move and ends when a <1.5 SWR is reached. I then go to iambic and send CW at about 20 wpm. After about 10 dits the tuner jumps up to over 4 and the S protection letter shows on the screen after the last number. I cycle the menu, go to hardware, SWR tune and it shows <1.5 SWR. I go back to normal CW and the same pattern shows up again. It happens on multiple bands and is frustrating because I can't complete a POTA contact let alone a ragchew. My sBITx is also low power 1 - 4 watts and does not do this action with the tuner. Any ideas where to look? 73, Dean/ N2TNN