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Hi All, Just wanted share my experience with you. I have experimented with 3 electret mic capsules so far. 2 that I scrounged off of other boards and one utilising the mic from my PC gaming headset. The mic from the head set resulted in low volume and unsatisfactory modulation. When I turned up the mic gain on the QMX+, the QMX also amplified internal noise creating unacceptable background noise in the modulated output. The other two capsules were a little better but still unsatisfactory. One of the capsules that I had took off was from a MAX9814 Arduino mic amplifier module. I thought, "Hey, why not use the amplifier module to use with my headset!" Well, I did just that. I wired up 2 x 1.5v AA's in series to power the board with and wired the mic from the headset as the input to the amp. I then wired the output of the amp to the mic input of the QMX via a 1uF capacitor to block the 3.3v dc from the QMX. Well, that done the trick! I'm getting much better results now. But I did have to reduce the mic amp module gain as it was way too high. As it currently stands, I am unable to achieve a satisfactory calibration with any of the bands on my QMX+. As a result of this, my QMX+ is in default calibration settings. The mic gain on my QMX+ is now set at 35 and have made a few contacts with good reports with this setup. Now, the question is, how do I wire up the mic amp module to the QMX using the 3.3v supply on the TRS rather that using batteries? I did try taking the 3.3v via 2k ohm resistor from the QMX TRS terminal to the vdd of the mic amp module, and connect the output of the module back to the same TRS terminal via a 1uf dc blocking capacitor, but sadly that didn't work. I'm clearly missing something... Cheers, Mel. M0KMD.

Hi, I've just finished my QMX+ rev.3 (firmware 1_00_027). Everything seems to be working correctly, except for the SWR and PWR does not show. They don't appear on the LCD, even though I have them enabled ON in the setup. The LCD display is working properly, showing the battery icon and clock, frequency, etc. Any advice would be welcome Thank you so much! 73 Miguel

After assembling a QDX rig for a local ham I received a couple of the QDX PA mod PC boards made by WB2CBA which have the FDT86256 mosfets. They have a max voltage of 150V compared to the 60V of the BS170. Since I like to experiment I decided to try and adapt one of the boards to my QMX+. I filed off the two "tabs" opposite the mosfets being careful not to file off any of the traces. It fit perfectly where the BS170's were. After some testing it seems to work well. My QMX+ is presently wired for 9V and I have a Buck-Boost converter stuck on the back set at 10V so I can use any battery I like from 5V-30V. On 80m-30m I can easily get 5w with the 10v input. Since I like to "play with fire" I plugged in my 12.6V battery and got 6.5w-8W on the lower bands. The mosfets stayed very cool....into a dummy load. While playing on FT8 with my Hexbeam and low SWR sometimes the finals got warm and actually got pretty hot on some of the higher bands but kept work fine. If anyone else out there can or wants to give it a try, especially if you have the proper test equipment please let me/everyone know what you found. The info for the PC boards are here... https://github.com/WB2CBA/QDX-PA-MODIFICATION/blob/main/QDX%20FTD86256%20PA%20Modification%20Story.pdf Tim - K5DEZ

Hello all, Long time lurker, first time poster here. I recently built a 60m-15m QMX and I am having some trouble getting good reception on 15m and 17m (see attached RF sweeps). I should mention that I am using a Rev 1 board purchased in 2023, but with a mid-band component kit from 2024. Here’s where I’m at: I get good power (4-5w at 12V) out on all bands, and my LPF sweeps look like the firmware manual 60m-20m RF sweeps look more or less like what’s shown in the manual. I use a QRP Labs 50 ohm dummy load for the sweeps. When I connect to an antenna, I can hear FT8 signals on 40m and 20, but not on 17 or 15 Because the lower bands seem to receive OK, I suspect an issue with L401a, C401 or C403. However, 20m uses L401a and C401 and is OK, but 17 also uses those and is not good. I reflowed solder on all 3 taps for L401a and the capacitors, with no change. I’m pretty confident I’ve burned off all the enamel at the junctions at this point. I get continuity at all the points shown in the Rev 1 manual (plus at pin 6 of IC402, which I think makes sense because I’m using all 4 connections for L401 instead of just the 3 with the low band version) I did a factory reset, with no change I’ve counted the number of turns on 401a more times than I’d care to admit, and keep coming up with the same number I’m supposed to have (24 turns, tapped at 15) I confirmed that C401 and C403 are the correct values printed on the component, and don’t appear to have any physical damage Trying to figure out my next steps, but coming up a bit short. All I can think of is to replace capacitors, and possibly re-wind L401a. Or, even less ideally, replace IC402. I don’t have an oscilloscope (or any real expertise to use one), so my ability to diagnose is somewhat limited. Before I start swapping out components, is there anything else I should try looking at? It’s been fun building this kit and I have managed to iron out quite a few kinks along the way by reading posts on this forum. However, this one has me stumped. Thanks in advance Alex, N7ADH