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Here my initial test of the audio, sry in German :-) https://youtu.be/Xe_VNkaq-xk 73 Chris

I just did a bit of digging on electret specs. It seems that most of the ones I looked at had sensitivities down around -44 db (volts/Pa) with SNRs in the neighborhood of 60db. But the one that Hans specified is much more sensitive at -24db with SNR around 80db. This leads me to believe that grabbing a random electret is likely to give disappointing results. There are some that specify the sensitivity as a positive number (52db for example). I would take this to mean -52db. Either that or they have specifies SNR instead of sensitivity. Anyway, I was surprised to find that the one used by Hans seems to be somewhat atypical based on my quick survey of electrets. Maybe I just looked in the wrong places? 73, Tony AD0VC

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

I believe this is a question specifically for Hans :) Having recently had the receiver mux chips be destroyed seemingly without any other failure of the switching circuit controlled by Q508, I'm wondering if there is a potential race condition such that the transmitter "switch on" code may be reachable without the receive switch pin on the microcontroller being pulled low. I assume that transmit is almost certainly gated behind a command changing that pin state, but I'm wondering if there's a machine code level race condition that would let the transmitter operate without that pin being guaranteed pulled low? Just a thought, as this seems like a strange failure mode. Greg N1TR

I managed to get through the steps to build the RWTST version of the transformer. I'm getting caught up on Step 14: I have continuity between the secondaries. I also have continuity between the primary center tap and each of the two primary points on the left side. I do not have continuity between the two P points on the left side (i.e., the wires that were part of the hairpin loop before I cut it). Am I supposed to? Based on the wording in the instructions ("points P (P is for primary) should all show continuity to each other"), I assumed that I should have continuity between the two P points on the left side. Separately, do I understand correctly that the tighter the wire is twisted, the closer I will get to optimum power? I was able to twist them quite tightly, but it made them brittle for completing the coil. I tried again with fresh wire but I'm concerned that it's not tight enough. Thanks!

Thanks for all the SSB :) from The Hitchhiker's Guide to the Galaxy 73 DE muhsin TA1MHS

In operating the QMX+ with a non-resonant antenna and a manual tuner, it is unavoidable not to get the 'S' in the display to the right of the frequency from time to time. The 'S' just looks like some feature which has been turned on, but one quickly learns that it is an error message since the transmitter has shut down due to high SWR. By the way this is a very nice feature compared to e.g. the QDX and it has probably saved a lot of BS170's already. But my wish is that the 'S' could be made more visible - for instance that it would blink on and off - thus alerting the operator that something is wrong. -- Sverre LA3ZA http://la3za.blogspot.com

Hi, all - Is there by any chance a button push to exit from the menu system back to the operational frequency display, i.e., without having to do multiple EXITs to navigate up and out? [I think the answer is "no", but thought I'd ask anyway. If so, I'd like to suggest something like "long press of the MENU button while in the menu system will exit the menu system" ... very low priority, of course!] Thanks - Bruce K1FFX

QMX… I have the SSB software installed version three and made one contact with good audio reports. The only thing that is strange is sometimes the radio does not go into transmit when I press the PTT in Ssb mode. In CW mode it works every time 100%.

I was excited to try SSB on my QMX but my microphone was in my home QTH Michigan. I ordered the electret element that Hans recommended and assembled a microphone from spare parts. About $20. I downloaded 1_01_003 hooked up my 20M 1/4 wave vertical and looked for a POTA station to call. My first call was to a station in IL. I am in FL and got a 55. My second call was a station in Al and got a55. Now I can slow down and do calibration. What a blast! Mike Krieger

Hell forum, please your help, I am building my QMX+ V3. On page 30 of the assembly instructions, there is a table were L518 is 268nH with 23 turns on the pink T37-0 core. This one turn less than L516 (435nH) with the same core. Measuring with the nanoVNA, L518 with 23 inductance is about 100nH higher. To reach the 268nH, I have to reduce multiple turns. So here goes my question: Should I keep undoing turns until I reach the 268nH or should I ignore the nano VNA and keep the 23 turns? The same applies to L517, were the number of turns seams high for the target 316nH. The previous coils were very close to the target inductance. Thank you for your help, Luis CU2IJ

hi, i have been using my qmx+ for a month or two with success on ft8 on 20 & 10m. everything seemed fine. i have a battery power supply limited at 12v & current limited to 1.5A yesterday i decided to try to monitor & possibly send rtty during this weekend's contest. i uncovered the last transmit impediment in this forum (fldigi/modem/tx/transmit-shaping-OFF) and transmitted a few replies. i got 2 confirmations. then i noticed that the transmit power had dropped from ~4W to about 1.5W and checked other bands - indeed i had blown the finals. i replaced them. then i ran diagnostics - normally - i verified that the transmit power (into dummy load) was back where it used to be. thinking it was solved i went back to the rtty contest and during my first transmit - the power supply went into current limit & drew down the voltage to ~6v. i opened up the unit & couldnt see/smell anything, i lowered the supply voltage to 7v & current limit to 150mA. but when i turn on the QMX+ it immediatly goes into current limit. i was able to get to attempt a factory reset, but it didn't fix anything. so - i am hoping someone has a clue for me in terms of at least diagnosis. any ideas greatly appreciated! thanks lars.kn5ute

Very often when I do a Single click to change mode it changes band instead. I was wondering if there’s something I can do to improve the situation. Is this a hardware issue or a firmware issue? Is a common issue?

Hello Hans and others, I just uploaded the new firmware and am trying to get Winlink / VARA-HF working. Are there any specific settings that need to be adjusted? When CAT control supposedly keys up the radio, I can see activity on the signal bars on the right side of the display, but I do not get the bar or even two dots under the "A" on the left side of the display. Thanks, Darrell

Just updated my QMX+ to 01_01_003 Beta. Plugged a modified Baofeng mic into the front panel and tried running the microphone test. It doesn't seem to work. I can tap on the front panel, and that seems to get a bit of a response, but the mic is dead. Also, in USB/LSB mode, PTT doesn't switch to transmit. Hardware diagnostics indicate that the mic's PTT switch is working. Can see that the diagnostic notices the mic's FET... Unplugged and powered the mic from 10V through a 2K resistor. I can see audio with my scope, so that looks like it's working. Is there a setting I need to change, for the external mic to work? TIA! Paul -- AI7JR

First success yesterday with SSB on my QMX+ on 40m. Worked GB70RS at around 64 miles. He said the audio sounded good but to be careful of chewing the mic! 73 Tony G3OVH

On 3/24/25 I had a CW practice / rag chew session on 20 meters. I worked three stations: Date / Time Call Bnd Frequency Mode Power Rec Snt SPC# Name Comments Off 3/24/2025 19:25 AE4IX 20 14.054 CW 100 599 559 VA Rick K3 at 100 watts 100 ft sloper doublet 19:43 3/24/2025 19:11 K4WNY 20 14.054 CW 100 589 599 TN Ron K3 at 100 watts 100 ft sloper doublet 19:24 3/24/2025 19:08 K6GRD 20 14.043 CW 100 569 449 UT Rick K3 at 100 watts 100 ft sloper doublet Conditions were OK with QSB on all stations but better than it was on Sunday. SSN = 110, SFI = 168, A = 10, K = 3. My next CW practice session will be March 28 at 09:00 EDT / 13:00 UTC on 20 meters. Anyone and everyone is welcome. This practice is intended for operators who are new to CW or they need some practice. IT DOES NOT MATTER HOW POOR YOUR CW IS. Mistakes are OK. Poor fists are OK. Slow speed is OK. Really slow speed is OK. This practice is meant for you to improve your CW. I will do my best to adjust to your skill level. Operate at any power level. If several stations show up, I will operate as a round-table control station. I will do it as a round-table so everyone gets a chance to transmit. Please listen to my directions. Details: Date - March 28 2025 Time - 09:00 EDT 13:00 UTC Band - 20 Meters How to find me - I will find a clear frequency and call CQ. Go to the Reverse Beacon Network and search for my call sign AB8DF. That will tell you what frequency I am on. Tune your station to that frequency and if you hear me give me a call. If there is a QSO in progress, please wait for a break in the action. Then send your callsign. If I hear you, I will invite you to join the QSO and start a round-table QSO. Reply to this email if you have questions. IT DOES NOT MATTER HOW POOR CW IS Ed AB8DF_._,_._,_

Upon very first power up of QMX+ at 7V , there was no smoke, but the display only showed boxes. Adjusting the display trimmer only made the boxes disappear. Is there a troubleshooting guide that I might use? I have looked, but can't seem to find it in the documents. I know it's not much to go on, but any ideas where to start? Thanks. -- 73, Don K0DBL

I've purchased the 50-watt amplifier kit, to be built for 80m, and bought assembled the 40m and 20m amps from Ray, VA7SK (very nice solder job, btw); on 40m it certainly makes a noticeable difference of 6dB -10dB on reports and it's much easier to reach Europe. Question: Can I leave the amplifier inline between the QDX and the antenna if the amplifier is off? I'm not seeing that addressed in the assembly manual nor could I find an answer by searching the messages here. I think so based on the schematic, but I don't trust my circuit reading skills enough to risk the QDX or the amplifier. Thanks, Jim K8DDV

Hello, 80-20m is my first QMX Kit, QMX+ (160-6m) my second, now I purchased a 20-10m QMX Kit. I am using the QMX+ stationary, the smallones I want to use in portable operation. 80-20 and 20-10 means: 2x 20 m and no 6m band. The idea is to modify the 20-10m to 17-6m. The first thing I do is studying the schematics and creating simulations with the original L and in ngspice to get a feeling. If you are interested, here are the files: https://github.com/dl4pj/qmxfiltersim vy 73 Peter DL4PJ