Hi guys

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I have built a QMX+?

Wound for 12V.

FW 1_02_000

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From the get go, on TX, I have in my headphones a pulsing sound. No tone to it.

It’s a fast pace pulse. Maybe 3-4hz. When using the SWR tune tool the led on my ZM-2 will flash at the same rate.

Keying the mic and listening on a SDR I can hear the pulse in the background. I am unable to hear it in a CW tone on the SDR but it is in my headphones on SSB and CW.

The pulse does not toggle the rf, it just seems to be embedded in it.

On the face of it. It transmits fine.

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Randomly I get ear bending white noise on start up.

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(My QMX build went fine and its functioning well, go figure)

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Hoping someone might have a pointer on this.

Have dummy load, dvm and power is meter on the way….

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Thanks in advance. Ian. ZL1HIM

Two comments:

1.? If calibrated at a lower excitation voltage then operated at higher excitation there will be co compensations for the higher voltage.? This is the same as if a calibration does not complete.? Hans assures us this is fine if not perfect.

2.? At 80m and particularly 160m at full power the voltages caused by reflections from the LPFs back into the BS170 exceed the manufacturers rating, so if your not competent at replacing BS170s that may fail I ould not calibrate for those frequencies.

Unfortunately I have misplaced the voltage pictures.

That's too bad.? This is the first one I've heard of with the wire broken from the factory.? Chips off the top are common, and don't affect performance.

If the broken wire happens to be from an outer winding (rather than the inside), you can readily fix it by unwinding a turn or two from the coil and soldering the wire to the end of the adjacent capacitor (where the connection goes per the schematic).? I have done this on one of my units when my poor handling broke the coil wire.? A turn or two missing from the coil doesn't affect overall QMX performance.

Stan KC7XE

Thats what I said I have to reach for perfection in my build couldn't help myself ?

No, Mike, you don't want to do that, unless you also want to run the QMX at that lower voltage.

This is because the calibration routines store the phase compensation values for voltages across the full modulation range - and you don't want the high voltage ones to be empty, since it may cause distortion when those voltages are used in operation.? So you want to run the calibration at the highest source voltage that you will run your QMX in operation.

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Note that the majority of QMX/QMX+ devices have no problems with the calibration.? I have 2 QMX and 2 QMX+, on which I have run the calibration many times without any issues.? [I ran them many times during the beta period, due to updates and working around early calibration problems.]? So the odds are in your favor.

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But for some as-of-yet-unknown reason, there is something about certain QMX/QMX+ builds/units that makes them sensitive to the calibration procedure, and the finals and sometimes the PA voltage modulation transistor Q507 burn out.? Hans already made several changes in the firmware to reduce the chance of it happening, but for some reason on a select few QMX* it still happens.? Some conjecture that it is because of already-weakened finals, an already-failed Q507 (but in the release code Hans put in a check for that one), voltage spikes from L502, a poor connection to the dummy load, or other build-related issues - but nobody really knows.

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So if you definitely do not want to take any chance of breaking your QMX*, don't do the calibration.? The SSB performance of QMX* will still be very good. ? If you have a greater risk tolerance, and are willing to change the very inexpensive PA transistors if they do blow, then certainly do the calibration and enjoy the 'better SSB performance' that is promised.

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Stan KC7XE

Would it help to feed the QMX under update with a lower voltage, so as to reduce the strain on the BS170's during calibration?? For example, if I feed my 12V QMX with 9V, the power drops by about half.? I assume some of the issues during calibration are due to high transmit duty cycles that occur during the calibration process.??

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I did successfully run calibration on my knock-around QMX.? Fed it to a 50 Ohm dummy load and didn't encounter any issues.? But when I update my daily-driver QMX, would reducing the supply voltage help to add margin during calibration???

Thanks Richard for the reply, but further checking also highlighted the thread breakage. Honestly, I don't understand how it happened to be and it's not cikpa of transport. I'll ask Hans Süuto to solve the problem.... I was excited to get started.

ABS version 1.2 was released by Sardar late last year.? Detailed info is at:

Cal and I did a group buy of the boards and components near the end of the year, and I produced some additional documentation that you can find here:

This build works well for all 3 functions (battery, speaker, ATU) when you do the adjustments shown in my build notes and FAQs.?? It is a nice addition to QMX+.

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Sardar also released a ver. 2.0 this year.? Please see this message post by Sardar, and also all of the messages in that thread:

The ver 2.0 detailed information is in the link in that first message.

Cal and I have also built this ver. 2.0.? It is nicer in form factor, is easier to assemble, and solves some of the issues encountered and worked-around in ver1.2.? But we have encountered some performance issues with the ATU on 6m, and to a lesser extent on 10m and the lower bands, somewhat similar to those we found in ver1.2.? We started testing and trying to evaluate whether the performance is good enough or if there is an easy workaround to improve it, but we have been side-tracked with the many other priorities in our lives for the last few weeks.? We may also do a group buy for this ABS ver 2.0 solution, and have been keeping a list of interested parties.? But it will still take some time, because we want to make sure it will meet people's expectations and be at least as good as ver 1.2 before doing a group buy, but we haven't had a lot of time to spend on it recently.? If anyone else wants to do some pioneering builds and evaluation of ver 2.0, that would be great.

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Stan KC7XE

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The consensus seems to be it doesn't affect it at all. If you have the little piece and it bothers you super glue it later. You can search on broken coil etc.

Do not do it if your not comfortable.? Hans said calibration is not required and the unit works fine in SSB without it.

Received the kit from FedEx in a perfectly intact box.?

The content check was positive with the exception of the L501 inductor with the partially broken edge. Can this defect affect the operation of the kit?

Ludwig,

I see. Well I decided to send it off to Jeff (W1NC) to have it fixed. If it comes back working, I will NOT be doing the SSB calibration again, that’s for sure.?

Thank you for your input. Much appreciated.?

73,

Robert VE7ZN

I just built a Pacific Antenna mic kit for my QMX+ and it works great!! If you need a mic for your QRP-Labs transceiver kits I would look at this unit. Very simple to build and inexpensive.?

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73/GL

What power source were you using?

Hello, I ordered a fully assembled QMX in April, and got it about two weeks ago.? It died while i was listening to it. I maybe have listened to it a half hour total or less. i was switching bands and got a real sharp noise from my speaker, and then the screen went blank. not sure what the problem is, but i have only listened with it, and haven't even transmitted yet as a dont do cw yet, and i was building a mic for ssb. I was hoping to try digital modes on sunday, but i was just about to tune in to see if i could hear the 10m FT8 band as its a nice and sunny day, and i haven't been able to even hear ft8 on 10m as of yet. but its been pretty stormy here when i have been able to look at it during the week.

I have not open it up as i am not sure if Hans will want me to return it as is since it is so new, or if im stuck and have to repair myself.?

I really dont think this should have died after only about 20 minutes of just listening to it. i know things happen, but i would have just bought the kit. It did turn itself off a couple times randomly before this.? TBH i thought this was just my battery turning off since the draw is so low on receive.? but maybe there was a problem in the first place?

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I did measure a resistance a couple places, and battery terminal is fine, but the antenna to ground is less than a half ohm?

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also not sure how to contact hans for what to do, but i replied to the email sent and tried the "help ticket" but not sure i should message him here?

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thanks,
Ted

Hello all.? Just received my pre built QMX low band today into the US via DHL Express.? No tariff / brokerage invoice attached.