Re: Tune SWR on QMX+ always shows SWR <1.05
On Thu, May 22, 2025 at 09:44 PM, Stan Dye wrote:
That's why I recommend to carefully scrape or burn/sand off the enamel before soldering the coil wires, which avoids much of this issue.
I think that the assembly instructions should recommend this approach, I think folks are poorly-served by encouraging use of the burn-and-pray method, it just fails too often.??
Perhaps it works OK for the QRP Labs elves, who do it all of the time and learn the technique, but we keep hearing the same cries of woe about open transformer connections ad infinitum.
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Hans, please change the instructions!
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73, Don N2VGU
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Re: FDIM 2025 - Bringing SSB to the QMX (Hans's presentation)
Hans explains it so well, I almost understand it.?
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Re: Solder pot for toroid leads
I'd like a solder pot, but it will have to wait until I have a bigger workspace and that day may not come. My bench is so cramped that I think a pot of melted lead would be a rather dangerous thing to have on it! As is, I'm always tripping on cables or catching wires with my sleeve. So I scrape, sand and tin.
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While waiting for my QMX+ kit to arrive, I bought a small crochet hook but my first attempt at using it was a disaster and since my wire supply was limited, I wound with the normal method. I still screwed another toroid up, but caught the mistake before soldering it in...I still ended up with about 13" of spare wire when finished. Which is still sitting on top of my washing machine and no doubt driving my wife crazy.?
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On Thu, May 22, 2025 at 09:35 PM, Jerry Gaffke wrote:
Could be process variation between different manufacturing lines for the BS170?
Could be variations in cap and inductor impedances for the LPF?
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Probably more likely different load impedances and/or latent failures due to electrostatic discharge or poorly-regulated or excessive supply voltages.
73, Don N2VGU
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It has already the AGC board, see just below the "s" of Labs.
73 - Pierre - FK8IH
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Re: FDIM 2025 - Bringing SSB to the QMX (Hans's presentation)
Thank you for posting. ?Really enjoyed a peek into Han¡¯s world and creative problem solving.
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On May 23, 2025, at 17:49, Muhsin TA1MHS via groups.io <muhsin.dogrular@...> wrote:
? Enjoy
73 DE muhsin TA1MHS
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Re: New QMX+ Calibration victim
One person's experience:
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I use a current and voltage limited supply when first testing kits. However, after I confirm that all is working properly, I go to battery power thereafter. All of my subsequent updates and testing is done with full power.?
I have not had a failure of finals in 12 QRP Labs tcvr kits. I have had various early failures (infantile part failures?) but none after those were addressed and fixed.?
Excess power and poor RF matching can certainly attribute some of the failures, but I don't think running on battery or any full voltage p/s explains failures.?
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73, Dan? NM3A
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Yes Stan, that is the scenario. When listening on headphones to relatively weak signals in, for instance LSB mode...to change to another mode you can only click forward passing through Digi mode. In my case and the same for others posting to this group, audio is painfully loud. I don't believe that I have changed any settings other than the band configuration overall audio gain. I do not support the use of AGC for digital modes either. The difference in headphones levels is the problem. If the levels for LSB, USB and CW were higher, the end result would be the same as by reducing Digi level.
de VK6XT?
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Re: QRP Labs kit shipping status 20-10 FS
The price of success!
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My Factory built QMX hiband can be in your hands in a week or so. 12- volt build, enclosure, .027 installed. Works perfectly.
Email sfab43@ho**ail.com for more info. Steve JS6TMW/AI6KX
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FDIM 2025 - Bringing SSB to the QMX (Hans's presentation)
Enjoy
73 DE muhsin TA1MHS
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Re: Solder pot for toroid leads
I don't do that because some wire has enamel that just doesn't melt. Also, it smells like feet! I use a box cutter and scrape it off. I also use the Crochet Lock method to wind them. On the T41, there's a boatload to wind, but
 the Cochet Lock lets me wind them at about 1/minute. I scrape the lead end that passes through the core first, then scrape the second lead after I've finished winding the toroid and trimmed it to length.
Jack, W8TEE
On Friday, May 23, 2025 at 02:12:56 PM EDT, Roy Ashkenaz via groups.io <cqk2rma@...> wrote:
Does anyone use Solder pots for tinning and removing the enamel from the toroid leads? Any hints and tips?
I see a cheap one on Amazon for about $20. Any suggestions if I should buy special solder for this, or use my normal Kester 63/37 solder in it?
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Re: SSB Cal problems with QMX (not +)
Randy, a couple of comments that I can give.
1) I have 2 QMX+ and 2 QMX (one low-band rev1, one mid-band rev3).? Each of these units had quite different looking plots for some bands of the calibration, some similar to what you describe.? And some bands didn't finish the plot during cal.? I was able to get most of the bands to 'finish' by repeating, sometimes changing other parameters.? I didn't really keep track of whether the QMXs performed substantially differently than QMX+.
2) I did have one band with the "change over 30 degrees" issue.? This may be a firmware bug.? Check and see if the "change over 30 degrees" was really a rollover from near 360 to near 0, which is really a 1 or 2 degree change.? When I investigated mine, I found that the firmware rollover logic was working in one direction, but not the other.? I reported this in a previous post late in the beta test period.? Then later I discovered I had a bad dummy load connection on that QMX+, and repeated the cal without encountering that same error - but I don't remember Hans saying he addressed the rollover issue in the release firmware.
3) I also see widely varying Y-axis values in the IMD cals.? Most bands dip to low values, but some are in the millions, like you describe.? And for a few bands there isn't a dip in the middle, it is still dipping when the cal maxes out at value 74.? Hans said finding the 'low value' or 'dip' is the key, and that the vertical axis value was not important.? The vertical axis is, though, from his description, some measure of IMD products - so maybe those bands have a higher total IMD, or maybe it is just a sensitivity to his measurement mechanism.
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In the release firmware, Hans made a change so that if a calibration didn't complete, he filled the rest of the data structure with 0s or valid data.? Previously it was uninitialized, and could result in distorted speech signals.? But now it should be fine.? So test your SSB output on the different bands - you will likely find it is just fine, regardless of the strange cal data.? I would check carefully on the bands with that 'over 30 degrees' issue, in case the error there prevented his logic that does the fill.
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My QMXs appear to still work fine with SSB, regardless of the strange-looking cal data on some bands.? So you may be fine.
Stan KC7XE
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Re: R520 Wrong component value.
This does happen sometimes. I recall some years ago, when I was building a Heyphone, and checking each component before I fitted it, I found that an entire batch of resistors labelled 4.3 K were in fact 4.7 K. As they were used in the phasing part of the transmitter this would have given odd ?results.
I raised the matter with the supplier (a very well-known company then). They apologised and sent me a full set of correct value resistors.
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On 23 May 2025, at 15:28, Stephen 2E0WSF via groups.io <2e0wsf@...> wrote:
When testing my
newly built QMX+ I was getting high SWR readings while running the
diagnostics SWR test. Even when connected to a dummy load the
readings were around 2.7 to 1 across all bands. ?I removed and
re-wound T507 (twice) but could not resolve the problem. So I removed
T507 for a third time and started to check component values around
the bridge circuit. I found that R520, although marked as 68X (49.9 R)
, actually measured as 124.5 K.
Has anyone else seen
this problem.
Regards
Stephen
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Sounds like you lost some connections to your front panel/display board.? Try re-seating the front panel in its connectors.? (Display and backlight are powered by 5V supply, and I think top row 'blocks' typically mean the processor can't talk to the display and initialize it.
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And regarding your 3.3V: in normal operations, the 78M33 is only used for about 1/2sec during power-on, then the processor activates the 3.3V smps to provide Vdd.? If you are also powering with 3.3V from the Drok, it could conflict with the SMPS, and confuse the processor (as it reads feedback on regulating the voltage), depending on how you hooked it in, and whether its voltage is a bit higher or lower than smps.? Did you connect it in via the diode that the 78M33 feeds (D103)?
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Stan KC7XE
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Re: QMX+: low RX sensitifity @ 6m / 22 dB noise floor / 1500 Hz wistle
On Thu, May 22, 2025 at 02:33 AM, KEN G4APB wrote:
I am a bit sceptical about ¡®cures¡¯ that cause problems to go away (or change characteristics), after resoldering. Surely a joint is either good or not connected.???
Not correct: a solder joint may be 'ok' for DC but poor for RF (or vice-versa).? Reflowing a solder joint, especially for the toroid wires that had enamel on them, can burn off the enamel around the full circumference of the wire, which will give a better RF connection, and improve RF performance.? This is partly due to the 'skin effect' of RF currents, which travel primarily on the surface 'skin' of the wire - and if all that 'skin' is not available, the current cannot travel as well through the connection.? It may connect and give 'ok' performance, but may also have limitations in performance depending on the circuit and use.
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And for what its worth, yes I also see the vertical lines on several 500Hz boundaries (when monitoring 50.313 on wsjt-x), which are most prominent on 6m - on both of my QMX+ builds, a rev2 and a rev3.? But these are really not a concern for me, since a) only the one at 1500Hz is strong enough to be annoying, b) FT8 and other signals still decode fine, even on top of those 'birdies', and c) I can easily tune my audio listening away from 1500Hz while doing FT8.
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My QMX+ was working but when I powered it on this morning the display backlight is not on and the display shows a row of black blocks.? Does anyone have any thoughts on where to start troubleshooting.??
+V or?+12v has 12v, VCC has 5.1v, and VDD has 3.3v.?
I have had some issues with this unit.? The 78M33 failed.? When I tried to remove it the two small pads lifted.? I currently have the 3.3v being supplied by a small DROC 3.3v buck converter.? It was working well as of yesterday, I completed several FT8 and SSB QSOs.
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Re: #qmx plus assembly one LP and Band filter at the time
#qmx
With only one LPF installed, it is hard to know whether the fault is 'global' for all bands, or just in the one LPF - so it is harder to know where to look.
If you measure resistance from cathode (line end) of D508 to cathode of D511, do you see a short-circuit?? You should if the toroids and diodes are soldered properly.
Also, on your LPF sweep, which you say looks ok, is the top level (left axis value) near 0dB, and the bottom near -20 or -30dB?? Sometimes the filter shape can look good, but the vertical axis scale wrong because of another fault.
Another check, if you test tx on 160 using the 'T' in the diagnostics page, what is the Transmit voltage and bias current reading, both before and after pressing 'T'? - does it just go quickly to swr protect when 'T' pressed?
Stan KC7XE
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Re: Solder pot for toroid leads
Roy,
? I use a solder pot. The only warning is that the temperature will need some adjusting for the different sizes and types of magnet wire. If it¡¯s too high, not only does it take off the enamel it also starts melting the wire. The one I have is similar to photo. I tested it and put sharpie marks on the dial for the different gauges of wire. It is also good for dip soldering antenna wires.
It is heavy so as not to fall or be pulled off of workbench. I only bring mine out when using it. You¡¯ll need a piece of stiff card stock to take ¡°sludge¡± off of top of molten solder pot. Look on the interwebs for tips to use one. I bought some Oatey 4 in 1 Solder Ingots on eBay to fill the pot. Hope this helps.?
JP
KA3BWP
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Re: Solder pot for toroid leads
Gently scrape the enamel, then tin it with solder. Nothing special required. I scrape mine with sharp dikes. Once it's damaged the heat of soldering finishes it.?
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Joe,
It is most often not useful to try and supply external 3.3V VDD - because the most common failures of 3.3V supply would also make an external supply not work.
With QMX+ and over-voltage, here are the things to look at first:
1) Inspect (and test if you can) the input TVS diode D110, right next? to the power connector.? This diode can short with over-voltage, as it tries to protect QMX+.? If it is shorted, remove it, and see if all works again, if so, you should replace this diode so it can continue protection - but the QMX+ will work without it.
2) If you can, set your power supply to about 7V with a 250mA current limit (this allows voltage testing without risk of doing damage)
3) Measure the power supply current when:
?? a) Just plug in power connector with QMX+ off
?? b) while pressing QMX+ power-on button
?? c) after releasing QMX+ power-on button
If the current at c) is somewhere between 120mA and 220mA, it is likely that your 3.3V supply is working, and you can connect with the PuTTY terminal and use the built-in diagnostics (even if your display is not on).? Your 5V? VCC may be damaged
If the current at c) is near 0, but very high at b), one or more of your finals may be blown/shorting - based on your description of the failure while not transmitting, I don't think this will be the case.
If the current at c) is near 0 and the current at b) is high, the D109 in your 3.3V smps may be shorted.
There are also many other possible faults from over-voltage, for which we need to do various measurements.
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And read this startup process to understand what goes on during the various stages of turning QMX+ on: /g/QRPLabs/wiki/36878With QMX+ r2 or r3, the 3.3V and 5V smps are built onto the board, but the test process at this link (which was written for separate smps boards), can give you insight in what to measure and test on you QMX+ smps: /g/QRPLabs/wiki/37128Good luck, and let us know if you get some measurements you don't understand.
Stan KC7XE
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Donald S Brant Jr
Lawrence KC6WOG
Pierre - FK8IH
jjpurdum
JP McGinley KA3BWP