Re: QMX kit has a internal short at power up
You might check D109 (the 3V6zener on the #2 plug-in board. Mine was "soft" and although it began conducting a bit below 3.6 volts, it allowed the voltage to climb above 5 volts and caused a hard short to ground within my MCU pretty much like yours.
This is for my curiosity only. I haven't seen any offers of a loaded CPU yet and the replacement would be difficult even if it were.
At this juncture it might be best to order a new kit and start over. If you do then you might check D109 before applying power just to make sure. Couldn't hurt.
Please keep us posted if you find out more.
-Don-
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Re: QMX kit has a internal short at power up
Hello Martin,? I have the same problem,? see /g/QRPLabs/message/116603It seems that there is no ESD protection of the CPU at all, so that you have a good chance to kill it.? There was a discussion about providing CPUs programmed with bootloader by qrp-labs, but I don't see them in the shop.? Buying just a new board for $85 will not make much sense vs. a complete QMX kit for $95. The CPU is approx. $10 at Mouser or Digikey, but without the bootloader it will be useless.? -- 73, DB2OO -Joerg
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Re: QMX / Antenna tuner disagreement
Seems enough that you were to arrive at the reason.
Takes a lot more choking at lower frequencies.
--
Allison
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Post online only,?
direct email will go to a bit bucket.
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Re: QDX 10-20M Version - Soundcard Error
Hi Gil!
I had a brief USB failure as well on my QMX, but did not manage to reproduce the issue again so far.
I had an Iambic key connected to the QMX and configured as straight key to play with my LPFs. With this my PC and laptop failed to detect the USB (unknown device). As soon as the Iambic key was removed or the SW setting changed to Iambic, the USB detection suddenly worked again.
(It looked like some timing / SW issue and the QMX was busy figuring out what is happening on the keyer input and did not serve the USB device descriptor requests in time... - Wildly speculating here!)
So maybe try your USB connection only with power cable connected and nothing else and see if anything changes.
-Tobias
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Re: QMX / Antenna tuner disagreement
Allison, I didn't think those toroids would be enough, but I figured it wouldn't hurt to try. ? -- 73, Dan? NM3A There are moments when everything turns out right .... Don't let them alarm you; they pass.?
-Jules Renard
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I still think the least expensive, educational, and accurate mWattmeters are the ones from China listed on various sites like eBay for around $26. These use the tried and true AD8307 log amplifier which has been around for years and is known for excellent accuracy. They are all designed for 50ohm systems which is what we want. They can be powered by 6-12 VDC and run quite well off a 9V battery for portability.
The output is in dBm and very easy to convert to mwatts. Even easier if you use one of the Mini-Circuits "dBm-Volts-Watts Conversion Charts" available free online. Just search for? "dBm-Volts-Watts Conversion" and download from Mini-Circuits. DO NOT download the "free" print service from "One Source" because it will attempt to also provide a new browser to your computer.?Sneaky dogs. Also print several copies, they are as easy to misplace as 1/2" and 9/16" sockets. The mWattmeter has an internal 50 ohm terminator, so all you need is a battery, the mWattmeter, and the 30dB attenuator connected to your QMX/QDX rig output (and some cables)
The other thing you need to do is provide a reasonable non-inductive 30dB attenuator. A good 30dB Pi attenuator can be made from qty 1 CMF50787R00F and qty 2 CMF6052R300FKR from Mouser. They are both 1% resistors and the 53 ohm resistor is rated at 1W. You can parallel/series the 53 ohm resistors for more power if they get too hot.? The attenuation calculates to 30.01dB. 30dB is convenient because it will attenuate watts to mwatts. Keep any aattenuator leads SHORT so you don't introduce too much inductance.
73 Kees K5BCQ
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I also see similar results from the RF filter sweep at 20M on my HB QDX. The LB QDX has a mush different sweep. This difference is reflected in JTDX spectrums for the two radios - the HB receiver is considerably attenuated when compared to the LB radio. Screen shots attached - HB: LB:
High Band on 20M? 2047UTC
Low Band on 20M 2048 UTC
I now consider the HB to be a 17M-10M radio and use the LB for 20M.
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Re: QMX Low Bands Rev1. RF filters bad on 40m & 60m and no Transmit on any band
20m, 30m & 80m work on transmit and receive, just need to wait for the replacement inductor to fix 40m & 60m. Other bands do not work on transmit if preceded by trying transmit on 40m/60m a self protection circuit I guess.
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Re: QMX / Antenna tuner disagreement
At 7mhz range you need a FT43-240 (large core) with at least 22 or more turns of?
RG316 (or 174) to effectively choke the currents.
--
Allison
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Post online only,?
direct email will go to a bit bucket.
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Re: QMX / Antenna tuner disagreement
Garrett,
I believe you got it, spot on! I set up the antenna in the yard similar to my POTA setup. I got a very similar NanoVNA sweep with lowest SWR 1.15:1 at 7.060. Connecting to the QMX, I got 2.5:1 on the QMX. Touching the coax varied both readings.?
Five turns of the coax through four T130-2 toroids changed the readings, but still varied with coax touching. An LDG 1:1 unun near the antenna made a big difference in the resonance frequency (7.36), but touching the coax no longer changed anything. NanoVNA showed 1:16 SWR at 7.18 (after tuning to be in-band) and QMX then agreed!
Mystery (to me, anyway), SOLVED! Thanks to all who responded!
--
73, Dan? NM3A
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Re: QDX finals modification, imbalanced heating
Thanks Dean; the copper tape seems like a good idea, as long as the adhesive layers don't impede heat transfer. In my experience the adhesive is quite thin, and you're compressing everything too, so it seems good. It's nice that in yours there's more airflow between the neighboring FETs too. I put mine in with pretty short leads so there's not much mobility left.
The center heatsinks I'm still not sure about, given the previous point that the board surface there is actually designed to draw heat away from BS170s. However, my observations agree with yours that if you put a heatsink there it gets fairly hot on transmit. Worth digging into more.
I'm quite curious how your setup compares heat-wise. Do you also find that only operating 10m dissipates a lot? What kind of temperatures do you see for a given key down time?
Peter_Li, I just thought I'd share what my QDX heat sinks look like also. I found the heat sinks for the TO-92 case of the TN0110 MOSFETS were a bit loose and what I did was put three wraps of copper foil tape onto the MOSFET and then used thermal paste before pushing the heat sink onto them. I also installed a couple of stick on type heat sinks onto the board to help remove the heat from there too. When transmitting into a dummy load, I do feel heat on my finger from all of them. This may or may not be overkill by using heat sinks in both locations but I thought it couldn't hurt.
?
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Re: #qmx wrong inductances for LPF?
#qmx
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Re: #qmx wrong inductances for LPF?
#qmx
Hi Ludwig
FYI the toroids in QMX are purchased directly from micrometals in California, US (), in large quantities (10,000 or 20,000 etc). I have no reason to suspect they aren't the very best quality and with correctly specified AL values. If anyone feels the AL values are wrong then I'd be more inclined to suspect the experimental setup and/or measurement accuracy or some similar factor.
But it's tempting to overthink the inductance situation.?
Simulation is a good guide. Or calculation based on theory. In the real world there are frequently many other factors not accounted for theoretically. Results usually differ between practical measurement and theoretical prediction, sometimes only by a little, sometimes by a lot. Bear in mind measurement is subject to errors also.?
In all my work, if I use simulation or calculation, I consider that a first guide only. Then build and test. Then tweak things, see if improvement can be found. If the practical number of inductor turns differs from the theory, it doesn't upset me.?
The number of turns in the manuals are what we have found, experimentally, works best (for example with LPFs, power output and PA efficiency, as well as harmonic levels). Even so, there will always be some variation from builder to builder.?
The manual number of turns are my recommendation; most people can count, but most people don't have an inductance meter (let alone an accurate one at such small inductance values used in HF LPFs).
Having said all that... If you are confident of the accuracy of your inductance measurement for such low values, and if you wish to build it according to theory, I don't see any problem with that... And even better if you report back on your results, it will be interesting.?
73 Hans G0UPL
On Thu, Jan 25, 2024, 3:54?PM < DH8WN@...> wrote: Two more information:
1. All tests were made with turns spread over the whole toroid. So inductivity is lower than with turns pushed together.
2. Ref. to manual page 40 L508 should get only 11 turns and not 13. Calculate with 13 turns L should be 270 nH like shown in table (286 nH). I measured 270 nH when made with only 11 turns! So this points also to a higher AL than from the data sheet.
73 Ludwig
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Re: QMX / Antenna tuner disagreement
Sometime back I loaded .10 firmware into my perfectly functioning QMX only to have the same thing happen: high SWR shut down! This is into a tuner and antenna proven to be low SWR by nanoVNA and another radio. I asked the question last year when it happened "could I have a winding wrong on the SWR bridge to cause this?" Got no answer. Now today I see others here have the same problem.
I do recall a question about winding direction on one of the binocular ferrites and some answer that it would be solved in software.
I now have .14 loaded in the QMX and have been checking out the operation in receive. Have not transmitted anything as yet. Have disabled SWR PROTECT....
Will advise if I find anything.
--
73
Karl
KI4ZUQ
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Many thanks Allison for taking your valuable time to analyze my data. Yes 'troubleshooting by remote seculation' is indeed an endeavour with limited return on time invested (unless one gets lucky).?
The unit is not meeting the specification for power output. Thus I will continue to test all aspects. Next I will look into why the input SWR is high.
73 Dick N4HAY
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Re: QMX / Antenna tuner disagreement
Garrett, Interesting thought. I did not have a choke on the feed line. I used a 25' RG-174 feed line and was about 12' away from the antenna inside a closed vehicle. I could easily try the choke.? -- 73, Dan? NM3A There are moments when everything turns out right .... Don't let them alarm you; they pass.?
-Jules Renard
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Re: QMX / Antenna tuner disagreement
I have been out with the QMX many times and QMX SWR readings always agree with 4SQRP or ZM-2 reflected power indicators for various different antennas.
Chris: ?Dummy load always has shown 1:1 SWR on QMX and other analyzers. Did not check a dummy load yesterday, but today shows 1:1 as always. Did not do a QMX SWR scan.?
Allison: I was on 40m. NanoVNA was 1:3 at 7.050. I was at 7.058 on QMX. NanoVNA was not significantly higher at 7.058- it showed <2:1 from about 6.95 to 7.15. So bandwidth was not super narrow. Antenna had 102" whip above (Mini Wolf River) coil with 4 x 14' radials lying on ground in X pattern.?
The 4SQRP tuner does not have a bypass switch, so had to use Pi network for readings and therefore no direct correlation to analyzers.?
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73, Dan ?
NM3A
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Re: QMX / Antenna tuner disagreement
Possibly the effects of CMC getting into the QMX, that the tuner was able to shield it from. The 1/4 vertical isn’t going to have as much CMC as an OCFD, for example, but it is still an unbalanced antenna system.
I suggest trying again with a common mode choke (even just wrapping the coax with the connectors already on it through a sufficiently sized type -31 or -43 ferrite toroid) and seeing if it makes a difference. Or a decent sized clamp on with the coax passing through it as many times as will fit. Of course there are more elegant solutions for longer term use at QRP.
While you can often observe the presence of CMC with something like a rigexpert, by touching the outside (shield) part of the coax connector, and seeing if SWR jumps around while in measurement mode, the test device obviously transmits at very low power so effects of CMC are much lower.?
Just a suggestion. Best of luck.
Garrett Kc3Unp?
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Re: QDX 10-20M Version - Soundcard Error
Thanks, Bernie. Yeppers, tried that and different cables too. No luck. I have been pointed to a service technician who may be able to figure it out. I may have gotten a chip too hot, or something. It is a real puzzle but beyond my scope of skill to find. 73, Gil - KS4YX
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Don, ND6T
Karl
Garrett kc3unp