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20% is a typical tolerance and if you have an inductance meter it’s better to go back to the theory calculated inductance values and check them as you wind?
(That said it’s common to see ‘off values’ result ?in practice for output (LPF) filters as they are tweaked to provide matching as well as filtering ) |
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Re: QMX - smoke - another C107/Q108 failure
Hi Jonathan, Kees These plots supplied by Jonathan look completely normal to me.? The 3.3V rail experiences some disturbances during the boot-up process and this is completely normal; it is powered by the 78M33 linear regulator during that time via a 1N4148 diode. The diode voltage drop will naturally?show some variation depending on current draw, and current draw will be variable as the unit boots up various things.? 73 Hans G0UPL On Mon, Aug 28, 2023 at 6:27?PM Jonathan Burchmore <burch@...> wrote: Kees, |
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Re: QMX - smoke - another C107/Q108 failure
Hello Stephan ? I think that given all of the people experiencing blown components due to power supply issues (including myself), there is a case to be made for a redesign of the power supply. Something like an can replace 38 parts in the current design with 8, with significantly better performance in every way. The frequency of the part can be externally synchronized, but you can also simply configure it for 2.2 MHz, where every harmonic is a minimum of 400 kHz from any of the amateur bands covered by the QMX. Yes but...? 1. What about the eye-watering price? There are two versions in stock at Digikey, LTM8078IY and LTM8078EY. The price at 520-quantity?(1 tray) is $11.52 and $10.47 resp. Plus taxes of course... for comparison, since I have the two SMPS boards on the QRP Labs shop at $10? I'm sure you can imagine that the parts costs are way way less than one of these LTM8078; consider that the $10 price also includes the 6-layer PCB, the two female header connectors, SMD assembly factory costs, shipping, taxes, other costs etc.? 2. One of the main reasons for using a discrete component buck converter when the QDX Rev 3 PCB was designed, having the discrete component buck converter for the PIN diode forward bias generation, was that the global semiconductor crisis was in full swing, and adding an unusual part to the BOM seemed distinctly unattractive compared to a handful of discrete parts which are much easier to find. The QMX design inherited the buck converter from QDX. Whilst the global semiconductor crisis has receded somewhat we are still nowhere near back to the old days where you never ever thought about availability because you never had to. Looking at the available stock in Digikey (1050 of the EY and 3410 of the IY) isn't terribly encouraging in that regard.? 3. Being a BGA package, replacement would truly be beyond the reach of most of us here... 4. We are getting through building a larger and larger number of QMX now that the whole team are building them here. Originally, while we still had a long list of QDX, QCX-mini and QCX+ on the waiting list, only one (the most experienced and accurate) team member was building them, in order to build up experience of potential hazards. Of all the QMX I have yet seen, other than the Q103/Q104 Drain short (manufacturing problem) I have yet to see a failure that is not attributable to shorts, damaged components or other construction errors.? 73 Hans G0UPL |
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Successful QMX build - and some bug reports
#qmx
开云体育Dear all, ? many posts discuss issues with the QMX build (shorts and holy smoke) and as reader one may get the impression this is normal. Well, I just want to share a successful build story. It was my second kit after a QCX-mini earlier this year, so I would not consider myself a very experienced builder. ?? Overall I had no build issues, got good RF sweeps and between 3.5 to 4 W power output on all bands “as is” – no toroid fiddling (12V build). I see around 150mA current draw when switched on and receiving (backlight on). Several FT8 contacts done on 40-30-20. Below the reports on 30m this morning (~30 minutes operation using a pre-tuned random wire): ? ? ? @Hans: Some bugs I observed so far: ? In Digi mode (FT8):
? In CW Mode (actually what I want to use the QMX for): Audio issues:
? CW Settings:
? Otherwise I’m eagerly waiting for:
? Thanks Hans for this nice kit! Matt ? |
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When previously using iron-powder toroids I've always had close correlation between measured inductance values and those obtained from the published tables and on-line calculators. So when doing some development of a [40m/30m] LPF for my QMX I was surprised to measure inductance differences between 10% and 20%.? For example the calculator at toroids.com shows 440nH for an 11-turn coil on a T30-6 core with 25mm pig-tails. But with the T30-6 supplied with my kit I'm measuring 529nH with pig-tails of just 10mm. It's the biggest discrepancy I have ever seen. It's not a problem for a one-off design checked on the bench. But if this is typical then there may be consequences for production repeatability of LPFs, especially any that use a "notch" to pull down the response at second harmonics. Has anyone else measured similar discrepancies?
(I'm a 30+ year professional user of VNAs and am freshly calibrated at the measurement reference plane with SMA short, open & load. And I am counting the turns by the number of passes throught the toroid centre.) |
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Re: A weird problem
On Mon, Aug 28, 2023 at 01:06 PM, Leland Lannoye, W9HIF wrote:
I have a weird problem. No waterfall. The rig goes through normal fire up. Don't know if there is output or not. I use my tablet, ft8cn and an end fed log wire and am on 7.074 mHz.Leland!? I noticed you corrected Billy (N5SE) on his grammar/spelling. You might want to run your own posts through the same quality control.? ? Just jesting..... To which rig are you referring? |
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QDX Rev 4 Only Shows 80M Band After Working Near T2
After doing some rework on T2 my QDX it only shows 80M in the band config, the other bands do not appear at all. Normally there would be 80,60,40,30,20 with a whole set of options for each but I only see 80M.
I happened to reflash to an older 1_05 firmware and the bands all show up when running that version but disappear again on 1_10. I have done a factory reset with no change. The diodes all go to 0.6-0.7v for the corresponding bands when I test them on 1_05. I'm guessing I did something to an SMT component around T2. The parts are very cheap but I'd like to know what one(s) might be involved and I don't want to attempt to repair something if the fault is elsewhere. I've read through the documentation and I didn't find any mention of band detection/enable aside from the jumper wire if it was a high band model (mine is not) Does anyone know what components or connections would make a Rev 4 QDX only show 80M on 1_10 but be ignored on 1_05? |
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Re: QMX: Kit build trouble, a short between A & B for Step 17 of Section 2.9
370 kOhm as in kilo-ohm? That's the opposite of a short. Installed in the circuit, there is about 10k of resistance between the primary and secondary windings of T501 because the primary is connected to ground through R508/9 and R525/6, and the secondary is connected to ground directly. This is the peril of trying to measure any component in circuit, because you're not just measuring the component, you're measuring the circuit around it too.
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Re: QMX working FB then shorted out. Ideas?
A thermal camera is hands down the best way to identify a shorted component. Turn on the power and look for the thing that glows. You can get one that attaches to your phone for about $2-300. |
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Re: QMX working FB then shorted out. Ideas?
开云体育Well, pulled the finals and still draws 700mA when the left encoder is pushed. It stays there until I kill the power to it. No display backlight.Other things to check? I hate to pull the driver chip with out good evidence of a problem. Is there a way to check things further? 73, Cliff, AE5ZA
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Re: QMX - smoke - another C107/Q108 failure
I think that given all of the people experiencing blown components due to power supply issues (including myself), there is a case to be made for a redesign of the power supply. Something like an can replace 38 parts in the current design with 8, with significantly better performance in every way. The frequency of the part can be externally synchronized, but you can also simply configure it for 2.2 MHz, where every harmonic is a minimum of 400 kHz from any of the amateur bands covered by the QMX.
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Re: QMX working FB then shorted out. Ideas?
开云体育Jeffrey,I'll take your word for it. I've blown the finals on the QDX and it was just low power out. I guess the QMX is different. That sure is an easier fix than some other things. I'll just pull the finals and if it will power up then I'll know they are the issue. 73, Cliff, AE5ZA
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QMX: Kit build trouble, a short between A & B for Step 17 of Section 2.9
I started building QMX following the instructions carefully. I've been checking the solders in every step. |
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SMD 10k resistor, 103 replacement for QCX mini
Brad McDowell
I picked up a QCX mini, 20 m, revision 1 at a ham fest.? When building I noticed the R46 resistor was badly placed and cracked.? It looks like a factory error when placing the SMD's.? I need a replacement of the SMD 10k resister, labeled 103.? Mouser has about 20 options.? Can anyone point me to the correct SMD resistor so I can repair this kit.
Thanks,? AB4BA |
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QMX substitute for Q103
The Q103 FET was broken In an attempt to move it, 'D403'.? I have several AOD21357 FETs that appear to have virtually identical specifications.? Can they be used as an acceptable substitute for Q103?? Hopefully someone other than Hans will answer, he is surely too busy to bother with this question.?
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Re: QMX successful so far - power chase
开云体育Yesterday I activated a POTA and took part in the Skeeter Hunt with 10 contacts in 7 States and the RBN reporting me 3750 miles away using my QCX-Mini and a homebrew 20m (46”) Mag mount. ?My power after the tuner was just 3.5w or so.My point is....... don’t sweat trying to squeeze out the last mW, it’s the ears on the other end and YOUR antenna that is most important. JOHN KK4ITX? The QCX-Mini is a great machine and I bet that the QMX is better in many ways too !! John KK4ITX? On Aug 28, 2023, at 20:20, Sandy <mac3iii@...> wrote:
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Re: PTT over CAT in WSJT-X no function, does not transmit in FT8
Set the "power" slider in WSJT-X all the way up. In the digital mode the QMX is not modulating SSB. Its doing true FSK, based on the tones on the input. If they're below the threshold to decode, there's no output.
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73 de K9ID On 8/28/2023 2:46 PM, Alan G4ZFQ wrote:
On 28/08/2023 17:25, Reinhard Gr?nz via groups.io wrote:My device still has a problem. It does not broadcast in FT8. If I tap the PTT button in the configuration of WSJT-X, it lights up red. There is no signal on the antenna when transmitting.Reinhard, |
Bruce Akhurst
Karl
KK4ITX John