Re: QMX build troubleshooting
I built it for 12v and I had the PSU at 10-11v.
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Re: QMX build troubleshooting
How much voltage, EXACTLY were you using to power the radio?
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Hello Richard
My original aim for the QDX-M was to make versions for 160, 630 and 2200m, which are not suitable for the QDX because of the difficulties with PIN diode switching such low frequencies. However I got sidetracked by many other projects which is why I still did not go through the process of building and documenting one for each band. So at the moment it would be an experimental thing for you. The filters will not differ much from the 80m filter in the QDX 80-20m version, and this would provide a good starting point. The firmware only needs adjustment of the Band Configuration screen for the desired band.?
On Wed, Apr 23, 2025 at 2:39?AM Richard Katsch via <rkatsch= [email protected]> wrote: Hi All,
I have a plan to build a QDX-M for 80 metre FSQ activities. The QDX-M appears to be ideal for this with it's clever non SSB method of producing the tones required. However, the web page shop only lists 10,11,12 metre bands at the moment. After looking at the circuits for the QDX and QDX-M the changes for 80 metres would seem to be:
1. Use the low pass filter design for 80 m from the QDX. i.e change the inductors and capacitors in the QDX-M to be the same as the 80 m filter in the QDX.
2. Change the inductor in the QDX-M (L12) so that it resonates with the 56 pF capacitor at 3.6 MHz.
3. It looks like L14 remains the same for all bands.
So my question is: Has anyone done this and are there any steps I've missed, and can I buy a QDX-M kit with all the appropriate toroids, inductors, and capacitors? I'd like to buy one QDX-M for 80 metres and one extra set of components to change the unbuilt 10 metre QDX-M I have to 80 metres.
Apologies for the long and involved post.
Best Regards
Richard Katsch VK2EIK
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Re: QMX build troubleshooting
In firmware update mode only the linear 3.3v regulator is being used, there is no 5v rail and the buck converter regulators are not being used. See this article in the wiki for start up process.
?
It is possible that you have a short on the 5v rail. ?There is a test process for the plug in buck converters in the wiki. ?Check the board for shorts on the voltage rails without the plug in converters connected and proceed from there.?
73 Nick G0OQK
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Re: QMX build troubleshooting
On Wed, Apr 23, 2025 at 04:52 AM, <f4jvu@...> wrote:
tried to start the radio by pressing the left encoder
Sounds like the short happened when pressing the encoder. Start looking there. The clearances are incredibly tight in the QMX, and it's a reasonable place to start.
Beyond that, I can't begin to suggest how to determine what was damaged by the high current draw.
?
--
72 de N4REE, Bob Easton - QRP CW forever
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Re: Newly assembled QMX, SWR=1.5 with dummy load
Thanks Jerry,
I had a load of 2W 51R SMD resistors so using 4 in a series parallel arrangement gave me 8W power handling.
?
Another way to do the power calculation is Vpk * Vpk / 100, that's practically mental arithmetic, or if you have a scope that measures the peak to peak voltage Vpp * Vpp / 400.
?
This simple little dummy load come peak V measurement come attenuator was the best thing I made to help with testing a QMX.
?
Incidentally the 2K5 resistor is 1k0 + 1k5.
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QMX build troubleshooting
Hello,
?
I completed building the QMX yesterday. The initial plug in went smooth, no smoke no current draw.
I booted the QMX into update mode, put the firmware on it no problems at all.
Then I removed and re-inserted the dc plug and tried to start the radio by pressing the left encoder, suddenly I saw big current draw (stupidly i forgot to limit my power supply) it went up to something like 7 amps, so I unplugged it immediately. I dint see any smoke but the device did get hot in some areas. Visually I do not see anything burned on any of the PCB.
?
So now, when I plug the radio in the DC plug nothing happens until I press the left encoder which creates a short and puts the power supply into constant current mode. (This time limited...)
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Can anyone please advise for any troubleshooting steps?
I put some pictures of the boards in attachment.
Thank you.
?
?
?
?
?
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Re: QMX only hearing static
It may be irrelevant to your case but something similar on another QRP labs receiver was recently traced to the MS5351 emitting narrow band noise instead ?of a single tone ?carrier on receive LO frequencies which resulted in loud static in the speaker
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Try to listen to the MS5351 receive output signal on another CW/SSB receiver. ? If you have signal strength but no CW tone that¡¯s the issue ?
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I have recently seen unstable 1pps on my QLG2, used for a GPSDO
The QLG2 has a minimum of 10 fixes, tracking 17 vehicles and signal strength
35 - 40 on an external mushroom aerial.
The 1pps suddenly jumps to a slightly shorter perid than 1s that throws the
PSDO into holdover.
Has anyone else seen this behaviour? Is it a duff GPS engine. Could it be a
software glitch in the QLG2 ?
Ideas on a $5 bill :-)
73 Mike
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Hello, I've just joined the forum and was ploughing through the 100+ emails I've received
while waiting for my QMX+ to arrive..
Randy
? I think it might help to explain how this thing is meant to work. So here's my shot at it:
? When it's powered up and the processor turns Q109 on for the first time there is no current
flowing through L102, and being an inductor it tries to keep it that way, but of course
doesn't succeed. So the current increases, causing C106 to charge up and some current to
flow through R114 and Q110, via "gnd" and back to the power supply.
? When the voltage across C106 reaches the required value the processor turns off Q109. At
this point L102 doesn't want the current to change so it supplies the current from its
stored energy (remember I squared L). If we think in terms of conventional current, flowing
from positive to negative, then the current flows out of the RHS of L102, through R114 and
Q110, along the gnd wire and back up D107 to the LHS end of L102. While it is doing this
D107 is forward biased and so with its anode connected to ground the cathode should be at
MINUS 0.6v approx.
? The fact that the D107/L102 junction is not swinging negative suggests that either
there is no circuit around the components described above, and hence no current through
L102, or that L102 is not storing the magnetic energy, either because its got a duff
core or a shorted turn.
? As an aside I see from the cct diagram that C106 is only rated at 10V so the voltages
you show are pushing it to its full rating.
? Good luck with it.
? Keith, G0GNL
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On 22/04/2025 23:39, Richard Katsch via groups.io wrote: I have a plan to build a QDX-M for 80 metre FSQ activities. The QDX-M appears to be ideal for this with it's clever non SSB method of producing the tones required. However, the web page shop only lists 10,11,12 metre bands at the moment. After looking at the circuits for the QDX and QDX-M the changes for 80 metres would seem to be:
1. Use the low pass filter design for 80 m from the QDX. Richard, The QDX-M has not featured much in this group. I guess it is for more specialised users, the QDM came out soon after and little has been added to the QDX pages. I bought one because the diode switching is omitted, theoretically giving a little more gain on high frequencies, and the possibility of use at LF. I'd think the standard QDX is better for general use being multiband and band variations better documented. You could miss out some unwanted bands. The QDM LPF will not be much different than the QDX ones but maybe the RX filters will vary. The multiband QDX RX filters are adjusted because of stray capacitances and other interactions. 73 Alan G4ZFQ
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Re: Another good solar description
Thanks Ed for your document. Helping to understand the sun effect on our hobby. ?
73, Ben?
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Re: CW Practice / Rag Chew
Thanks Ed, John for documents. That¡¯s help me to begin to understand the sun effect.?
Jean-Jacques, could you re-post as I don¡¯t find your link ?
Thanks again for help.?
73, Ben?
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Re: QMX+ no power output, low SMPS bias current
One of my bnc adapters to my dummy load recently failed,? too, and was very flaky.? Not an uncommon problem.
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For the power output, do LPF scans and see how they are responding.? The efficiency of the T501 windings can also affect power out on the higher bands.?
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Stan KC7XE?
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Re: QMX+ with WA3TFS amplifier
Jim:
?
Excellent work and yes, surgery went well but there will be some rehab involved - I¡¯m really sore right now. Right now, I can¡¯t get up the stairs where the shack/bench is located. But, it¡¯ll still be there. Your solution will work great for the QMX with wired PTT. But what if I decide to use say, a FT-818 that might use RF detection ? I might need a closure of that circuit when there is no TRS plug.
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Just food for thought ¡ which right now, I admit, mine isn¡¯t very clear right now. ?
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73, Jamie
WB4YDL
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Re: QMX+ no power output, low SMPS bias current
I rewound T507 and got pretty much the same results, until I checked the BNC connector on my dummy load, and discovered it had been damaged and wasn't giving a consistent connection.? I pulled out my bigger dummy load and put a BNC adapter on it, and was able to get the following values:
| Band (m) |
Reported W |
| 160 |
5.9 |
| 80 |
4.9 |
| 60 |
4.2 |
| 40 |
3.3 |
| 30 |
4.1 |
| 20 |
2.2 |
| 17 |
4.5 |
| 15 |
1.9 |
| 12 |
1.7 |
| 10 |
2.4 |
| 6 |
1.4 |
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So it seems like I'm almost there.? I just need to figure out why my power is so low on 6, 10, 12, 15, 20 and maybe 40 meters.
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Hi All,
I have a plan to build a QDX-M for 80 metre FSQ activities. The QDX-M appears to be ideal for this with it's clever non SSB method of producing the tones required. However, the web page shop only lists 10,11,12 metre bands at the moment. After looking at the circuits for the QDX and QDX-M the changes for 80 metres would seem to be:
1. Use the low pass filter design for 80 m from the QDX. i.e change the inductors and capacitors in the QDX-M to be the same as the 80 m filter in the QDX.
2. Change the inductor in the QDX-M (L12) so that it resonates with the 56 pF capacitor at 3.6 MHz.
3. It looks like L14 remains the same for all bands.
So my question is: Has anyone done this and are there any steps I've missed, and can I buy a QDX-M kit with all the appropriate toroids, inductors, and capacitors? I'd like to buy one QDX-M for 80 metres and one extra set of components to change the unbuilt 10 metre QDX-M I have to 80 metres.
Apologies for the long and involved post.
Best Regards
Richard Katsch VK2EIK
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Stan and Ludwig:
1)? Some conflicting information to clarify/resolve: in one place you say "ADC_3V3 measures 6.6V" and another you say you measure 3.3V at ADC_3V3 (which corresponds with the 6.6V seen in the diag screen).? But you also say that Q111 source is cleanly at 10.6V.?? This doesn't quite add up: if Q111 source is at 10.6V, then ADC_3V3 must be at 5.3V (not 6.6 or 3.3), because of the resistor divider of R110 and R112.? So something is still wrong with this measurement picture, or something is interfering.
Ah, yes, confusing. Actual measured is 3.3v at ADC 3V3. Which as you mentioned Indicates an actual VDD voltage of 6.6. But as I noticed also, the diag screen says 5.3. So no, actuals and calculated values do not add up. I also thought that 10.6 should show up as 5.3 at ADC 3V3. Maybe it is confused by the VDD actual measured being 2.97 (sourced by IC101) and ADC 3V3 being 3.3 measured indicating a VDD of 6.6v. Hopefully I didn't make it more confusing. Suffice to say. I agree...
?
2) And since the voltage at Q109 Drain is not going down to 0V, it is not getting fully turned off, or it could be damaged.? I would check the voltage waveform at Q109 gate. ?R107/Q113 should be pulling the Q109 gate up to very near its source voltage when PWM_3V3 is low, which should turn off Q109. ?If this is happening, then Q109 is probably broken.? If the gate voltage is not getting that high (which I suspect is the case) then another of the PWM components isn't doing its job.? Check to make sure PWM_3V3 looks like a good pulse wave from 0V to almost 3V, and check the Q107 drain and Q113 emitter voltage waveforms to diagnose where the problem is.?
Right. On the Schem. I show the waveform at Q109 gate / Q113s emitter. It is ramping up to 12v and back all the way down to 0v, hold for a bit and repeating.
The waveform on PWM 3V3 is perfect, Q107 drain is a clean square/rectangle wave duty cycle matching the gate.
?
Ludwig
Randy, something is strange. Early you wrote VDD is produced by the linear regulator. LIN_REG_EN must show some volts to connect IC101 to "+12V" via Q102. Your schematic shows 0V at LIN_REG_EN. Appropriate Diagnostics show the status SMPS. This should switch off IC101. So there maybe a (helpful) failure.
Yes. Because I lifted Q111 and D109 it has to be coming from the linear regulator. Why it is on when LIN_REG_EN is at 0v I do not know. Maybe Q102 is shorted.
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LIN_REG_EN at 0V would also switch off Q110 and R114. R114 is an artificial load to operate the SMPS without a real load. It's hard to adjust a SMPS with (nearly) no load. Maybe this is the reason for the too high voltage at D of Q109.
That is what I suspected. Drain floating in the breeze.
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A not well working Q113 may cause a similar effect. Please check the oscillogram at B of Q113. It should show rectangle from around 0V up to "+12V". The voltage at E of Q113 should follow but with around 0.7V at low and "+12V"-0.5V at high.
Nice square (rectangle) wave on the base of Q113. The wave form on the emitter is equivalent to what I see on the 5v circuit. It is shown on my schematic. Different duty cycle.
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Thanks for all of the input. I have a full complement of replacement components arriving on Thursday. We will soon find out who the culprit is.
My money is on D109 at a minimum since it won't power up at all when it is in-circuit.?
--
Randy, N4OPI
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Re: FT8CN Getting it to Work!
Thanks for sharing these details, John! How clumsy is it to operate via a phone screen? Workable for a POTA/SOTA event?
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-Nate
N8BTR
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I did not go mobile, but rather made a recording of the audio on my ICOM transceiver. These were my final settings after trying various settings on my QMX with the Heil Pro 7 (IC)headset. I worked a couple of POTA stations who said my audio was clear, just weak. I left some heading words out but I think you will get the idea. Hope this is helpful.
?
EQ
?On
?Global -17
?300
?+2
?.5
?3000
?0
?.9
?
AGC
?On
?10
?10
?2
?
RX filter
?2500
?
TX filter
?2700
?
Mic gain
?63
Comp
?3
?
Noise Red
?On
?
Noise Gate
?On
?Thresh 50
?99
?Att 10
?
Vox
?On
?Thresh 35
?Hold 6
?
Drive 900
?
CESSB On
?
Phase PD On
?
?
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N4REE - Bob
Bruce Akhurst
Mike