I just used an inexpensive MAX9814 Arduino mic amplifier module, which I also happen to have in my junk box.
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Cheers.
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Mel. M0KMD.
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Re: CW Practice / Rag Chew
I wouldn't describe a K of 5 as good. A figure of 1 or 2 is much better. The lower bands eg 40m may be very difficult to use at a K of 5. Digital will stand the best chance of getting through on these bands. The SFI is an indication of how well you can get DX as a higher number helps the signal to skip multiple times especially on the higher bands eg 10m. The A figure you can ignore as it is showing what's happened in the past. The SSN figure is a measure of sun spots and closely follows the SFI figure.
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The above is a brief over-simplification but might help.?
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Re: QMX+ Died on the Operating Table?
Probably time to inspect the connections you made closely for stray solder and/or lifted track?
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Very good Mel!
I think a mic preamp perhaps on a daughter board with special consideration to low noise components, good equalization, layout and filters, and a low impedance output to feed the QMX A/D converter would be an excellent addition to the QMX. Depending on the dynamic range of the A/D converter and a higher input signal, one might not need the spur removal with the internal mic and second A/D converter.
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I have some small mic preamp boards, and designed a discrete one for a dynamic mic I had. I will ?have to give it a try if the Pro 7 doesn¡¯t work well.
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The headset has a electret mic. I didn't measure the resistance. It sounded perfectly adequate when I used it on my pc.
Hower, the output from the mic seems too low using it with my QMX+.
I did try two other electret capsules I had in my junk box, they were marginal improvement over the headset mic.
The headset works great with the mic preamp, however.?
The mic gain is set to 35 and compression set to 3, produces good results on my QMX.
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Re: Release of version 1.2 of ABS solution for QMX+ (Automatic internal antenna tuner, internal battery and internal speaker with audio amp)
#ABS
#ATU
#PSU
#QMXplus
I'd be interested in a group buy if and when it happens.
QRZ is accurate for me.
Glenn
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Mel, was the gaming headset mic an electret element, or another type like dynamic or crystal elememt? What does its resistance measure?
Gaming headsets are known to be poor quality in general. In my mobile IC-7100, I used a headset with mic but from a well known reputable company and with an electret mic. It worked great for the 7100.
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QMX+ Died on the Operating Table?
I started having problems with my QMX+ ver 1 after the SSB calibration.? I ended up replacing the BS170s in the final amp which got me back to full power.? However, I noticed that the power was not reducing in SWR test mode like it should.? I determined that the power modulation transistor Q507 had probably failed.
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I replaced Q507 with a new transistor, but the QMX+ did not survive the operation.? I am now unable to get the QMX+ to power up.? I suspect that I damaged the board when I removed the old transistor and now have a short to ground on the board under the transistor.
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Is there hope of bringing this QMX+ back to life, or is it time for a new main board?
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--
Steve KA0SM
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FT8CN Getting it to Work!
I installed FT8CN to an Android phone but found it sometimes transmitted and often did not.?
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Then I discovered there is a magic button on the screen which turns on transmission! It is in the top right of the Calling screen and looks like a loudspeaker. You need to click on this until it turns red as shown on the screen shot. I also discovered by repeatedly clicking this button it changes the "Sequential" setting between 0 and 1 which changes whether it transmits in the first or second time slot.
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I have read the English manual but don't remember seeing these controls.?
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The settings are QDX rig selected which works with my QMX and CAT control. Everything else is default. Phone is a Google Pixel 9a.
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Ok, good new information always helps.? Looks like the processor is indeed able to measure the voltage at ADC_3V3, but I am quite confused about why the processor would be maxing out its 3V duty cycle at 27% when the voltage is higher than 3V - it seems that it should be reducing the duty cycle to reduce the voltage -- but the processor is probably confused, since its own VDD is at 2.97V (from the linear regulator), and isn't changing.? Because you have the drain of Q111 lifted, VDD and the ADC_3V3 voltages don't track.
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The data you present gives two other issues to resolve, before restoring the drain of Q111:
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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.
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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.?
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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.
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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 to high voltage at D of Q109.
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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.
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73 Ludwig
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Re: QMX only hearing static
Kai,
I guess Jeff will help. After repair it would be nice to read, what he found.
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73 Ludwig
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Re: QMX only hearing static
Ludwig,
I do not have the ability to use a variable power supply, so I did not test as you wrote earlier. I am going to reach out to Jeff Moore and see if he's willing to help fix it as I do not have the ability to replace SMD parts.
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Thank you,
Kai Bouwman
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Re: Power out on 60 mtr QCX+
Keith, I don't think you needed to take any turns off L1 or L2. Yes, please watch the video Evan suggests. Hans shows his technique for doing the adjustments without cleaning holes in there as well.?
Now, if you do all that and still have low power, I would suggest looking at the capacitors c25, 26, 27 & 28 to make sure they are the correct values. And the same goes for C30. Also recount the turns on L1,2,3&4. Spread the turns on L4 if you didn't already do so. And as you suggested carefully inspect the soldering of all those components, especially the enamel removal from the wires. If you see enamelled wire sticking through a solder blob it is likely it needs more heat. That takes some close viewing with a jeweler's loupe or some other magnifier.?
Ron
Hi Keith,
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Have you tried any of the suggestions on the QCX troubleshooting page?
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There is also a YouTube video by Hans on the QCX:
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73
Evan
AC9TU
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Thank you Hans for responding. I will try Stan¡¯s solution for now.
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>?Also, best not to re-use chip resistors and caps after taking them off the board . . .
If you are going to save the part, just clip the leads and unsolder the part one lead at a time.?
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Thanks Stan. Let me clarify a couple points.
Source on Q111 = 10.6vdc. With a scope I see a PWM'd square wave from +11.9 to +10. Not returning to 0. My suspicion is that this is due to the Q111 drain floating.?
Correction of my statement: At the drain of Q109 is the PWM'd square wave that alternates between 11.9 and 10v. On the other side of the filter at the source of Q111 we have clean 10.6 DC.
Where-as in the 5v circuit, the output of Q108 is alternating between 11.9 and 0 volts. And is being filtered to clean 5v DC at VCC.
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No.? L102 and C106 filter the voltage, trying to average it, so it won't go down to zero.
Correct. And the filter is working as I would expect. Filtering an alternating 11.9 to 10.0 28% PWM'd square wave to 10.6v of clean DC because it is oscillating between 11.9 and 10v not 11.9 and 0. Obviously not the voltage we want.
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The processor measures this voltage, actually half this voltage, at the ADC_3V3 connection.?
Ok, so that explains why the diagnostic screen shows 6.6v where I'm measuring 3.3 at ADC 3V3. ADC 5V measures correctly at 2.5v.
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Since you see 10.6V ave, the processor's measurement of the ADC_3V3 voltage is likely not working.?? If the processor can't see the voltage on ADC_3V3, it will continue to increase the PWM percentage to try and get it there, giving a too-high voltage.? This causes D109 (when present) to conduct and keep the voltage near 3.3V, and possibly burning it out.? So check carefully to make sure R110 and R112 are in place, and measure the voltage at the ADC_3V3 junction, which should show VDD/2.? Also inspect to and make sure the processor pin where ADC_3V3 is received isn't shorted to something (solder flake, etc.).
R110 and R112 are in place and measure 27k each, in circuit.
ADC 3V3 measures 6.6v.
I used my Super loupe to inspect all of the processors legs and they are clean as a whistle.
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If the above failure is happening, and you bring up the diagnostics page in the terminal program, you would likely see the 3V in 'linear' mode, and the 3V 'duty cycle' equal to 'duty max', which means the processor is trying hard to get the 3.3V smps working but not seeing the result.
They say a picture is worth a thousand words, so please see the attached diags screen and my notes on the schematic incl waveforms at G and D of Q108 and Q109.
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Thanks again Stan!
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Randy, N4OPI
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Re: Newly assembled QMX, SWR=1.5 with dummy load
If you are worried about series inductance of resistors, best to build a 50 ohm dummy load
of all parallel resistors.? ?Not a series combination of two sets of two 50 ohm resistors in parallel.
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Jerry, KE7ER
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On Tue, Apr 22, 2025 at 07:00 AM, Jerry Gaffke wrote:
Adding Chris's BAT41 and 0.1uF cap to read the peak voltage with a DVM is a good idea, will work great for a QMX.
Han's 20W dummy load does the same, but uses a 1n4004 diode, good for 400 Volts, assembly instructions have the schematic.
The BAT41 is a shottky diode so will be more accurate, but 20W would be close to blowing through it's 100 Volt max spec.
The DVM will see the peak RF voltage from ground, so multiply by 0.707 to get Vrms (the rms voltage of your transmitted signal).
The power out in Watts is then equal to Vrms*Vrms/50, and that should be fairly accurate assuming the RF is a sine wave.
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Chris has two 100 ohm resistors in parallel to form the 50 ohm on the source end of the coax that goes to
some measuring device such as a tinySA, which we assume has an internal 50 ohm termination resistor.
So his circuit is the same as what I was suggesting for the 50 dB attenuator
His 2.5k resistor is very close to the ideal value of 2475 ohms that I had calculated.
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At 10 Watts out into 50 ohms, the voltage across the 50 ohms is sqrt(10*50) = 22.4 Vrms.
And the voltage across Chris's two 100 ohm parallel resistors is? ?22.4v/(2500+50) * 50 = 0.44 Vrms.
Power dissipated by that 50 ohms is? 0.44*0.44/50 = 0.004 Watts.
Even ridiculously small 0402 (imperial size) chip resistors are rated for 0.062 Watts.
Two 100 ohm resistors in parallel present half the inductance so will be more accurate at 50 MHz,
but if using a surface mount chip resistor that shouldn't matter much.
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Jerry, KE7ER
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?This might need clarification for some:
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>> Lifting one end is a good way to lift the opposite pad.?
> Donald, you are right. It's good to tell this.
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Lifting one end of a resistor or cap or diode can rip the opposite pad off the board.
That will ruin your day.
Usually easy enough to repair by running a wire from one end of the new part to some nearby pin, but not always.
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I find it much better to use two irons, one on each end of the part.
A SOT23-3 part is easy enough to bend pins on without ripping up pads.
Anything bigger, and I use chip quik alloy applied with a soldering iron to each pin, then a hot air gun,
then very gently pick up the part once it is totally free.
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Also, best not to re-use chip resistors and caps after taking them off the board.
The bits of metal at the ends might still be connected physically,
but the heat and mechanical abuse can separate that metal electrically from the internals of the device.
Keep a stock handy of replacement parts, they only cost a penny or two each.
If you do have to reuse such a part, make sure the metal bits are still solidly attached,
and check the part with a meter for correct value.
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Jerry, KE7ER
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On Tue, Apr 22, 2025 at 07:20 AM, @Ludwig_DH8WN wrote:
On Tue, Apr 22, 2025 at 04:09 AM, Donald S Brant Jr wrote:
Lifting one end is a good way to lift the opposite pad.?
Donald, you are right. It#s good to tell this.
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I'm doing this only for some SMT packages e.g. small diodes (SOD323), small transistors (SOT23) and some tantalum capacitors (yellow). All of these have tiny metal stripes as contacts. There is a distance between the place the stripe comes out of the plastic case and the solder joint. There the metal stripe could be bend with nearly no force. I would never try this for packages like SOD80 or TO252.
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73 Ludwig
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Re: QMX only hearing static
On Mon, Apr 21, 2025 at 10:23 PM, @Ludwig_DH8WN wrote:
and never saw a broken IC403.
I have to correct. Checking my repair records I found one case with a broken IC403, not clear why broken.
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73 Ludwig
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John Laidler
Bruce Akhurst
Ronald Taylor
