And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate.
Yes, spot on. That, and whether the diode and/or zeners add anything to the receive noise floor. Probably not.? But I need to measure, simulation isn't good enough for me :-D??
I tried to order some 47V zeners but got BZY47. Which is 9.1V. Sent back, and got BZY47 **again**. I should put in a large Digikey order in the next couple of weeks and will add some to it. Here Digikey orders take 10 days and incur a significant expense so you can't do it for a sub $1 order like you can in US.?
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Karl,
I would call these good.? There are only 2 windings on L12.? Both are used on 80, 60, 40, and 30 meters.? The first winding is used for only 20 meters.? The capacitor selection makes the difference between the other bands and 30 meters.
With the above understanding, changes to the 20 meter winding will impact all bands.? Looking across the sweeps, they are close to centered now, and the level is good.? You could make it worse rather than better.
Note,
The LPFs do not affect the receive function unless there is a fault.? They are much higher than the BPF upper limit.? You tweak the LPF toroids to get the best power out.
73
Evan
AC9TU
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Willie,
Simulation FFT says that the commutating diode does no damage to
spectral purity.
This makes sense for two reasons:
1) The current flowing through the diode is small and capacitive until
commutation takes place at the end of a transmission. That is where a
large diode current will flow, but only briefly.
2) The diode current never flows through the primary or the secondary
of the output transformer, and so it never makes it to the LPF.
If you are greatly concerned about spectral purity, consider that
sloppy winding of the output transformer, or parameter imbalances
between the two banks of PA transistors, will do more damage to second
harmonic cancellation and content than the diode can ever do.
JZ KJ4A
toggle quoted message
Show quoted text
On Fri, Aug 25, 2023 at 10:53?AM William Smith <w_smith@...> wrote:
And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate.
73, Willie N1JBJ
On Aug 25, 2023, at 10:38 AM, John Z <jdzbrozek@...> wrote:
?
Dan,
The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible.
Is the inductive spike damaging transistors on QDX?
Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR.
A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash!
JZ KJ4A
On Fri, Aug 25, 2023, 10:12 AM Daniel Walter via groups.io <nm3a@...> wrote:
John,
Your explanation of QDX L14 makes sense. It doesn't seem to be a serious problem for semiconductor failures tho. More of an issue for spectrum 'dirtiness'. The diode would take care of both concerns.
I wonder why it could not be taken care of in the QDX firmware, as it has been with the QMX. There doesn't seem to be the memory and processing constraints of the QCX, even though it doesn't have the capacity of the QMX processor.
--
73, Dan NM3A
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Maybe I could shift some of those BPF and LPF numbers around to get closer to the peaks....
What you think?
I could not have even done this without the stuff Rick sent!
73
Karl
KI4ZUQ
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It works! It receives! I removed the 22pf C403 and here are the results:
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Re: QMX Display Brightness
Rick,
I think he actually means it's too bright. I have changed the limiting
resistor on every QCX-mini and now QMX that I've built. Just too
bright, especially at night. No, I don't have the pin 3 touching the
inductor.
-mike/w1mt
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On Fri, Aug 25, 2023 at 11:20?AM Rick NF6G <rdante@...> wrote:
Dan, take a look at this thread. You may be having the same problem. /g/QRPLabs/message/107812
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Re: QMX Display Brightness
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Re: QMX Display Brightness
Check for contact between pin 3 on the LCD module, and the inductor housing, on the power supply board above it. This will cause the backlight to wash out the display, like you are describing.?
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And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate. ? 73, Willie N1JBJ
toggle quoted message
Show quoted text
On Aug 25, 2023, at 10:38 AM, John Z <jdzbrozek@...> wrote:
? Dan,
The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible.
Is the inductive spike damaging transistors on QDX??
Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR.
A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash!
JZ KJ4A?
John,
Your explanation of QDX L14 makes sense. It doesn't seem to be a serious problem for semiconductor failures tho. More of an issue for spectrum 'dirtiness'. The diode would take care of both concerns.?
I wonder why it could not be taken care of in the QDX firmware, as it has been with the QMX. There doesn't seem to be the memory and processing constraints of the QCX, even though it doesn't have the capacity of the QMX processor. ?
--
73, Dan? NM3A
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Hans & John,
Thanks for the excellent explanation! I'll add the 1N4148 to L14. I can't see that it'll do any harm anyway, and it probably will help.?
--
73, Dan? NM3A
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Hi all. After slooowly assembling my QMX main board, I finally completed mounting all the electrical components. I don't any issue with the potential buck regulator short issue. I measured all tthe LPF and BPF filter caps for accuracy and they were all fine.? I also measured all the toroid inductors as I wound them.? I did find that I sometimes had to remove a turn or two, measuring their value at the frequency it was designed for. This is overkill, but we'll see how the power looks on each band.? I used my Rig Expert AAA-55 zoom for these measurements using the "all parameters" mode. The numbers agreed closely with my cheap LC meter (eBay LC100A or LC200A - I have both).? The Knipex tool worked great on the heavier .33mm wire.? For all the toroids, I stripped the end of the wire before starting the wind so they wouldn't need stripping after the wind.? On L401, when I got to the 19th turn, I used the Knipex tool to strip the wire length needed for the loop, then made the loop.? This greatly eased trying to strip the wire in the loop after completing the wind.
? I would make the following simple suggestions.? If I sound like Captain Obvious, please bear with me.? ?First, it is a good idea to get a PCB holder of some sort if you don't have one, like the Vellman VTHH6-VP for about $16 on Amazon.? I've had one for years and use it a lot.? Second, if you don't have one, get a close cutting wire cutter such as a??Xcelite Weller 170MN for less than $12. It gets you as close as possible to the PCB when cutting off the excess wires. Use this tool only for cutting small wires or component leads and it will last you for a long time.? ?Sure you can get away with any old side-cutter, but it will not get as close to the type listed.? If you don't have good optical inspection tools, invest at least in a 10X jeweler's or watchmaker's loupe which go for about $7.. You can splurge on a set of 5 with different magnifications for about $15.? Inspect as you go along. Don't wait for the end.
But here's the best inspection tool of all, which you likely already have.? Take a photo of the top and bottom of the PCB with your smartphone with highest size available.? You can them look very carefully at the photo with app that comes with your operating system like Paint in the Windows OS. Zoom in, and you can get great quality, high magnification with this tool you already have. Use good lighting when you take the photo and avoid blocking the light with your body.? Perhaps a friend or your better half can shine a flashlight on it if necessary.? I like to add little red circles around suspect joints in the photo to mark on the photo where I have to look and possibly touch up.? The top of the main board had no issues.? The bottom or hand-soldering side of the board had about 8 potential issues, including a small solder ball between two adjacent pins of the processor, solder bridges, and unsoldered pins.? The USB connector had an unsoldered pin in the upper left corner.? ?Also inspect with your naked eyes, which might pick up something when light hits it differently that when the photo was taken.
Inspect, inspect, and inspect!? Don't gloss over or rush this important step (I know I know you are anxious to finish it and watch the grand powerup!)? But trust me, a pound of careful inspection is worth 100 pounds of letting the smoke out.? Good luck with your builds.
-Steve K1RF
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Re: No Sound Card digital modes
Yep, that would certainly make sense, and has been mentioned before. However, it would require a fairly major revision to wsjtx, and since it works as is (even if it’s not technically the most efficient), they are unlikely to put in the work to “fix“ the problem. 73, Willie N1JBJ
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On Aug 25, 2023, at 10:38 AM, KI7MWA via groups.io <entilleser@...> wrote:
?Suppose that WSJT-X could be modified to side-step the whole 'translate the desired rf frequency to an audio tone, send the tone out on an audio cable to the radio, where the tone is mixed in on the baseband carrier, after which the carrier and all the intermodulation artifacts are filtered out', and simply send the required rf frequency (the baseband plus tone) to the radio.? The QDX could side-step the sound card and generate the appropriate rf frequency directly (rather than detecting the appropriate frequency by means of the sound card, and then generating the frequency directly).
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Re: FS: QCX "Classic" 40 meters
QCX 40 has been sold.
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73/72,
Dean K5DH
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No Sound Card digital modes
Suppose that WSJT-X could be modified to side-step the whole 'translate the desired rf frequency to an audio tone, send the tone out on an audio cable to the radio, where the tone is mixed in on the baseband carrier, after which the carrier and all the intermodulation artifacts are filtered out', and simply send the required rf frequency (the baseband plus tone) to the radio.? The QDX could side-step the sound card and generate the appropriate rf frequency directly (rather than detecting the appropriate frequency by means of the sound card, and then generating the frequency directly).
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Dan,
The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible.
Is the inductive spike damaging transistors on QDX??
Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR.
A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash!
JZ KJ4A?
John,
Your explanation of QDX L14 makes sense. It doesn't seem to be a serious problem for semiconductor failures tho. More of an issue for spectrum 'dirtiness'. The diode would take care of both concerns.?
I wonder why it could not be taken care of in the QDX firmware, as it has been with the QMX. There doesn't seem to be the memory and processing constraints of the QCX, even though it doesn't have the capacity of the QMX processor. ?
--
73, Dan? NM3A
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Karl