Thanks for the feedback, Chris!

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On Mon, Jan 27, 2025 at 08:47 AM, G0IMX wrote:

Also might look at L12 again as I used the group recommended T50-6 with 10t - the turns are squeezed onto half of the toroid for best peak of the Putty rf filter test.

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Does that mean it was peaking too low, otherwise? Wondering if 9 turns, or a smaller capacitor value should be considered for the BPF....

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-Nate?

N8BTR

I think you are right.? From the middle of the first paragraph:

"The input signal to the PA is phase modulated with constant amplitude. The amplitude modulation is added at the output by varying the gain of the PA."

It's safe to assume they are synthesizing the amplitude and phase information digitally.

They detect the phase and amplitude at the output of the final, feed that information back to the algorithm.

The paper was written in 2004.

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The technology that goes into a cell phone sold for $30 at a local drug store is amazing.?

Hard to duplicate at a reasonable cost if you aren't building millions of them.

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Jerry, KE7ER

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On Mon, Jan 27, 2025 at 12:41 PM, DD4WH wrote:

This has happened twice now....after moving the powered up QMX+ a short distance across the bench, I smelt the unmistakable whiff of electronics getting way too hot...I don't have the QMX upper case fitted as I'm often doing something inside the rig.

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As I don't have the QMX upper case fitted, I also saw a wisp of smoke coming from the PSU area of the PCB, I immediately disconnected the power supply...the inductor on the 5v board was red hot.

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After everything has cooled down I connected the power supply again and the rig would power up in the normal way...everything working as before.

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Reading about sudden breaks in the power supply causing problems I thought I would look at my setup using the continuity test on my DVM, I confirmed the power supply plug was a 2.1mm variant, but wiggling the plug showed an intermittent connection on the +12v connector, I soldered the riveted centre pin to the socket's tag, this made no difference.?

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It appears that all 2.1mm connectors are not created equal, changing the suspect plug sorted the problem out.

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I have always wondered about the security of connection of these connectors....there is no spring involved in the centre conductor, it just seems to rely on it fitting where it touches, perhaps the spring on the outer of the plug pushes the plug sideways to gain some sort of contact between the inner of the plug and the socket centre pin, still not ideal.?

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I have seen leads fitted with plugs which appear to have a two prong sprung fork to grip the center pin of the socket (laptop power supplies) but invariably these are moulded onto the cable, I haven't seen them available as free plugs.

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So, if you've been having problems such as above, I hope you have been able to remove power before before permanent damage is caused...having the lid off during normal operation saved my QMX+.

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Maybe wise to check the continuity of your power plug and the QMX+ while manipulating the connection, even if you do have a 2.1mm plug fitted.

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73 Steve G4EDG

That paper actually describes the general category of digital pre-distortion, which is a method of linearizing a high power amplifier stage. This allows using lower cost output amplifiers or pushing them a bit into their non-linear region while allowing them to perform much closer to the performance of an ideal linear amplifier.? It is commonly used in the cellphone industry, and high end chips and/or custom FPGA designs are used to perform this function. There it is needed to reduce undesired intermodulation products when handling multiple low level RF input signals simultaneously.? They make use of "pre-distorting" the RF waveform to cancel out the distortions inherent in the high power output stage. The "pre-distortions" make use of both amplitude pre-distortion and phase pre-distortion.? Don't ask me how I know. In the ham radio world, digital pre-distortion is used in some high-end rigs like the Apache Labs,? Flex radios, and Icom IC7610.? The original ham radio implementation was called Pure Signal, developed in the Open HPSDR group by by Warren Pratt, NR0V, who received the 2014 ARRL Technical Innovation Award for this innovation.? This is not used for SSB generation at all, but for linearization of the amplifier chain to reduce intermodulation products in SSB.? The QRP labs SSB implementation incorporates a method of digital predistortion which is part of the SSB generation process itself at low cost and high performance.?

-Steve K1RF

A square inch piece of fine sandpaper to finish cleaning off the magnet wire enamel.

Interesting.? Very strange.

So this is not a save-config issue.?

It is an issue with how fldigi interacts with your Win11 and USB connection - causing fldigi to disable the port audio when it gets this error.? Since you had it working for a time, it may be something flaky in the USB connection.? If you are using a USB-C port on the computer, use instead a USB-A port (with a good A to C cable).? If you are using a high-speed USB port or a USB-hub, switch to a different port.? These things go through different driver chains in Win11 and sometimes can cause problems.? Or maybe just a different USB cable, perhaps with clamp-on ferrites.

Good luck -

Stan KC7XE

A while ago I read about a faulty barrel connector (the part at the PCB).

Tom, if your power connector was the right size, it is very unlikely that the damage is being caused by the PSU or the cable (unless the PSU is erratic, which is not likely - what kind of PSU are you using?).

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QMX is not that sensitive to power interruptions (at least with current hardware and firmware revisions).? I have tried to break one of mine here that I have for testing (trying to see where the reported weakness is), and I can't do it.?

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It is more likely that something internally is shorting when you move QMX, due to the very tight tolerances inside.? I would check carefully (with good light and magnification) the various parts of the 'sandwich': between the Display board and main board there is sometimes very little clearance between the soldered-in 16 display connector wires and the items below, and that display 'tab' that needs to be bent over sometimes needs more bending, to not make contact with the PSUs below.? Another item is clearance between the back tab of the power-in connector and the encoder body. Or some other contact somewhere.? Was your kit a v1?? There were some potential assembly issues (that could cause shorts) on v1 that got resolved in later versions.? One was a via or solder pad too close to the edge of the board, one was component spacing on the PSUs (but you got new ones), and another was spacing behind the power-in connector.? There may have been others that I don't remember.?

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Stan KC7XE

Stan, yes I first attach USB then turn on QDX then start fldigi and flrig. I still have this Portaudio unchecked with the following message:

"Could not open audio device: PortAudio error: Unanticipated host error Check for h/w connection and restart fldigi"

73 - Pierre - FK8IH

There is a web page,?, which will open a serial terminal session.? It should work on any Chrome based browser on any desktop system: Linux, Windows, MacOS, or ChromeOs.

Do you first attach USB and then turn on QDX BEFORE starting fldigi?

If you start fldigi first, the QDX audio devices are not present, so it can't find the port audio you saved.

Stan KC7XE

This is my Flrig and Fldigi window.

did a lot FT8 and FT4 last weeks without any issues..... the QMX is the greatest very little rig ever .... for sure in cw too because of the great filters.... really a dream....

thanks Hans and team for a wonderful rig ...

keep going on?

Thanks again Oleh, it works nearly well now with the right RX level attenuator set to ZERO. I had searched in the manuals (more than 1,000 pages!) of Fldigi and could not imagine that to have full audio the slider was to be set to its minimum. Well, using Flrig my computer works well with my QDX and it transmits RTTY.

I still have one problem: each time I start Fldigi I have to check Portaudio in order to have Capture and Playback QDX. Then I click on the Save button then the Close button and I open the Configure button on top of Fldigi window and click on Save Config but it does not work, next time I open Fldigi I must do it again. What is amazing is that yesterday during my first trials of Fldigi this Save Config worked well and now it does not work anymore!!!

Anyway I'm happy to have more capabilities for my wonderful QDX (high band 30-20-17-15-12-10M).

73 - Pierre - FK8IH

Hi,

Thank you all for your answers!

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Regards,

Lionel F4IZN

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P.-S. The HM102 has been modified so that the range is now 20 W, instead of 200 W, to easily read QRP power levels.

Allright, I've checked my connector, it's a 2.1mm. I'll check what is fried on the psu boards with the help of this wiki page : /g/QRPLabs/wiki/37128
I hope I didn't break anything beyond the psu boards, well... I'll see.?
Honestly, if it's the case I may give up on this project. I've bought two units in kit, I got one for a friend but I'll keep it on the shelf until I've fixed this issue.

I'll be really happy to have this rig running but it's no fun to get a rig that can instantly go qrt if you wiggle the power cord too much.

I'll report back on how it goes.

I often use TeraTerm instead of PuTTY, for some people it is more intuitive.

It is a free download for Windows.

Remember in either of these, that you don't need to set up SSH or TCP/IP options for use with QMX.

You only need to select and setup the proper Serial Port - the baud rate/data bits/parity/stop bits are not important, but the "flow control" should be set to "none". (QMX USB uses a virtual serial port, called COM ports in Windows).

Stan KC7XE

hi, PuTTY is mostly self explained... I was using it since around a year now without any knowledge about terminal since then ...

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vy 73 de Udo DF4BJ?

I may have misunderstood this technically, but I think this principle is frequently used in professional mobile transmitters, eg. cell phones. However, the name used is also different, it's often called polar transmitter or polar coordinates transmitter. I think, most recent cell phones use polar transmitters, but I may be wrong. At least, some papers seem to point in this direction:?

So, maybe we do not need another new name for this principle?