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Severe QMX+ audio distortion

 

I've been annoyed by the audio quality of some earlier kits, so I asked a friend, an expert builder, to borrow his newly completed QMX+ for a listen. The results are quite bad. Attached are several recordings taken with Audacity from the earphone jack. Also attached is a spectral snapshot of a portion of the SSB recording --- notice the distorted envelope. Also notice the high hiss content of both modes and the 'fur' (phase distortion) on the CW filter. Not good. I think I'll pass on this kit.
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Chuck w8mqw
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P.S. There's the chance that my data is flawed. I would be delighted to be disabused of these awful results.
 

I think something is wrong with this QMX+. Could you check audio connecting Audacity via USB?
And could you show screenshots from Terminal - Test ADC I/Q for some Bands?
73 Ludwig
 

That is not my experience with the QMX/QMX+ audio.
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When I use a reasonable quality earphone (I have some very old Apple iPhone earbuds with the 3.5mm plug), or when I use my Heil headset, the quality of the audio from my QMX audio jack is excellent.? Surprisingly so.? It is quiet and clear, with no discernible distortion, SSB or CW or digital modes.? Even a cheap pair of earphones I bought before boarding an airline flight produce very nice audio.? I would say it is exceptionally good, considering the low cost of this kit.??
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When I hook up a cheap powered external speaker, the audio is good, but not nearly as good, and easily distorts at higher volumes.? I understand from others that they have external powered speakers that work very well.
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The QMX audio output is designed for earphones/headphones.? Measuring it via an audacity recording may not give it a fair representation, since the audio input to most computers is designed for a high-impedance microphone, and may not present the expected load impedance.? Having said that, I will also say that I have measured my QMX audio via audacity recording, after carefully setting the levels (QMX volume setting and computer input setting), and it does not look distorted like what you show, so there may indeed be some fault with that particular QMX+, or with the recording setup details.
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But the bottom line is that my experience with both my QMX and QMX+ is that they produce excellent audio, and that your message title of "severe QMX+ audio distortion" is certainly not what you can expect from this design.
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Stan KC7XE
 

I agree with Stan on this. All of my QCXs and QMXs have great audio. It's possible to make them distort with maladjusted AGC, but if you set it right, or turn it off, the audio is great. The QCXs benefit from a 1K ohm resistor on the wiper to make them a bit more linear, but the QMXs digital volume works great.?
--
73, Dan - W2DLC
 

On Sun, Dec 22, 2024 at 04:35 PM, Chuck @ w8mqw wrote:
I've been annoyed by the audio quality of some earlier kits
Chuck, I would seek some common denominator in your rig. These kits sound great. Sounds to me like you have an inpendance mismatch in your external audio monitoring.?
Ted
2E0THH?
 

It seems to me that "severe" and "awful" are extreme adjectives that deserve comparison.? "Awful" compared to what?? For example, Thomas Witherspoon often praises the audio quality of the Penntek TR-45 Lite. In comparison, I find my QMX (same audio circuits as QMX+) to sound better than my TR-45, and less tiring to operate.? To what field-portable QRP rig are you comparing the QMX+ ?? (Anans and Flexes are probably not fair comparisons.)
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72 de N4REE, Bob Easton - QRP CW forever
 

The Agency (TV Series 2024–)

On Mon, 23 Dec 2024, 15:38 Ted 2E0THH via , <qrp=[email protected]> wrote:
On Sun, Dec 22, 2024 at 04:35 PM, Chuck @ w8mqw wrote:
I've been annoyed by the audio quality of some earlier kits
Chuck, I would seek some common denominator in your rig. These kits sound great. Sounds to me like you have an inpendance mismatch in your external audio monitoring.?
Ted
2E0THH?
 

On Mon, Dec 23, 2024 at 03:37 AM, N4REE - Bob wrote:
It seems to me that "severe" and "awful" are extreme adjectives that deserve comparison.? "Awful" compared to what?? For example, Thomas Witherspoon often praises the audio quality of the Penntek TR-45 Lite. In comparison, I find my QMX (same audio circuits as QMX+) to sound better than my TR-45, and less tiring to operate.? To what field-portable QRP rig are you comparing the QMX+ ?? (Anans and Flexes are probably not fair comparisons.)
--
72 de N4REE, Bob Easton - QRP CW forever
I didn't realise the QMX+ would demodulate ssb, I thought with the great narrow filters it was optimised for cw.?
I must give it a try when I get back to my rig.
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Paul
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--
G0TXL (Paul)
 

When you do, remember to set the mode to digital, not cw.

73
Roger
8P6RX

Get
On 23 Dec 2024, at 11:43, "G0TXL via " <pelliott.co.uk@groups.io target=_blank>[email protected]> wrote:

On Mon, Dec 23, 2024 at 03:37 AM, N4REE - Bob wrote:
It seems to me that "severe" and "awful" are extreme adjectives that deserve comparison.? "Awful" compared to what?? For example, Thomas Witherspoon often praises the audio quality of the Penntek TR-45 Lite. In comparison, I find my QMX (same audio circuits as QMX+) to sound better than my TR-45, and less tiring to operate.? To what field-portable QRP rig are you comparing the QMX+ ?? (Anans and Flexes are probably not fair comparisons.)
--
72 de N4REE, Bob Easton - QRP CW forever
I didn't realise the QMX+ would demodulate ssb, I thought with the great narrow filters it was optimised for cw.?
I must give it a try when I get back to my rig.
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Paul
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--
G0TXL (Paul)
 

With the latest firmware you can just set the CW filters to NONE.
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73, Dan - W2DLC
 

QMX distorted compared to what?? What do you call good?
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Besides QCX, QDX, QMX? I have a large assortment of radios
commercial, some kits(3), some of my design(5).
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Among the commercial:
Tentec Argonaut 505,?
Tentec Triton? M340
Tentec 6n2? ? M526
Tentec Eagle M599
icom IC7000
Icom IC7300
Yaesu FT817
Yaesu FT736R
Kenwood TS44S/AT (2 of them)
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The QMX I have sounds as good as any of them and better than
the kenwoods (sorry).
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Also the CW audio sample sounded saturated like excessive gain/volume
was being used.? The other was the SSB example had significant
multipath distortion unrelated to the radio.? That and with SSB?
not every operator puts out good audio quality.
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--
Allison
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