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QMX+: low RX sensitifity @ 6m / 22 dB noise floor / 1500 Hz wistle

 

Hello,
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I? recently build QMX+ and noticed a huge
noise floor and wistling a 6 m.
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Therfore I measured sensitifity using a signal generator.
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Band [MHz] Sens [dBm]@Noise+10dB Noise [dB]
1,85 -100,0 0
3,65 -106,0 0
5,35 -107,0 6
7,07 -107,0 0
10,14 -110,0 2
14,23 -107,0 1
18,1 -103,0 4
21,04 -99,0 9
24,9 -97,0 7
28,1 -103,0 5
50,5 -79,0 20
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Method: injection of signal Rx frequency + 1,1 kHz Mode: Digi
Noise: signal detected by WSJT-X
Sens: Noise floor + 10 dB
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Noise floor is increasing by frequency, but at 6 m wistling and digital noise make RX unusable.
Output at 6m is about 2 W at 9V Vbat (12V Version)
1,5 kHz wistle starts at 20 m and is increasing by frequency
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Using wsjt-X i evalating waterfall diagram: (QMX+ at 50 Ohm)
AVE:1, cumulative
Noise [dB] : signal by WSJT-X
?signal in waterfall diagram AU?
QMX+ ? ? freq [Hz] freq [Hz] freq [Hz] freq [Hz] freq [Hz] freq [Hz]
Frequency [MHz] Noise [db] Noisefloor 500 1000 1500 2000 2500 3000
1,84 0 0,2 0,2 0,2 0,8 0,2 0,2 0,2
3,57 0 0,3 0,3 0,3 0,7 0,3 0,3 0,3
5,3 1 0,5 0,5 0,5 1 0,5 0,5 0,5
7,04 5 0,8 0,8 0,8 1,1 0,8 0,8 0,8
10,1 1 0,5 0,5 0,5 0,5 0,5 0,5 0,5
14,1 1 0,5 0,5 1,3 2,8 2,1 0,5 1,5
18,1 5 0,8 1 1,8 2,3 2,1 1,1 2
21,1 7 1 1 2,1 2,6 2,1 1,1 2,1
24,9 7 1 1,2 2,7 2,8 2,7 1,3 2,5
28,1 7 1 1,2 2 1,5 1,5 1,2 2,2
50,3 22 1,8 2,5 3,8 4,2 3,9 2,8 3,8
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At higher bands 1,5kHz signal is constant and independent from RX freuqency.
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At 6m additional audio signals are appearing.?
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6m RF Filter seems to be ok.
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Any suggestions to detect cause?
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vy 73 Michael (DF6TV)
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Hi Michael, there is already a thread covering this ¡­..

QMX+ with ~1000 tone on 12M & 6M

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I did sent it to Hans direct some time ago but so far no response. I also see the poor sensitivity on 6m.
No-one on the forum seems to have come back with a solution yet.
73 Ken G4APB
 

Are you hearing the whistle on all modes? I only hear it on the upper bands when in LSB.
 

Since factory resetting a couple of times and installing the latest SSB firmware, the noise has mostly disappeared from my QMX+. My QMX HB never had the problem. It appears to be solvable.
--
73, Dan - W2DLC
 

On Thu, May 8, 2025 at 04:50 PM, Daniel Conklin wrote:
Since factory resetting a couple of times and installing the latest SSB firmware, the noise has mostly disappeared from my QMX+. My QMX HB never had the problem. It appears to be solvable.
--
73, Dan - W2DLC
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?Thanks Dan but I am reluctant to install the latest SSB firmware as it seems to be bring in other as yet unsolved problems (PAs failing during calibration). I also am not happy with problems that just ¡®go away¡¯ without explanation. The SSB firmware is not listed as tackling this issue. I will just be patient until someone finds the cause (and a cure hopefully).?
73 Ken G4apb?
 

Hi Ken

Using SSB without calibration is perfectly acceptable, the audio is still good. Calibration just makes it even better.

73 Hans G0UPL


On Thu, May 8, 2025, 19:54 KEN G4APB via <lfoofui.nbz42=[email protected]> wrote:
On Thu, May 8, 2025 at 04:50 PM, Daniel Conklin wrote:
Since factory resetting a couple of times and installing the latest SSB firmware, the noise has mostly disappeared from my QMX+. My QMX HB never had the problem. It appears to be solvable.
--
73, Dan - W2DLC
?
?Thanks Dan but I am reluctant to install the latest SSB firmware as it seems to be bring in other as yet unsolved problems (PAs failing during calibration). I also am not happy with problems that just ¡®go away¡¯ without explanation. The SSB firmware is not listed as tackling this issue. I will just be patient until someone finds the cause (and a cure hopefully).?
73 Ken G4apb?

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