Hello Ken,
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I am also skeptical about my cure and therefore I made several measurements to find sources of noise and constant tones of my QMX+.
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In post #144992 I show the Lo signal @6m with strong sidebands (lines) around strong LO signal.
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The LO signal was detetected connecting the BNC of QMX+ to a spectrum analyser (LibreVNA operating in spectrum-analyser mode, QMX+ in RX, DIGI mode)
LO signal is 12 kHz below RX frequency.
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Another OM with same QMX problems verfied my obseraton (sidebands around LO signal) using a SDR RX and waterfall diagram.
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After resoldering trifilar and handling PCB strong sidebands are gone but 1500 Hz tone remains, and I am happy QMX is working, but I am unhappy that I find no cause (QMX is working at lower bands).
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In meantime I tried o understand detection technique of QMX (Tayloe detector)and to find a method to quantify signal strength of tones and make it reproduceable using wsjtx.
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Measurements are on-going and I will post my results in next time.
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@all: Can anyone with RX problems (high noise and addtional tones at higher bands) verify my observations of sidebands around LO signal?
???????????????? - Switch QMX in RX only mode, connect BNC to another RIG and observe spectrum 50 kHz around
???????????????? RX frequency (e.g. SDR and waterfall diagram).
??????????????? - Signal strength is between -40dBm - -130 dBm.
??????????????? - Please report additional signal strength in wsjtx (dB indicator at main page of program)
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Vy 73 Michael
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