Re: QMX S9+ noise on receive
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Bruce,
The PCM1804 is likely bad.
That chip has been exhibiting a very wide range of failure symptoms in QMX, from subtle and noise related to complete meltdown. Yours appears to be a case of damage to the I channel but not so bad as to leave the device completely dead.
If you are not confident about your ability to change it, consider help from Jeff Moore W1NC, repair wizard and all-around good fellow.
JZ KJ4A?
So I am making a second post. I recently assembled a QMX. Fired up at 7v limited to 200ma. Loaded the firmware. The transmit on all band is great with 4 to 5w. This is a 60 to 15m model.
The problem I have is it is mostly deaf. Only if a station is like S9+20 will it exceed the noise level and be able to be heard.
I am posting various sweeps here. First the swr sweep for 40m looks good to me.
Then the RF 40m sweep looks good to me also.
Then the 40m lpf sweep, again I see no issues.
Now the image sweep. This compares favorably to the manual so I believe this is good as well.
Now the AF image sweep. This is similar to the manual, but my lsb is only down -40 and not -60 like the manual shows. I am not sure what would cause this.
Lastly the ADC sweep that Hans just created. I see the I and Q 90 degrees out of phase so I believe that proves my tri filar torroid is fine. The sweep however is not clean like the example. There is significant noise, at least it appears that way to me.
Please if anyone can help. I have my suspicions it is the PCM1804, but I am not an engineer.
Thanks everyone.
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