It was measured at about 3db above the noise floor. When the above signal was not present, and looking closer (at the same high gain setting) an even lower level signal was always present. It was measured about 15db above the noise floor on the Analyzer. It appeared only about 50% of the time, and after an RF output. On occasion, a very Low Level signal appeared on the Analyzer between RF transmissions, and near (slightly lower) the intended test 10.140MHz signal that I was using for the experiment. The Filters passed with with flying colors. Again, with the loan of Jeff's Spectrum Analyzer the task was made easy. The Filters are intended to be connected directly to the Propeller board via a cable and SMA connectors. The last few days I have been building and attempting to characterizing a new set of Low Pass Filters (see previous post). I was a little bummebed out, as it meant that I needed to rework my faulty (guilty) PA design to provide some neutralization. According to the Analyzer, the Oscillation was NOT on the Frequency of my Beacon (10.140MHz), but at slightly lower unknown frequency. Oscillation (Gremlins) can easily occur on untried designs. I (some what) expected this to happen, as the PA was built to be a wide band amplifier with only some filtering on the output. The oscillation only happened once in a while. Harmonics were well below requirements and that was very good news.īut, during the inspection we noticed that once in a while the PA appeared to jump into low level oscillation, and some how it was associated with the make-shift connection to the Propeller board. Jeff - KO7M brought over his Spectrum Analyzer so we could look at the output. I was a little reluctant to put it on the air, as I did not know the output characteristic and the effectiveness of the included Low Pass Filter. Several weeks ago, I built a Power Amplifier (PA) for my Propeller 30m Beacon (at 10.140MHz).
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