Re: New assembled High Bands QDX went into smoke
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When the modulated supply voltage goes to zero, we expect the output to go to zero. It does not. No surprise. Apparently signal is feeding through the BS170 gate-drain capacitance to the LPF and output. It is not much, but it is suggesting that attaining deep carrier suppression could be difficult in this SSB generation scheme, without some TBD magic.
I also can see deviation between my audio sine wave and the envelope of the modulated output. Again, not much, but there is some distortion. It needs further exploration.
This suggests to me that we should not expect the level of SSB performance we get in $1K-$3K transceivers out of this scheme,? but it by no means precludes an acceptable and useful radio.
I agree, and were this not the case, everyone would be using EER for ham radio transceivers.?
Practically speaking I measured a 37dB control range over the RF amplitude, without magic; and a high level of control linearity. Perhaps some magic may be found to achieve a few more dB on top of that.?
During development, my comparison here was to the uSDX scheme, which applies a PWM-derived gate bias to the Class-E BS170s triplet. uSDX uses a 10-bit PWM control but due to the design, only the least significant 8-bits are actually usable; however according to my own measurements, only about 20dB of actual amplitude control range is realized in practice; furthermore as you might easily have expected, the control voltage to output voltage has a characteristic S-shape rather than a linear straight line.
uSDX has quite a collection of fans; I am in no doubt that the SSB performance is intelligible though probably not stellar. Regarding QMX it is my belief that with 37dB of amplitude control instead of 20dB, and with the very much greater CPU performance available by the use of our 168MHz 32-bit ARM Cortex-M4 with its floating point unit and DSP instructions, it ought to be reasonably expected that EER would produce a noticeably improved SSB performance compared to uSDX.?
HOW good, remains to be seen, the proof of the pudding being as always, in the eating.?
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