Total posts : 45366
I understood your description of the test you did with an audio source and filter and my last post here was intended to provide another explanation of a perceived problem which I once attributed to antenna Q which may not be the true cause of the observed effects.
My models and observations indicated a distortion of both the RF waveform and the modulated envelope as I described. The observed distortion of the expected sine wave of the unmodulated RF carrier was not due to antenna Q since it was not sinusoidal. Pending further tests it appears that the SSTRAN, when presented with the load of my antenna system, produces distortion most likely due to a load with which the circuit cannot function properly. This does not appear to be an issue involving antenna Q.
Using the generally accepted values for antenna capacitance (30 pf.), resonant loading coil inductance (300 uH.) and antenna system resistance (20 ohms including ground) I calculate a Q of 150. This yields a bandwidth of 10 kHz. at 1670 kHz. Unless I have an atypical antenna and ground system in terms of low resistance, it is not probable that high Q caused the effect I reported.
Your report of the effect of single pole low pass filtering on an audio signal is duly noted and appreciated. My report indicates that with this particular transmitter and with my antenna system that bandwidth is not the cause of the problem that I observed. The excellent performance I have has resulted by installing the 820 ohm resistor in the circuit. PhilB has posted that this is approximately the load which the circuit is designed to drive and it leads me to conclude that my antenna system is nowhere near presenting an appropriate load to the transmitter rather than being a problem with antenna Q.
I would appreciate your comments since I might be overlooking something.