Total posts : 45366
The intention of my test was to discover what the subjective effect to audio is due to a single pole, or at least a single dominant pole. This is only a first step to determine if a single pole at a low frequency so distorts the audio that further tests are not necessary, or if the results are good enough to warrant further effort. I found that a single pole at a low frequency leaves the audio acceptable.
I think it is possible that a single pole at a sufficiently low frequency will dominate the other poles of the passband response, and the multiple poles of the shap cutoff IF skirts. In one variation of my test setup, I used an AM receiver with poor bandwidth to supply the audio input to my test fixture, which comprises an RC low-pass filter and a buffer amplifier. The addition of the low-frequency pole to the frequency response of the AM receiver still left the audio acceptable.
Certainly, if an AM system with a very high Q antenna is constructed, the complete system should be tested. The source of at least two more poles to the complete system is the tuning circuit that couples the transmitter to the antenna. This tuning circuit is often neglected in determining the efficiency of a Part 15 AM system. In a previous post by me in this thread, I explain how the tuning circuit affects system efficiency.