AM demodulation is a nonlinear process and AM BW
testing using noise input is meaningless.
The filter bandwidth cannot be reliably estimated
from the resulting audio spectrum measurements
because of the unknown spectral components generated
by the nonlinear demodulation process.
The testing can be done reliably in two ways:
a) using a carrier swept around to determine bandpass edges, or
b) using an amplitude modulated signal with the carrier centered
in the bandpass, and modulation frequency swept to determine
edges.
Just to be sure, I've retested V1.373b5 and V2.056,
using both of the above methods (BW set at 6 kHz):
a) V1.373b5 bandwidth is 12 kHz (center +/- 6 kHz)
V2.056 bandwidth is 6 kHz (center +/- 3 kHz)
b) V1.373b5 is capable of reproducing up to 6 kHz modulation
V2.056 is capable of reproducing up to 3 kHz modulation
Therefore, the entire audio spectrum of AM broadcasts
can not be received using V2.056 (and probably Orion II).
Furthermore, attempting to amplitude-demodulate only the carrier
and a single sideband generates nonlinear distortion, caused by
the fact that the resulting RF envelope no longer represents
the audio signal faithfully.
A single sideband of an AM signal can be demodulated without
distortion by a linear process, i.e. a product detector supplied
with a carrier of the proper frequency and phase. But this is not
possible with Orion.
73,
Sinisa YT1NT, VE3EA
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