neazoi
Advanced Member level 6
Hi I have designed this transceiver which is capable of upper sideband (USB) detection whereas keeping the LSB in AM mode and attenuated. So sort of single signal reception.
This works like a charm, however I do not know the internal mechanism of why this is happening and this is what I want to investigate.
I have drawn a small diagram of how it behaves. The RX Losc is the frequency of the crystal. The USB and LSB are two hypothetical signals received at both sidebands. The curved line is the "detector effectiveness". Below and at the right side of this curve, the detector is effective and can detect USB signals. Above and at the left of this curve, the detector detects only attenuated AM signals.
The diagram shows the case where the receiver regeneration is set at the threshold point of oscillation (just oscillates). In this case, USB signals are received ok but LSB signals are heard like receiving an SSB signal on an AM radio, and also they are much attenuated. This is the single signal (USB) reception case.
From that state, if you increase further the regeneration, the curve moves at the left and the low audio frequencies of the LSB signal, start to be detected effectively as well as the USB signal. IF you increase regeneration even more, all audio frequencies of both sideband signals are detected (DSB detection).
In single signal mode, (like the diagram shows) if however you decrease the regeneration, the curve moves to the right and the low audio frequencies of the USB are cut-off (not detected effectively). If you continue to decrease the regeneration the USB signals are cut-off completely.
So with this I explain what happens. But I do not know WHY it happens, what are the internal mechanisms that allow such behaviour to happen and why it only happens on crystals and ceramic resonators and not on LC resonators?
This works like a charm, however I do not know the internal mechanism of why this is happening and this is what I want to investigate.
I have drawn a small diagram of how it behaves. The RX Losc is the frequency of the crystal. The USB and LSB are two hypothetical signals received at both sidebands. The curved line is the "detector effectiveness". Below and at the right side of this curve, the detector is effective and can detect USB signals. Above and at the left of this curve, the detector detects only attenuated AM signals.
The diagram shows the case where the receiver regeneration is set at the threshold point of oscillation (just oscillates). In this case, USB signals are received ok but LSB signals are heard like receiving an SSB signal on an AM radio, and also they are much attenuated. This is the single signal (USB) reception case.
From that state, if you increase further the regeneration, the curve moves at the left and the low audio frequencies of the LSB signal, start to be detected effectively as well as the USB signal. IF you increase regeneration even more, all audio frequencies of both sideband signals are detected (DSB detection).
In single signal mode, (like the diagram shows) if however you decrease the regeneration, the curve moves to the right and the low audio frequencies of the USB are cut-off (not detected effectively). If you continue to decrease the regeneration the USB signals are cut-off completely.
So with this I explain what happens. But I do not know WHY it happens, what are the internal mechanisms that allow such behaviour to happen and why it only happens on crystals and ceramic resonators and not on LC resonators?
