Re: HA12411 FM IF chip - who used it?
remember that as FM signals are frequency modulated and a multipath path difference can be many wavelengths, the created nulls will be sharp enough that the frequency variation due to modulation will move the resultant signal up and down the slopes of nulls, creating AM on the signal, possibly (modulation) frequency doubled AM.
If the reflected signal is weak, the nulls/peaks are less developed and the amount of AM is less.
Less than perfect flatness in the transmitter or mistuning of the receiver RF stages can also create some AM without there being multipath conditions.
The reflected signal path length will change if its from a moving object, giving varying AM effect... Aircraft flutter.
Oh and all this AM can get back into the received audio via AM to PM conversion in an mperfect limiter in the IF.
Once you dig into it, there's quite a mess!
David
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