FM ICs in AM receiver

[raiya_23]

I have a ciruit diagram of an AM RECEIVER (118Mhz-136Mhz) in which the IC CA3075(FM IF AMPLIFIER LIMITER) and CA3012(FM IF WIDEBAND AMPLIFIER) are being used. I dont get it why are FM ICs being used in an AM receiver.Please help.

 

[keith1200rs]

I think you need to show the source of the information. If you put AM through a limiting amplifier there won't be much amplitude information left!

Keith

 

[FvM]

Without referring to the specific usage of the chips in the AM receiver, the question is about meaningless. CA3075 might be e.g. used for an AFC circuit,

 

[jiripolivka]

The CA3012 is a linear amplifier, so it can be used for any modulation. Limiting amplifiers like CA3075 are only suitable for other than AM. By the way, the frequency band 118-136 MHz is mostly used for NBFM (narrow-band FM) signals, so your receiver may not be an "AM" type.

 

[keith1200rs]

The CA3012 data sheet I have says it is a limiting amplifier. It may be linear below the limiting voltage (around 300uV).

Keith

 

[vfone]

I agree. CA3012 cannot be used for AM demodulation at all. The only internal stage that can be used in a AM receiver is the audio preamplifier, which is available at pin 14 and pin 12.

 

[FvM]

By the way, the frequency band 118-136 MHz is mostly used for NBFM (narrow-band FM) signals, so your receiver may not be an "AM" type.

118-136 MHz is air band (aviation communication). It's using AM, except for WX (weather information) sent as FM.

A dedicated airband transceiver or receiver will most likely have both AM and FM capability.