CB FM mode TX/RX add-on PCB kit for 455kHz IF in AM & some multimode rigs. | eBay
As such it would make a mid block USA AM rig compatible with the EU FM block. This board connects to the detector end of the IF chain in the receiver to demodulate any FM signals at 455kHz. It also applies clipped audio to the varicap in the synthesizer to generate FM on transmit.
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This is an FM conversion board. They have 4 left at the moment.