Amateur Radio Association of Lanka

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Prepared by Achira - 4S6DDA

This experiment was done when I was a SWL & also studying for RAE in year 2000. This circuit was based on a FM radio originally made for receiving FM broadcast stations. I modified its RF coil & local OSC coil & removed BPF at the front end & replaced a 50 ohms matching part to suitable 50 ohms antennas. Also AM section was disabled in the receiver.

As this design is a single conversation receiver & trying to receive narrow band FM signals, it might be difficult to lock the tuning between 144 MHz & 146MHz. But once locked it receives 2M signals nicely.

A homebrewed ground plane antenna was used during the experiment to receive a local repeater on 145.625 MHz. Later connected a homebrewed 8 element beam with a folded dipole antenna. Both worked with this receiver without any problems.
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This IC is all-in-one chip made to receive FM broadcast stations. This Integrated chip has a FM front end RF AMP, Local OSC , 10.7 MHz IF section, FM quadrature detector & an AF power amplifier. Additionally it has tuning meter, FM AFC & Also a variable capacitance diode for fine tunings arrangement.
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After I got the radio amateur license, this modified radio was gifted to a friend of mine who is an another SWL & therefore I don't have it now to publish photos with this article. Also I didn't prepare a PCB pattern, I only modified a working FM radio.

My next experiment with KA22426.
First a PCB pattern will be designed. As this chip has a variable capacitance diode , an AFC block. So a manual variable capacitance diode tuning system will be added using the internal very cap diode. Also will add a tunings meter system to indicate signal strength an S meter level. All modifications will be published here when the experiment will be completed.