In my wanderings around the web I've just come across the TalkingElectronics site. In its vast compendium I latched on to the 27MHz section with descriptions of the circuits used in toy remote controls. I was intrigued by the connection of the receiver antenna to the collector of the Common Base RF amplifier. (See the first receiver circuit at http://www.talkingelectronics.com/projects/27MHz Transmitters/27MHzLinks-1.html)
There is lots of explanation and multiple variations shown, but unfortunately I seem to be on a different wavelength to the author and could not understand the circuit.
It looks like a CB amp, but with 100% positive feedback (the 39pF cap) making it an oscillator (Colpitts?) Even as an amplifier, it is strange to feed the signal into the collector, (though one can see why they might want to do this: later on they show ccts where the same stage is used as both receive amp and transmit output in a walkie-talkie.)
So I'm wondering if anyone here can shed some light on this cct, in particular the role of the 39pF capacitor from C to E and how its value is determined?
There is lots of explanation and multiple variations shown, but unfortunately I seem to be on a different wavelength to the author and could not understand the circuit.
It looks like a CB amp, but with 100% positive feedback (the 39pF cap) making it an oscillator (Colpitts?) Even as an amplifier, it is strange to feed the signal into the collector, (though one can see why they might want to do this: later on they show ccts where the same stage is used as both receive amp and transmit output in a walkie-talkie.)
So I'm wondering if anyone here can shed some light on this cct, in particular the role of the 39pF capacitor from C to E and how its value is determined?