ph2t
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RX analysis
What we have is an AM Super-regen receiver on the car that is tuned to receive a serial encoded OOK AM transmission (whatever that is).
The centre frequency is tuned (27Mhz, 35Mhz, 40Mhz, 45Mhz, 49Mhz, and 57Mhz) so the receiver is most “selective” on one of these frequencies. More information can be found here and here.From what i’ve read up about regen receiver designs is that they are super-sensitive, BUT not very selective. That’s why we have the requirement of such a wide seperation between controller frequencies (approx 8MHz).
I’ve isolated the receiver circuit to help understand the roles of the various components.
1) The Base Oscillator
This part of the circuit provides positive feed back to the transistor and gives the AM receiver a high gain, or in other terms high sensitivity to an incomming signal.
The Tuned LC Circuit
The capacitor and inductor run at the RF frequency you want to receive the signal on, eg: 27Mhz, 35Mhz, 40Mhz, etc…
The value of the inductor can be tweaked to acheive the strongest signal for your car. This also gives you better distance.
The tuned circuit is the throttle for the base oscillator. Through the transistor it amplifies the signal it receives from the controller.
The Q Capacitor
This part of the receiver is the one I think we want to look at.
This capacitor controls the Quality of the transistor amplifier. Quality (or Q) is a hard thing to describe. It’s like looking at a fountain of water side on and noticing the upsidedown U. Quality is the width of this upsidedown U. Higher quality, thinner U. Lower quality, fatter U. Confused?
With this we might be able to make the receivers on the cars more “selective” and then mod them with inbetween freq’s such as 31Mhz, 37Mhz, etc…
ph2t.
