100 MHz modulated RF source : can be used to tune up those 100 MHz TRF stages. 

4 MHz amplitude modulated RF source : the only tuned component is the crystal 

AM / FM / SW Active Antenna: This circuit shows an active antenna that can be used for AM, FM, and shortw1ave SW. On the shortw1ave band this active antenna is comparable to a20 to30 foot wire antenna. This circuit uses receivers that use untuned wire antennas, such as inexpensive units and car radios. L1 can be selected for the application 

AM Loop Antennas By Bruce Carter:

AM Receiver:

AM Transmitter:

General Purpose RF Amplifier:

Limiting Amplifier Forms AM Modulator: EDN-Design Ideas 

Micro Power AM Broadcast Transmitters: In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a Class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable VFO with a capacitor/resistor combination. 

Pi Section Coupler:

:

Simple AM Radio Receiver & Amplifier:

TRF AM Receiver Circuit:

Unamplified Four Foot Box Loop: