Crystal Set's

Only one project here at the moment it has a virtual AM transmitter transmitting a virtual 1000 Hz sine wave to a virtual crystal set.

To run this simulation to do so you will need LTSpice loaded on your PC. Thanks to Linear Technology this is a free download.

http://www.linear.com/designtools/software/

A simple AM transmitter was drawn up using a conventional Colpitts oscillator circuit.

A simple "crystal set" was drawn up using the output from our simple transmitter.

Looking at the transmitter.

Below is a view of test_point_A showing the 1000 Hz signal as fed into the transmitter modulation transformer.

Below is a view of the RF (Radio Frequency) output of the transmitter showing the 1000 Hz amplitude modulated carrier.

Now looking at the "Crystal set"

Below is a view of the RF at Test_Point_c, notice the top of the modulation envelope is crushed slightly, this is due to the detector diode D1 turning on and removing power from the tuned circuit.

Below is a view of the demodulated audio signal at at Test_Point_D, notice the bluring of the waveform, this is due to some of the carrier RF remaining on the audio signal. C8 is used to remove the RF component, in practice this is normally not fitted because the headphones will not respond to the high frequency carrier i.e. the frequency response of the headphones is already a low pass filter.