ELEC 241 Lab

The Receiver

The receiver consists of three parts. The first is the amplifier and filter on the Antenna Interface, the second is a Labview program to demodulate the received signal, and the third is the earphone amplifier. Two of these are already built, which leaves the Labview program. From our work in the Design section of this Lab, it appears that the receiver is only slightly more complex that the transmitter. In fact, we could use the transmitter VI as a receiver, but it would sound pretty bad without the filters.

The Receiver VI

If you would like to practice your Labview programming skills, you can make a copy of the transmitter VI and modify it as follows:

  1. Remove the adder (which computes $m(t)+1)$ between the A/D output and the multiplier input
  2. Replace it with a bandpass filter: bring up the Functions palette, select Analysis, then click on Filter. In the Configure Filter dialog, select Bandpass for the filter type and choose appropriate values for the other parameters.
  3. Similarly, insert a lowpass filter between the multiplier output and the D/A input.
  4. Change the A/D input channel to ach4 and the D/A output channel to ao1.
If you're fed up with Labview programming, or don't have the time to get a receiver VI working, a prefabricated receiver VI (with some additional bells and whistles) is available. You can load it from the Start menu by following the path Programs ->ELEC 241 ->Radio Receiver.

The Earphone Driver.

We can reuse the earphone the earphone driver amplifier from Experiment 6.2:

\includegraphics[scale=0.650000]{headphone_amp.ps}
If yours is the worse for wear (or has been disassembled) rebuild it now.

Connections.

Connect the receiver output of the antenna interface to the input of the Receiver VI (ach4 on pin 46 of the interface connector). Connect the demodulated output of the Receiver VI (dac1 on pin 52) to the input of the earphone driver.

Testing.

Set the function generator to produce a 2 mV 174 kHz sine wave. (To get such a small amplitude, pull out the amplitude knob and rotate all the way counter clockwise.) Connect the function generator output to the J4-1 on the Antenna Interface module.

Start the Receiver VI. You should observe a 1 kHz output from the receiver.