9
Radio transmitter circuits for simulation in LTspice.
Radios, transmitting.
This section contains several radio ccts in transmit mode.
Firstly download and install LTspice from www.analog.com
Then click on the names below to open the circuits
In case of difficulty downloading here are the circuits as a ZIP file
![the circuits in this section as a zip file]()
CW, this is TBD
Amplitude modulation (AM).
This section has three different methods of producing AM, the most efficient of these is superimposing the audio signal onto the supply rail, the other methods are inefficient as they use linear power amps.
AM by superimposing the audio signal onto the supply rail.
This is the most efficient way of producing AM, as you can use a class C, or class D power amp with AM applied to the voltage supply rail.
![AM_by_applying audio to Vcc using linear.asc]()
![AM_by_applying audio to Vcc using SMPS.asc]()
AM by modulating the gain of a class A power amp.
This is possible but inefficient, as the following power amp has to be linear.
this is the same variable gain ampilifier as is suggested for AGC in the amplifiers section, but with longer simulation and different instructions.
AM by unbalancing a diode mixer.
This is possible but inefficient, as the following power amp has to be linear.
Frequency modulation (FM).
The example circuit here uses a Colpits oscillator, frequency modulated with a varactor diode, followed by a class D power amp.
The class D power amp could be replaced by a class C power Amp, it is unlikely that you would use a class A, class B, or class AB power amp though, as these would be less efficient meaning bigger heatsinks and bigger power devices.
![FM class D]()
Single sideband (SSB).
The 4Mhz simulations work as intended selecting just one sideband.
The 38.4Mhz circuits, have too wide a filter passband at 16khz, and hence cannot generate SSB.
After a few circuits you may be able to ignore the directions written on the cct diagrams, as LTspice is reasonably simple to operate.