Rev0VTx Modulator
This page describes the 5.5 MHz Audio Subcarrier AM Modulator for the rev0VTx video transmitter.
Summary
The modulator is based on the topology used in the HobbyKing 900 MHz Video System. The design uses two BC817 (or similar) NPN BJTs, with a series resonant circuit made of a 10uH SMT inductor and variable/fixed capacitor. The first transistor forms the oscillator, and is amplitude modulated by applying the ~1-2Vp-p audio signal to the collector. A second transistor amplifies the modulated carrier. The board runs from a single 5V supply. The design was simulated and evolved in LTSpiceIV, using the built-in BC817 model. The Spice circuit for simulation can be found here: http://www.rev0proto.com/files/rev0VTx_MOD_Sim.asc The gerbers, Eagle schematic and board file can be found here: http://www.rev0proto.com/files/rev0VTx_MOD.zip
Testing
PCB/Construction Photos
- Rev0VTx MOD PCB Bottom.jpg
Bottom of unpopulated PCB
- Rev0VTx MOD PCB Top.jpg
Top of unpopulated PCB
- Rev0VTx MOD Top.jpg
Populated PCB