500 mW VHF Video Transmitter

Description

Q1 (BC548C) is a modulated oscillator operating in the Commercial VHF Television Band and Q2  (BC548C or 2N4427) is an VHF RF Amplifier.

Tuned circuits consist of C4, L1, C8, L3, and the two 15 pF trimmer capacitors across the collectors and emitters of both transistors. Other NPN transistors like BC54, 2N3642, 43, etc should also work.

The circuit is designed for simplicity, so "No Audio" has been included as this would involve adding at least an RF coupling transformer. The main use for this circuit is for "Security Monitoring".

L1 and L3 can be molded chokes, however, you could use 3-4 turns of insulated copper wire about ¼” diameter. Just spread them until you see a signal.

[VR] is the video balance. It’s adjustment will depend on the type of video input you provide.

If you use a 2N4427 or similar transistor for Q2 (output), you must use a heat sink. The 2N4427 is capable of delivering 1 Watt of RF at VHF frequencies so be sure that either a 50-75 Ohm dummy load or antenna is connected at all times before applying power.
 
Any composite output device will work. Cameras, game consoles, etc.  Tune the transmitter to an unused channel.

Note: You should use an old Analog Tune TV with an indoor antenna.

Designer & Author: Special thanks to Laszlo Kirschner.