There are two sine wave oscillators in the Elecraft 2T-gen. The first one is at 700 Hz, and the second one at 1900 Hz. I tested both oscillators with an analog oscilloscope. The 1900 Hz tone appeared perfect on the screen, but the 700 Hz tone showed distortion (clipping), and this is not acceptable in a test generator. Obviously, the problem was too high amplification in the circuit, and this pointed to poor AGC control.
I tried to solve the problem and eliminate the distortion. After some time, I gave up the MOSFET-based AGC and decided to implement a different method: Using a light bulb as automatic gain control. Here is the final circuit diagram:
|Two-tone generator: circuit diagram.|
|The generator is mounted inside an alu-box.|
|Front plate of generator.|
A small 12V 40 mA light bulb worked just fine as AGC. The settling time (stable amplitude) is about 2 seconds. If you are looking for a similar light bulb on ebay.com, I recommend searching for "12V 40mA".
OZ1BXM Lars Petersen