Cobra 142GTL

COMPONENTS

Schematic Diagram

MB8719 PLL Frequency Synthesizer

S042P Duble Balanced Mixer

AN612 Balanced Modulator (SSB Modulator)

TA7222AP Audio Power Amplifier

2SC1969 RF Finale Transistor

2SC1306 RF Driver Transistor

2SC1973 RF Buffer Transistor

Quieting of AM reception and improving gain of incoming signals is a common request from radio operators. In the first stages of the HF input 2SC1674 transistor can be found. This transistor is responsible for the amplification of a small detected signals. A problems exist if the transistor itself is noisy as is such the case of the 2SC1674 when compared to other low noise packages. Along with the amplification of the incoming signals is transistor noise. Replacement of this transistor with a higher gain, lower noise transistor greatly improves the signal to noise ratio of your receiver.
We will use an 2SC2999 transistor that has higher gain lower noise characteristic. Replace the 2SC1674 (TR9) with an 2SC2999 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio.
Re-Adjust L3 and L4
The gain will improved with more than 6dB with the same signal to noise ratio.