Sommerkamp TS-789DX FM/AM/SSB CB-Radio

Block Diagram

Adjustment

Test equipment required:


Power Supply: 13,8 V	Frequency Counter	Dummy Load 50 ohm	Oscilloscope
RF Power Meter	DC Amperemeter	RF SSG	AF SSG

Preparation alignment:


Fine	Mid.
Clarifier	Mid.
SQ GAIN	Max.
AF GAIN	Max.
RF GAIN	Max.
MIC GAIN	Max.
NB/ANL	Off
MID Band, Ch. 19	Frequency: 27.185MHz

Reading Point	Condition	Adjustment	Procedure
PLL
IC8 #4	RX AM	L21	10.2400MHz
IC8 #4	RX USB	L22	10.2425MHz
IC8 #4	RX LSB	L23	10.2375MHz
D32	TX AM	L27	10.6950MHz
D32	TX USB	L28	10.6975MHz
D32	TX LSB	L29	10.6925MHz
R130	RX AM	L17	VCO Coil : 2,5 Volt @ 27.185MHz
RECEIVER
LF Output	RX FM	L6	Discriminator Coil

TRANSMITTER
TP3 (+) TP1 (-)	TX USB	VR9 (TR48 Bias)	50mA
TP3 (+) TP1 (-)	TX USB	VR10 (TR49 Bias)	50mA
TP3 (+) TP2 (-)	TX USB	VR11 (TR50 Bias)	10mA
TP1	TX SSB	VR7	Modulator Balance
Power Meter	TX AM	VR13	30 Watt AM Power
Deviation Meter	TX FM	VR6	+/- 2kHz FM Deviation
METER
RF Power Meter	TX AM	VR8	"30 Watt"
SWR Meter	TX AM	VR5

Microphone Connection

Pin	Description
1	Ground
2	Microphone
3	TX
4	RX
5	Program UP
6	Program DOWN

COMPONENTS

CX7925P Serial programmable PLL Frequency Synthesizer S042P Duble Balanced Mixer AN612 Balanced Modulator (SSB Modulator) TA7222AP Audio Power Amplifier NTM4558D Dual Operational Amplifire TA6324 Quad Operational Amplifire 2SC2166 RF Driver Transistor 2SC2312 RF Finale Transistor

Improved receive gain

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 2SC1675 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 2SC1675 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 2SC1675 (TR17) with an 2SC2999 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio.
Re-Adjust L7 and L8
The gain will improved with more than 6dB with the same signal to noise ratio.