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


Block Diagram


Adjustment

Test equipment required:
Power Supply: 13,8 VFrequency CounterDummy Load 50 ohmOscilloscope
RF Power MeterDC AmperemeterRF SSGAF SSG

Preparation alignment:
FineMid.
ClarifierMid.
SQ GAINMax.
AF GAINMax.
RF GAINMax.
MIC GAINMax.
NB/ANLOff
MID Band, Ch. 19Frequency: 27.185MHz
Reading PointConditionAdjustmentProcedure
PLL
IC8 #4RX AML2110.2400MHz
IC8 #4RX USBL2210.2425MHz
IC8 #4RX LSBL2310.2375MHz
D32TX AML2710.6950MHz
D32TX USBL2810.6975MHz
D32TX LSBL2910.6925MHz
R130RX AML17VCO Coil : 2,5 Volt @ 27.185MHz
RECEIVER
LF OutputRX FML6Discriminator Coil
TRANSMITTER
TP3 (+) TP1 (-)TX USBVR9 (TR48 Bias)50mA
TP3 (+) TP1 (-)TX USBVR10 (TR49 Bias)50mA
TP3 (+) TP2 (-)TX USBVR11 (TR50 Bias)10mA
TP1TX SSBVR7Modulator Balance
Power MeterTX AMVR1330 Watt AM Power
Deviation MeterTX FMVR6+/- 2kHz FM Deviation
METER
RF Power MeterTX AMVR8"30 Watt"
SWR MeterTX AMVR5

Microphone Connection

PinDescription
1Ground
2Microphone
3TX
4RX
5Program UP
6Program 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.