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President Lincoln CB-Radio


ALIGNMENT PROCEDURE


RECEIVER PORTION


Test equipment required:
Power Supply: 13,8 VDummy Load 8 ohmAF VTVMOscilloscope
HF SSG:28.000 MHz1 kHz30% Mod.

Preparation alignment:
NB SWOff
PA SWOff
Beep SWOff
VOLUMEMax.
RITMiddle position
ModeAM
SquelchMin.
DX/LOCDX
Frequency28.000 MHz

StepConditionAdjustmentProcedure
1AM
SSG 40dB
1 kHz Mod.
L101 L104 L113 L115 L105Alignment of sensitivity. Adjust coils for maximum reading on the AF VTVM.
2AM
SSG 66dB
1 kHz Mod.
VR102Alignment of Squelch. Set Squelsch to maximum. Adjust VR102 so that the squelch just breaks.
3AM
SSG 46dB
No Mod.
VR101Alignment of S-meter. Adjust VR101 so that "9" LCD just lights on.
4FM
SSG 1 mV
1.5 kHz Dev.
L401Adjust L401 for maximum reading on the AF VTVM.
5AM
SSG 1 mV
Noise Gen.
L203Adjust L203 for maximum reading on the AF VTVM. Noise Generator output: 50 Hz SQ wave 2 V P-P.



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 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 (Q101) with an 2SC2999 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio.
Re-Adjust L101
The gain will improved with more than 6dB with the same signal to noise ratio.