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President Harrison CB-Radio


ALIGNMENT PROCEDURE


Receiver Section


Test equipment required:
Power Supply: 13,2 VRF Signal GeneratorSSVM Sinad MeterAudio Generator
AF Power MeterAF Distortion Meter8 ohm Load

StepSettingConnectionAdjustAdjust for
1RX Sensitivity
Mode: Receive
Volume: Fully clockwise
Squelch: Turn to clockwise
Channel: 19
SSG: 27.185 MHz, 1 uV(-107 dBm), AM 30% modulation
Connect RF Signal Generator to external ANT-jack. Connect SSVM Sinad Meter and Distortion Meter across External speaker out jack with 8 ohm dummy load.T501
T502
T504
T503
Adjust the parts of tuning circuit with observing AMD (AutomaticDisMeter) indicates 20 dB SINAD in AM-mode, and adjust output level of RF-SSG until speacker output level reaches about 500 mWatt (2.0 Volt)
2RX Sensitivity
Mode: Receive
Volume: Fully clockwise
Squelch: Turn to clockwise
Channel: 19
SSG: 27.185 MHz, 1 uV(-107 dBm), AM 30% modulation
Connect RF Signal Generator to external ANT-jack. Connect SSVM Sinad Meter and Distortion Meter across External speaker out jack with 8 ohm dummy load.T001Adjust for maximum indication on SSVM.
3Squelch adjustment
Mode: Receive
Squelch: Tight
Channel: 19
SSG: 27.185 MHz
1 kHz mod., 2,815uV (-47dBm), 30% mod.
Connect RRF SSG to ANT-jack. Connect AF Power Meter and Distortion Meter across ext-speaker with 8 ohm dummy-loadVR501At each mode, Adjust the point until the audio appeared on oscilloscope
4Signal meter adjustment
Mode: Receive
Volume: 500 mWatt
Squelch: Counterwise
Channel: 19
SSG: 27.185 MHz, 100 uV (-67 dBm), No mod.
Connect RF signalgenerator to external ANT-jack. Connect AF Power meter and Distortion Meter across external speaker jack with 8 ohm dummy load.VR301Adjust so that the 9`th LCD-Bar display on the LCD-meter.


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 KTC3880 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 KTC3880 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 2SC3142 transistor that has higher gain and lower noise characteristic. Replace the KTC3880 (Q501) with 2SC3142 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio receive.
Re-Adjust T501 and T502
The gain will improved with more than 3dB with the same signal to noise ratio.