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Cobra 2000GTL Alignment


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Alignment Instructions

CAUTION: Use isoloation transformer or observe polatity when connecting test equipment. Maintain line voltage at 120V AC. Allow 15 minute warm up period. Adjustments made with 13.8V DC input. Connect low sides of test equipment to ground unless specified otherwise. Connect 50 ohm dummy load to antenna input before keying transmitter. Connect Microphone.

Synthesizer PLL

Test Equipment Transciver Adjust Remarks
Input of freq counter to TP13 (IC1 pin 8) CH19 Check for 10.240MHz
Input of oscope to TP10 CH19 AM L21 Adjust for maximum RF. RF 3.4V p-p typical
Input of DC meter to TP9 CH40 AM L19 Adjust for 3.00V. Check for appx 2.00V on CH 1
Input of oscope to TP1 CH19 AM L20 Adjust for maximum RF. (190mV p-p typical)
Input of freq counter to TP1 CH1 AM L23 Adjust for 34.7650MHz +20Hz
same as above CH1 USB L59 Adjust for 34.7665MHz +20Hz
same as above CH1 LSB L22 Adjust for 34.7635MHz +20Hz
Input of freq counter to TP10 CH1 AM Check for .790MHz (790KHz)
Input of freq counter to TP3 CH19 USB CT2 Adjust for 7.8015MHz +5Hz -0Hz
same as above CH19 LSB L30 Adjust for 7.7985MHz +0Hz -5Hz
Input of freq counter to TP14 (IC3 pin 7) CH19 AM xmit L31 Adjust for 7.800MHz +5Hz
Input of freq counter to TP15 (FET 1 GATE 1) CH19 AM Check for 7.3450Mhz
Input of freq counter to antenna input CH1 AM xmit VR5 Adjust for 26.9650MHz

Receiver

Connect a AC VTVM or AF wattmeter across speaker voice coil. Adjust volume control to obtain suitable indication. Set generator output low enough to preven AGC limiting. Preset controls as follows unless otherwise noted:

  • RF GAIN MAX
  • Voicelock Midrange (centered)
  • Squelch Min
  • NB OFF
  • ANL OFF
  • Tone Maximum clockwise
Test Equipment Transciver Adjust Remarks
Output of signal gen thru .01uF to TP16 (TR15 Emitter) 7.8000MHz no modulation CH19 USB L14,L12,L10,L9,L8,L7 Adjust for maximum output
Output of signal gen thru .01uF to TP15 (FET Gate 1) 455KHz 1KHz @ 30% modulation CH19 AM L15,L13,L3 Adjust for maximum output
Output of signal gen thru .01uF to antenna input. 27.1850MHz 1KHz @ 30% modulation CH19 AM L6,L5,L4 Adjust for maximum output, readjust L7,L8,L9,L10,L3,L13,L15 for maximum
Output of signal gen thru .01uF to antenna input 27.1850MHz 1KHz @ 30% modulation input of oscope to TP17 (D2 Cathode) CH19 AM L1,L2 Set generator output for 10DB signal to noise plus noise ratio of receiver. Inject a 100pps, 1uSec pulse width signal at antenna input. Switch NB on and adjust for maximum plulse amplitude. (8.2V peak typical)
Output of signal gen thru .01uF to antenna input. 27.1850MHz 1KHz @ 30% modulation, output 100uV CH19 AM VR1 AM SIGNAL METER, Adjust for S9 on signal meter
Output of signal gen thru .01uF to antenna input, 27.1860MHz no modulation output 100uV CH19 USB VR2 SSB SIGNAL METER, Adjust for S9 on signal meter

Transmitter

Connect a 25 watt dummy load to antenna connector

  • Be sure to check TX freq and power on all active channels after alignment
Test Equipment Transciver Adjust Remarks
Input of RF wattmeter to antenna input CH19 AM L47,L48,L46,L45,L38 Adjust for maximum RF output
Input of specturm analyzer or harmonic meter to antenna input CH19 AM L36 Adjust for Minimum at 54MHz (2nd harmonic)
Input of RF wattmeter to antenna input. no modulation CH19 USB Dynamike MINIMUM VR4 CARRIER BALANCE, Adjust for MINIMUM RF output
Input of RF wattmeter to antenna input, insert a 0-500mA DC meter at TP3. no modulation CH19 USB VR9 DRIVER BIAS, Adjust for 30mA idle current
Input of RF wattmeter to antenna input, insert a 0-500mA DC meter at TP7 no modulation CH19 USB Dynamike MINIMUM VR8 FINAL BIAS, Adjust for 60mA idle current
Input of RF wattmeter to antenna input, inject a two tone 500mV audio signal at mic input CH19 USB Dynamic Maximum VR11 SSB ALC, Adjust for 11.5 watts PEP RF output maximum
Input of oscope or modulation meter to antenna input, inject a 1KHz tone at 20mV audio signal at mic input CH19 AM Dynamike Maximum VR12 AM AMC, Adjust for 100% modulation maximum
Input of RF wattmeter to antenna input CH19 AM dynamike minimum VR10 AM CARRIER POWER, Adjust for 4.0 watts RF output maxium
Input of oscope or modulation meter to antenna input. injuect 1KHz audio signal at mic input set gen output to produce 100% modulation CH19 AM Dynamike maximum VR7 MOD METER, Adjust for 100% on Mod scale of meter
Input of RF wattmeter to antenna input CH19 AM dynamike minium VR6 RF POWER METER, at 4.0 watts of RF power adjust for RF PWR Meter agrees with RF wattmeter

Frequency Counter

Test Equipment Transciver Adjust Remarks
Input of oscope to TP504 (IC512 pin 5) CH19 AM Voicelock midrange counter/tme counter L501 Adjust for maxium then rotate core 1/2 turn clockwise
Input of oscope to TP502 CH19 USB L502 Adjust for maximum RF
Input of oscope to TP502 CH19 AM voicelock midrange COUNTER/TIME Counter CT501 Adjust for 27.1850 on counter display

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