Cobra PR-3850 User manual

PR-3850 Alignment instructions
Any repairs or adjustments should be made under the supervision of a
qualified radiotelephone technician.
I TRANSMITTER
1.Power Supply Voltage
The Power supply voltage should be set for 6.0VDC measured at the radio
during transmit. Periodically check the power supply voltage during the
alignment procedure.
2.Frequency Setting
A. Connect a frequency counter or Communications Service Monitor to the
Antenna through an RF power attenuator (10 watt minimum rating,
20 dB minimum attenuation).
B. Depress the PTT switch.
C. Adjust the VC1 trimmer capacitor such that the output frequency is
equal to the channel frequency with a maximum error of +/- 200 Hz.
D. Release the PTT switch.
3. Output Power Alignment.
A. Set the power supply voltage for 6.0VDC.
B. Connect a Communications Service Monitor or a wattmeter and dummy load
to the antenna connector.
C. Depress the PTT switch.
D. To be convinced for2.0 Watt output power with a maximum error of +/-0.3 Watt.
E. Release the PTT switch.
4. Deviation Adjustment.
A. Connect an audio generator to the microphone jack(JK1). The audio frequency
Should be set at 1 KHz.
B. Connect an FM deviation meter or Communications Service Monitor to the
antenna connector through an RF power attenuator (10 watt minimum rating,
20 dB minimum attenuation). Set the monitor to read peak deviation.
C. Depress the PTT switch.
D. Adjust the audio generator level 100 mV rms.
E. Adjust R79 for +/- 2.2 KHz maximum deviation. (With CTCSS tone)
F. To be convinced +/- 2.0KHz without CTCSS tone.(1.5KHz dev. 20dB up)
G. Release the PTT switch.

II RECEIVER
NOTE:
Insure that the proper channel has been selected before preceding with the
alignment procedure.
1. Power Supply Voltage
The proper voltage for testing is 6.0 VDC.
2. Receiver Alignment
A. Connect an RF signal generator or Communications Service Monitor to the
antenna connector.
B. Connect a SINAD meter and oscilloscope across the speaker terminals.
C. Set the output level of the RF signal generator for -47 dBm. The generator should be set
for +/- 1.5 KHz deviation of a 1 KHz tone.
D. Set the audio output level for 0.6 Vrms. by adjusting volume.
E. Reduce the output level of the RF signal generator for produce a 6-12 dB
SINAD indication.
III. WEATHER:
1. Power Supply Voltage
The proper voltage for testing is 6.0 VDC
2 weather
Alignment:
A. Connect an RF signal generator or Communications Service Monitor to the
antenna connector.
B.Connect a SINAD meter and oscilloscope across the speaker terminals.
C.Set the output level of the RF signal generator for -47 dBm. The generator should be
set for +/- 3 KHz deviation of a 1 KHz tone.
D.Set the audio output level for 0.6 Vrms. by adjusting volume.
E: educe RF output level to equal or less than –118dBm with condition of SIND=12Db.