Cobra 148 GTL-B

Printed Circuit Board PTBM122DOX

Preset to channel 40, mode USB, clarifier centered.

The Mode in brackets ( ) indicates which mode the radio should be in.

PLL Circuit

Reading Point	Adjustment	Description	Value
IC1, pin 3	-	Check for 10.240MHz +/- 50Hz	10.240MHz
IC4, pin3	CT6	(USB) AM/USB Carrier oscillator	10.695MHz
IC4, pin3	CT5	(LSB) LSB Carrier oscillator	10.692MHz
TP2 (IC2, pin 4)	CT2	(USB) AM/USB offset oscillator	20.105MHz
TP2	CT1	(LSB) LSB offset oscillator	20.1035MHz
TP3	T1	0utput to RF local oscillator	37.660-38.100MHz for CEPT
TP1	VCO-Coil	VCO DC Voltage (DONT ADJUST IF WORKING OK!)	1.2 Volts @ channel 40 (27.405MHz) +/-0.5V

Preset to USB, channel 20, inject 2400Hz, 10mV audio signal.

Adjustment	Description	Value
T2	VCO Mixer Output	Maximum RF output power / best signal on oscilloscope at TP3
T3	VCO Mixer Output	Maximum RF output power / best signal on oscilloscope at TP3 (check even on channels 1 and 40)
T4	Transmitter Output	Maximum RF power output
T5	Transmitter Output	Maximum RF power output
L16	Transmitter Output	Maximum RF power output
RV4	Final Bias (Q7)	Connect DC Voltmeter to Q7 base (junction of C55, R34, L13) adjust for 0.70V
RV13	SSB Modulation	inject 2 tones, 500Hz and 2400Hz, at 10mV, adjust for 12 Watt pep
RV7	Carrier balance	Check / Adjust for NO Carrier on both LSB and USB
RV15	AM Output Power	Remove injected audio, Adjust for 6W carrier, a lower power level may be required to attain full modulation.
RV14	AM Modulation	Return to single 2400Hz tone @7mV, adjust for 92% modulation (see note above)
RV6	RF Power Meter	Adjust to match actual RF power

Preset to channel 20, USB, clarifier centered, NB/ANL turned off, RF gain set to maximum.

Be ready to inject a RF signal with an RF signal generator.

Adjustment	Description	Value
RV8	SSB AGC	??
T6	RF Input	Inject RF signal of 27.205MHz, 1KHz, 30% modulation, (keep the level low to prevent AGC action), adjust for maximum on radios signal meter / audio level at speaker (as measured with a scope or AF-VTVM)
T7	RF Input	as above.
T8	RF Input	as above.
T9	1.F.	10,7MHz, as above.
T10	1.F.	10,7MHz, as above.
T13	AM IF	455kHz, as above.
T14	AM Detector	455kHz, as above.
T11	SSB IF	455kHz, as above, also set for maximum audio output.
T12	SSB Detector	Set for maximum audio output.
T6, T7		turn both approx. 1/4 of a turn clockwise
RV10	AM S-Meter	Set RF signal generator to inject a 100uV signal, 1KHz, 30% modulation signal, adjust for "S9" in radios signal meter .
RV9	SSB S-Meter	Remove audio from RF signal generator, set for "S9" on radios signal meter.

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