Theory Of Operations - Intek M-490 Plus Service Manual

Model No: 3390
Customer :

THEORY OF OPERATIONS

TRANSMITTER
A. RF Amplification
The output of double AMP Q301 is fed through tuning IFT L301 and L302 to the base of pre driver AMP
Q302. The output is then supplied through tuning circuit L303 to RF driver AMP Q303. The output of
Q303 is supplied with tuning circuit L304 and C317,C315,C21 and goes to the base of final RF AMP
Q304. The output of Q304 is supplied to the antenna through L-C tuning circuit.
B. Circuit for Suppression of Spurious Radiation
The tuning circuit between the output of final AMP Q304 and antenna, 4-stage "PHI" network L308,
C324, C1, C327, L311, C337, C333, L312, C328, C334, C338, L313 serves as a spurious radiation
suppressor . This network also serves to match the impedance between TX power AMP Q304 and the
antenna.
C. Circuit for Limiting Power
After finished all alignment, the constant voltage supply circuit limits the available power 4 W or slightly
less. RV1 and corresponding three transistors control supply voltage of RF amplifier and other circuits.
Tune all the trimmer parts for maximum indication of RF power meter and adjust RV1 to make 4 w
indication of RF power meter.
The tuning is adjusted so that the actual power is from 3.8 to 4.0 W. There are no other additional
controls for adjusting the TX output power.
D. Modulation Control
a. FM
The mic input is fed to mic audio amplifier IC KIA324 which drives modulation varicap diode
D403 in the VCO circuit. RV401 limits the incoming modulation audio levels to inhibit over modulation.
While reading the modulation factor on the modulation analyzing equipment, adjust
RV401 shall not exceed +-1.8 KHz/Dev. After 20 dB up from 1.25 KHz/1.2 KHz/Dev. Audio level
b. AM
Modulation signals are filtered with RC network and goes to the audio power AMP IC IC103 to make
nominal signal level to achieve wanted modulation. To control incoming audio signal, diode D203 and
corresponding ALC circuit limits the modulation shall not exceed +/-80% adjust RV201 +/-80%
modulation under 1.0 KHz AF 60% mod plus 20 dB of audio signal.
Created by:
For Stage:
Title
M-490 Plus
Approved by:
Release Date:
Drawring No:
Rev,Date:
Rev.No:
Page: 5 / 61