In receive mode the first mixer heterodynes the antenna signal with VFO injection. In transmit mode the first
mixer functions as a balanced modulator with carrier oscillator injection and Mic. amp. input. In both modes the
first mixer output is at the intermediate frequency (I.F.) of 5520 kHz.
In receive mode the second mixer functions as a product detector with carrier oscillator injection. Its output
couples audio frequencies to the receiver audio system. In transmit mode the second mixer heterodynes the I.F.
signal with VFO injection. Its output is now at the transmit frequency, and is coupled through tuned circuits to
preamplifiers, driver stage, and power output amplifier.
Oscillator switching is accomplished with four F.E.T.'s, resulting in very low intercoupling between oscillators.
4-6. TRANSMITTER BROADBAND CIRCUITRY
The amplifier stages of the transmitter provide full power output over the 1.8 to 21.4 MHz range, about 60%
power at 29.7 MHz, and require no tuning. Tuned circuits between the second mixer and transmitter amplifier
module select the desired mixer product and reject the unwanted products. These tuned circuits are band switched
and provide full coverage of each band. They are double tuned and over coupled, requiring no further adjustment
after being factory set.
Harmonic output from the Power Amplifier is suppressed by a band switched two section low pass filter. This
filter is connected between the Power Amplifier output and antenna terminal. The low pass filters and Power
Amplifier are both designed for a 50 ohm load. It is important that the load be quite close to 50 ohms, non-
reactive, in order to operate at full rated power.
4-7. RECEIVER BROADBAND CIRCUITRY
The receiver input filters are band switched, and provide full band coverage without need for a panel peaking
control. In addition, the signal passes through the low pass transmitter filter, suppressing possible interference
from strong local VHF signals.
4-8. ALIGNMENT AND TROUBLESHOOTING
The overall chassis schematic diagram is Figure 4-15, and is placed at the end of this section to facilitate the
technician in matching the P.C. board schematics to the overall schematic. The individual P.C. board schematic
diagrams arc shown in Figures 4-4 through 4-14. Voltage measurements and parts list are located adjacent to the
P.C. board schematics.
4-9. VOLTAGE CHARTS
All voltage measurements must be made with a meter having at least 10 megohms input resistance. All D.C.
voltages are designated by the + (positive) symbol. Voltage figures not having the + symbol are RMS values of an
AC voltage. Refer to the following notes when making any voltage measurements.
NOTES
1. RMS voltage measured with R.F. probe, and bandswitch in 7
MHz position.
2. Approximate RMS voltage with Mic. Jack input of .03
volts at 1000 Hz. Mic. Gain at maximum clockwise.
3. RMS voltage with R.F. probe, CW mode, Mic. Gain at
Maximum clockwise.
4. Full R.F. Gain, no signal input.
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