- Capabilities and limitations of the AN/GRT–21 and AN/GRT–22
- The AN/GRT–21and 22 are designed to mount into what?
A standard 19-inch rack or cabinet.
- State the frequency range of both the AN/GRT–21and 22 transmitters.
AN/GRT-21 = 116.000 to 149.950 MHz; AN/GRT-22 = 225.000 to 399.975 MHz.
- How many channels are available for use in the VHF and the UHF transmitters?
VHF = 680; UHF = 3,500.
- At what temperature does the thermal protection actuate?
85o C.
- Theory of operations
1. What determines the frequency accuracy and stability of the transmitter set?
The oscillator synthesizer.
- Name the modules that make up the APC circuit.
The power detector DC1, the A10, and the control RF/modulator A6.
- What does the APC voltage do if the forward power gets too high?
Varies the gain of the A10 to normalize it.
- State the purpose of the E/L relay when operating the transmitter in the 10-watt mode.
The E/L relay has no purpose when operating in the 10-watt mode.
- Why does the UHF multiplier contain one more stage of amplification than the VHF version?
Because the fourth harmonic is weaker than the second harmonic.
- State the purpose of the transmitter tune/operate switch.
To protect the tunable filter during the tuning operation.
- What happens if the VSWR exceeds 3:1?
The E/L relay is energized and the LPA is bypassed.
- Why are we concerned with removing the RF from the E/L relay when it energizes?
Momentarily removing the RF prevents arcing between the contacts of the relay.
3–2. Linear Power Amplifiers
- Linear power amplifier basic block diagram theory of operation
- What is the purpose of the linear power amplifier?
To amplify the 10-watt output of the exciter to 50 watts.
- State the purpose of C1 and L1 in the A4 module.
To filter ripple out of the 2000VDC.
- In the A5 module, what are the LPA FWD and RVS power sensor voltages used for?
They are applied back to the exciter A6 module where they are used to develop the APC voltage and to detect VSWR.
- State the purpose of the LPA tune/operate switch.
It decreases the exciter RF output to less than 10 watts out and it prevents the E/L relay from energizing.
