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In the JRC JMA-9923 radar system, the NMA-1252 is the high-power Modulator Unit. It is the “power plant” of the transmitter, responsible for converted stored electrical energy into the high-voltage pulses required to fire the magnetron at a peak power of 25 kW.
The NMA-1252 operates as a solid-state switching system. Its primary job is to generate a precisely timed, high-voltage square wave pulse. When the radar is in “Transmit” (TX) mode, the modulator takes a low-voltage trigger signal from the CMC-1205 control board and instantly steps it up to several thousand volts. This pulse “shocks” the magnetron into oscillating at X-band frequencies (approx. 9.4 GHz).
The NMA-1252 is an assembly that contains:
CPA-264 Modulator PCB: The logic heart of the unit. It controls the pulse width (how long the magnetron stays on) and the Pulse Repetition Frequency (PRF).
Pulse Transformer: A heavy-duty transformer that performs the final voltage “kick” from hundreds of volts to the $7.5\text{–}8.5\text{ kV}$ level.
Charging Circuit: A series of capacitors and inductors that store energy during the “off” time so it can be released instantly during the “on” time.
Heater Supply Circuit: Provides a steady $6.3\text{ V}$ to the magnetron’s filament. This is critical for thermionic emission; without this “warm-up,” the magnetron cannot produce RF energy.
| Feature | Specification |
| Model Number | NMA-1252 |
| Radar Output Power | 25 kW (Peak) |
| Output Pulse Voltage | $7.5 \text{ kV to } 8.5 \text{ kV}$ |
| Output Pulse Current | Approx. $8.0 \text{ A to } 10.0 \text{ A}$ |
| Magnetron Type | MG5436 (X-Band) |
| Pulse Repetition Frequency (PRF) | $400 \text{ Hz}$ to $3000 \text{ Hz}$ (range dependent) |
| Heater Output | $6.3 \text{ VDC/VAC}$ (Nominal) |
| Main Control PCB | CPA-264 Modulator Board |
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