20 GHz Microwave Counter 2440

The Marconi Microwave Counter 2440 is a versatile, microprocessor-controlled frequency counter primarily designed for high-frequency (microwave) applications but offering a continuous measurement range starting from the audio band. It was engineered for speed, accuracy, and tolerance to complex modulated signals prevalent in communications.

Features and Architecture

1. Three-Channel Input System
The counter manages its extremely wide frequency range by routing the signal to one of three specialized input channels:

• Channels A & B handle the lower, direct-count frequencies. Channel A includes a switchable Low-Pass Filter to improve noise immunity when measuring low-frequency signals.
• Channel C employs the sophisticated Harmonic Heterodyne Conversion technique under microprocessor control to down-convert the microwave signal to an intermediate frequency (IF) that can be processed by the lower-frequency counting circuits.

2. High Modulation Tolerance
A crucial feature for communication applications, the 2440 can accurately measure the carrier frequency even when the signal is heavily modulated:

• FM Tolerance: Up to 30 MHz peak-to-peak frequency modulation.
• AM Tolerance: Up to 40% amplitude modulation depth.

3. Automatic Amplitude Discrimination
The counter includes automatic amplitude discrimination, which allows it to measure the strongest signal present on an input channel while ignoring adjacent, weaker signals or spurious responses. This is a form of inherent selectivity, simplifying measurements in crowded RF environments.

4. Frequency Offset Facility
A standard feature, the OFFSET function allows the user to program an offset frequency to be added or subtracted from the measured frequency. This is useful for testing transmitters or receivers where the actual operating frequency is shifted by a fixed intermediate frequency (IF).

5. Microprocessor Control
The instrument utilises a microprocessor to manage channel switching, auto-ranging, resolution settings, display functions, and both local keypad control and remote GPIB operation, making it suitable for both bench use and automated test systems.

Key Technical Specifications

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