Racal RA17C18

Description: The RA17C18 is a modified version of the RA17C12, featuring a delay-compensated IF amplifier and an additional IF output. It is designed for the North American market, utilizing BNC and SO239 connectors, with all fasteners having unified threads. The harmonic mixer (V4) is a 6AS6. The device does not include a BFO, and the IF bandwidth selector offers four positions: 13 kHz, 6.5 kHz, 3 kHz, and 1.2 kHz. Instead of a BFO, the receiver is equipped with a DC-coupled video output and a front panel DC Zero adjustment related to this output. The Shaper Level control adjusts a peak-level clipping circuit, which influences both the video and audio outputs. The accompanying photograph displays the solid-state power supply and the specialized IF amplifier module. Originally, the unit had a permanently attached mains lead and a voltage selector, but these were replaced (by the author, around 1982) with an input receptacle and two switched mains outlets for adapters. The 3-pole Belling-Lee connector used is no longer type-approved in the UK and is scheduled for replacement.

The RA17C18 receiver is a sophisticated piece of equipment designed for optimal performance in various radio frequency applications. The modification from the RA17C12 to the RA17C18 includes enhancements that improve signal processing and output capabilities. The delay-compensated IF amplifier ensures that signals are processed with minimal phase distortion, which is crucial for maintaining signal integrity, especially in applications requiring precise timing.

The addition of an extra IF output allows for greater flexibility in signal routing and processing. This is particularly useful in setups where multiple signal paths are necessary, such as in laboratory environments or complex communication systems. The choice of BNC and SO239 connectors is significant, as these connectors are widely recognized for their reliability and ease of use in RF applications.

The harmonic mixer, utilizing the 6AS6 tube, contributes to the overall performance of the receiver by enabling effective frequency conversion with low distortion. The absence of a BFO (Beat Frequency Oscillator) indicates a design choice that prioritizes clean signal reception over additional modulation capabilities, which may not be necessary for all applications.

The IF bandwidth selector's four distinct positions (13 kHz, 6.5 kHz, 3 kHz, and 1.2 kHz) allow users to tailor the receiver's response to specific signal conditions, enhancing versatility in various operational scenarios. The DC-coupled video output is a noteworthy feature, providing a direct signal for video processing applications, which can be critical in systems where visual representation of the signal is required.

The front panel DC Zero adjustment facilitates precise calibration of the video output, ensuring that users can maintain optimal performance levels. The Shaper Level control introduces additional functionality by allowing users to manage peak-level clipping, which is essential for preventing distortion in both video and audio outputs.

The modifications made to the power supply and mains connections reflect a commitment to modernizing the unit while maintaining its core functionality. The introduction of an input receptacle and switched mains outlets enhances the usability of the device, allowing for easier connection to various power sources without compromising safety or performance. The transition from the 3-pole Belling-Lee connector, which is no longer type-approved, to a more current standard will ensure continued compliance with safety regulations and improve the unit's operational reliability.

Overall, the RA17C18 is a well-engineered receiver that combines traditional design elements with modern enhancements, making it suitable for a wide range of applications in the field of electronics and communications.The RA17C18 is modified version of the RA17C12, having a delay compensated IF amplifier and an additional IF output. It is a North American version of the RA17, ie. , it uses all BNC and SO239 connectors, all fasteners have unified threads, and the harmonic mixer (V4) is a 6AS6.

It has no BFO, and the IF bandwidth selector has only four positions: 13KHz, 6. 5KHz, 3KHz, and 1. 2KHz. The receiver is instead equipped with a DC-coupled `Video` output, and a front panel `DC Zero` adjustment which relates to it. The `Shaper Level` control adjusts a peak-level clipping circuit, which affects both the video and audio outputs.

The photograph below shows the solid-state power supply and the specialised IF amplifier module. The set originally had a permanently attached mains lead and a voltage selector, but these were replaced (by the author, in ca. 1982) with an input receptacle and two switched mains outlets for adapters (the 3-pole Belling-Lee connector used is no longer type-approved in the UK and is scheduled for replacement).