The Marconi Atalanta was a British communications receiver designed for professional radio communications. It is an interesting piece of engineering, associated with the era when valve technology was still central to military, maritime and commercial wireless communications. It belongs to the generation of equipment designed for reliable communications rather than domestic broadcasting.
I bought one of these from GWM Radio, Worthing. It cost me £100 back in the 1970s. What a lovely receiver! Resolving SSB was easy, selectivity and sensitivity were great. The only let down was its weight! It took two of us to carry it upstairs to my shack. Once installed, it became my main HF communications receiver.
One point of interest was a bi-metallic strip situated near the oscillator section of the variable tuning capacitor. One plate mounted on the strip moved back and forth with temperature changes, moving closer or further away from the other plate. This acted as a capacitor. One plate was connected to ground and the other plate wired to the oscillator section of the tuning capacitor. This compensated for the changes in the tuning capacitor vanes due to room temperature.
Historical background
The Atalanta was introduced in the mid-1950s by The Marconi International Marine Communication Company. It was manufactured from approximately 1955 until 1967–68. Its principal purpose was to serve as the main communications receiver aboard ships and at shore-based marine radio stations.
Technical specifications
| Specification | Details |
|---|---|
| Model | Atalanta Type 2207C |
| Period | Approximately 1955–1967 |
| Receiver type | Single or dual-conversion superheterodyne |
| Frequency coverage | 15 kHz–28 MHz |
| Valves | 13, or 14 with optional muting circuit |
| Reception modes | AM, CW and MCW |
How good was the receiver?
The Atalanta was built as a serious professional receiver rather than an ordinary domestic radio. Some of its important features included:
- Multiple IF stages for good selectivity.
- Several selectable bandwidths.
- Mechanical filtering for narrow CW reception.
- Fine electrical tuning.
- A crystal oscillator for checking frequency calibration.
- Adaptability to different shipboard power supplies.
Its role aboard ships
The Atalanta was intended to be the main receiver in a ship's radio room. During the 1950s and 1960s, ships relied heavily on wireless communications for:
- Receiving weather forecasts.
- Receiving navigational warnings.
- Sending and receiving Morse messages.
- Communicating with coastal radio stations.
- Receiving maritime safety information.
- Maintaining contact with other vessels.
A ship's radio officer needed equipment that could operate reliably for long periods. The Atalanta was designed with this professional environment in mind. It was also suitable for shore-based marine radio stations.
One of the most interesting aspects of the Atalanta is its frequency conversion system. It did not use exactly the same conversion arrangement throughout its frequency coverage.
It employed:
- A single conversion system on certain lower-frequency ranges.
- Double conversion on other ranges.
- A first intermediate frequency of 700 kHz.
- A second intermediate frequency of 85 kHz.
The 85 kHz intermediate frequency was used to provide the receiver's final selectivity. This arrangement helped the designers achieve wide frequency coverage while maintaining useful selectivity.
Selectivity and tuning
The Atalanta had four selectable bandwidths, ranging from approximately 8 kHz down to 100 Hz. This was particularly useful when receiving Morse signals. The narrowest bandwidth used a mechanical filter, allowing unwanted signals close to the wanted signal to be rejected.
It also featured a 700 kHz crystal oscillator for checking the calibration of the frequency scale. Another useful feature was its marine band-spread tuning, with six HF marine bands having dedicated calibrated scales.
The valves
| Valve | Function |
|---|---|
| 2 × EF85 | RF amplifier stages |
| ECH81 | First mixer |
| EF85 | First local oscillator |
| ECH81 | Second mixer and oscillator |
| W77 | First IF amplifier |
| Z77 | Second IF amplifier |
| D77 / EB91 | Detector |
| ECH81 / X719 | Beat frequency oscillator |
| 6060 / B309 / 12AT7 | Audio amplifier |
| N37 | Audio output |
| Z77 | Crystal calibrator |
| QS75/20 | Voltage stabiliser |
The optional muting circuit used another ECH81 or X719.
The power supply
One interesting aspect of the Atalanta is its power arrangement. The receiver required approximately 110 volts DC at 450 mA.
This supplied both the high-tension circuit and the valve heaters, which were connected in series. Depending on the installation, power could be provided by:
- 110V DC shipboard supplies.
- 220V DC through a suitable resistor unit.
- 115V or 230V AC using an optional internal power supply.
- 24V DC using a suitable external converter.
This made it particularly suitable for different marine electrical installations.