Siemens - quartz Audio testing equipment

This is a case of synthesized/channel crystals for professional or military transceiver equipment (VHF/UHF).
Main features
● Format and markings: The modules are labeled CHAN. XXX (channel number) and show the corresponding frequency in megacycles/megahertz XX.X MC (a vintage term for Megacycles, equivalent to MHz).
● Frequency band: Based on the labels, they cover frequencies sequentially (in 0.1 MHz / 100 kHz steps), from the lower VHF range (around 70–80 MC) to above 99.8 MC (the 87.5–108 MHz or VHF broadcast/civil band).
● Operational use: Before the introduction of digital PLL frequency synthesizers (with displays and keypads), base, mobile, or repeater transceivers required a specific quartz crystal for each individual transmit or receive channel.
● Service/maintenance case: This complete, numbered matrix set was supplied to technical service laboratories, the armed forces, or telecommunications organizations (such as the police, fire departments, civil/maritime radio services, or repeater stations). It allowed field technicians to change or tune the equipment’s operating frequency by inserting the selected crystal into the appropriate socket.

The Dr. Steeg & Reuter crystal
• Manufacturer: Dr. Steeg & Reuter, Bad Homburg.
• Model: Type: FF5.
• Features: The holder is made of glossy black Bakelite, shaped with the company’s historic logo embossed at the top. The thick connection pins are typical of prewar and wartime German standards. This model was used both in precision radio equipment by Telefunken/Lorenz and as a frequency standard in research laboratories.