Bird Model 61 Termaline Wattmeter, an RF absorption wattmeter used to measure RF power under non-radiating conditions. Manufacturer: Bird Electronic Corporation, Cleveland, Ohio, USA. Model: 61. Power Scales: 2.5 & 10 Watts (as indicated on the meter in the image, other scales might be available for this model). Impedance: 50 Ohms. Frequency Range: 30-500 MHz. Purpose: It functions as a 50-ohm coaxial termination for transmitters, providing a nearly reflectionless line termination, and is suitable for general field and laboratory use with CW, AM, and FM modulation envelopes
eBay