The VTG MFJ Antenna Bridge Model MFJ-204B is a precision tuning tool for ham radio enthusiasts working in the HF band. This compact and lightweight unit features switchable frequencies and a handy on/off switch, making it easy to use with a variety of ham radio transceivers. The product comes with manuals and operates on a 9v voltage, making it a convenient and versatile accessory for fine-tuning your antenna for optimal performance in the 1.8-30 MHz range. Tested Battery clip needs to be glued to case
eBay