This receiver is an exceptional value for a synthesized receiver covering any frequency between 216.000 and 222.000MHz with no gaps in coverage. This not only allows you to hunt with multiple birds transmitting at the same time, but multiple dogs also. The R-600A is supplied with a folding high gain, and very directional antenna which mounts directly to the receiver and rivals a Yagi in performance. No coax is required, allowing one handed operation. A standard 9 volt alkaline battery powers the unit and is easily changed using a fingernail. Not only is the R-600A extremely sensitive to hear the weakest telemetry signals, it also employs very effective filters to eliminate unwanted interference sources. The synthesized design provides excellent temperature stability with no drift in frequency settings. A four step attenuator allows full receiver sensitivity for longest range or reduced sensitivity for extremely close-in tracking to a few inches. The R-600A employs a large, full range, speaker for rich sounding loud audio. A very sensitive signal strength meter also doubles to let you know when the battery needs replacing. A rugged, light weight, aluminum case is standard as well as a 3.5 mm mono headphone jack and adaptor for the larger 1/4” headphone plugs. A standard circ., 5.5mm x 2.1mm, center positive, power jack allows the R-600A to be powered from an external 9-14VDC source.