HM8123 3GHz计数器是由德国罗德与施瓦茨公司生产的一款通用计数器。该计数器具有广泛的频率测量范围，从直流（DC）到3GHz，能够满足多种高频测量需求。它配备了三个输入通道，其中输入A和B的频率范围为DC至200MHz，输入C的频率范围为100MHz至3GHz。HM8123的输入阻抗灵活可调，输入A/B的阻抗可在50Ω和1MΩ之间切换，灵敏度为25mV；输入C的阻抗为50Ω，灵敏度为30mV。该计数器还具备10位分辨率（在10秒门控时间下），能够提供高精度的测量结果。此外，HM8123拥有九种测量功能，包括频率、周期、脉冲宽度等，并支持外部门控和警报连接。其外部参考输入/输出频率为10MHz，通过BNC连接。HM8123采用TCXO时基，温度稳定度为±0.5×10⁻⁶，而HM8123-X型号则配备了OCXO时基，温度稳定度更高，达到±1.0×10⁻⁸。该计数器还标配USB/RS-232接口，可选配IEEE-488（GPIB）接口，方便与其他设备进行通信和控制。其无风扇静音设计，使其在运行过程中噪音极低，为用户提供了良好的使用体验。目前，HM8123 3GHz计数器的市场价格因配置和销售渠道的不同而有所差异，一般在几万元人民币左右。

The HM8123 3GHz counter is a universal counter produced by the German company Rohde & Schwarz. This counter features a broad frequency measurement range, extending from direct current (DC) to 3GHz, which can meet various high-frequency measurement requirements. It is equipped with three input channels, with input A and B covering a frequency range from DC to 200MHz, and input C ranging from 100MHz to 3GHz. The HM8123 offers flexible input impedance adjustment. The impedance of input A/B can be switched between 50Ω and 1MΩ, with a sensitivity of 25mV. Input C has an impedance of 50Ω and a sensitivity of 30mV. The counter also boasts a 10-digit resolution (with a 10-second gate time), enabling highly accurate measurement results. In addition, the HM8123 has nine measurement functions, including frequency, period, pulse width, etc, and supports external gate control and alarm connection. Its external reference input/output frequency is 10MHz, connected via BNC. The HM8123 uses a TCXO time base with a temperature stability of ±0.5×10⁻⁶, while the HM8123-X model is equipped with an OCXO time base, offering higher temperature stability of ±1.0×10⁻⁸. The counter also comes with standard USB/RS-232 interfaces and optional IEEE-488 (GPIB) interfaces, facilitating communication and control with other devices. Its fanless silent design ensures extremely low noise during operation, providing users with a pleasant experience. Currently, the market price of the HM8123 3GHz counter varies depending on the configuration and sales channel, generally ranging from tens of thousands of yuan.