美國斯坦福SRS 射頻鎖相放大器SR844
25kHz—200MHz頻率范圍, 100s -30ks時間常數；6，12，18，24dB/倍頻程衰減,
內部或外部參考源；自動量程；存儲和調用9個儀器設備, 標準GPIB，RS—232接口
The SR844 is the widest bandwidth lock-in amplifier available. It provides  
uncompromised performance with a frequency range of 25 kHz to 200 MHz and up to 80 dB  
of drift-free dynamic reserve. It includes the many features, ease of operation, and  
programmability that you've come to expect from SRS DSP lock-in amplifiers.

 · 25 kHz to 200 MHz frequency range

 · 80 dB dynamic reserve

 · Time constants from 100 μs to 30 ks (6, 12, 18 or 24 dB/oct rolloff)

 · "No Time Constant" mode (10 μs to 20 μs update rate)

 · Auto-gain, -phase, -reserve and -offset

 · Two 16-bit DACs and ADCs

 · Internal or external reference

 · GPIB and RS-232 interfaces