英国(tti)数字频率计TF930的技术说明： 

Frequency, period, pulse width, frequency ratio 
duty cycle, and event counter modes
DC to 3000MHz range, 0.001mHz resolution
High impedance measurement up to 125 MHz

TF930 - 3GHz Universal Frequency Counter

  Frequency, period, pulse width, frequency ratio 
    duty cycle, and event counter modes
  DC to 3000MHz range, 0.001mHz resolution
  High impedance measurement up to 125 MHz
  AC or DC coupling, 1M/50Ohm selection, polarity invert
  Switchable attenuator, threshold control
  Noise filter for low frequency measurements
  Selectable measurement time; display hold function
  Large 10 digit display with full range of annunciators
  Internal rechargeable batteries for portable use
  USB interface provides full remote control and readback