The universal counter HM8123 features three high sensitivity inputs and allows the measurement of signals in the frequency range between DC and 3 GHz. Due to the high frequency of the internal oscillator of 200 MHz the time resolution is 10ns. Additional control and trigger functions are available via inputs on the rear of the instrument. There are inputs for arming, gate and trigger and outputs for gate and trigger signals.
 

1. POWER (pushbutton)
   Power switch, mains input connector on rear panel
2. GATE (LED)
   The GATE LED will be on for the duration of the gate time and synchronisation time, i.e. for the duration of one complete measurement.
3. REMOTE (LED and pushbutton)
   The REMOTE LED will be on if the instrument is under control via the interface. By pushing the REMOTE button operation will be returned to manual.
4. Display (LCD)
   Display of measurement results and additional information
5. ESC (pushbutton)
   Escape pushbutton (menu)
6. ENTER (pushbutton)
   Enter pushbutton (menu)
7. SELECT (pushbutton)
   Selects a menu or part thereof.
8. pushbuttons
   These arrow pushbuttons are used to control the menu and the parameters. Rotating knob Knob for entering parameters.
9. Rotating knob
   Knob for entering parameters
10. GATE TIME (pushbutton)
    Setting of gate time.
11. LEVEL B (pushbutton)
    Setting of channel B trigger level.
12. LEVEL A (pushbutton)
    Setting of channel A trigger level.
13. 1 : 10 pushbutton
    Input attenuator, total attenuation 100 times.
14. DC (pushbutton)
    Selects the coupling of the corresponding channel.
    Button DC lit = DC coupling
    Button DC dark = AC coupling
15. lope (pushbutton)
    This pushbutton selects the trigger slope. A lighted pushbut- ton indicates triggering on the negative slope, an unlighted pushbutton indicates triggering on the positive slope.
16. 1 : 10 pushbutton
    Input attenuator, total attenuation 100 times.

17. 50 Ω (pushbutton)
    This pushbutton connects an internal 50 Ω resistor to the input in order to allow operation in 50 Ω systems.
18. LP 50 kHz (pushbutton)
    This pusbuttons inserts a low pass filter in order to sup- press hf signals from interfering with triggering from low frequency signals.
19. TRIG (LED)
    Indicate triggered operation
20. INPUT A, INPUT B (BNC connectors)
    Input connectors for measuring signals DC to 200 MHz
21. INPUT C (SMA connector)
    Input for measuring signals 100 MHz to 3 GHz
22. INPUT A, INPUT B (BNC connectors)
    Input connectors for measuring signals DC to 200 MHz
23. TRIG (LED)
    Indicate triggered operation
24. INPUT C (SMA connector)
    Input for measuring signals 100 MHz to 3 GHz
25. RESET / V (pushbutton)
    Button with two functions:
    1. Pressing this button will stop any measurement, erase the display and start a new measurement.
    2. Setting the trigger level with the numerical keys 31, the entered value will be accepted with the unit Volts (V).
26. TRIG / GHz/s (pushbutton)
    Button with two functions:
    1. Pressing this button will start a measurement in ARMED mode.
    2. Setting the gate time with the numerical keys 31, the entered value will be accepted with the unit seconds (s).
27. HOLD / mV (pushbutton)
    Button with two functions:
    1. Pressing this button will freeze the display.
    2. Setting the trigger level with the numerical keys , the entered value will be accepted with the unit millivolts (mV).