Spectrum Analyzer Measurement Guide : Spectrum Analyzer : Amplitude Menu
Amplitude Menu
Amplitude Menu
Key Sequence: Amplitude
On older versions of firmware, the Auto Ref Level function may be accessible only from the Application Options Menu, and Units & Detection may appear as two separate submenu keys.
SPA Amplitude Menu
Auto Ref Level
Press this submenu key to adjust the position of a displayed signal so that it is approximately two divisions down from the top of the sweep window, if possible. When the key is pressed, the reference level is adjusted once. Auto Ref Level may turn off the low-noise front-end preamplifier, but does not turn it on. It has no effect on vertical scaling.
Reference Level
The reference level is the top graticule line on the display, and can be set from +30 dBm to –150 dBm. A value may be entered from the numeric keypad. Use the ± key to toggle between positive and negative values. After entering the value, press the dBm submenu key or the Enter key. The up or down arrow keys change the reference level in 10 dB steps, and the left or right arrow keys change the value by 1 dB. The rotary knob changes the value by 0.1 dB per click. The reference level value may be modified by the reference level offset value to compensate for an external attenuator or amplifier.
The scale can be set in 1 dB steps from 1 dB per division to 15 dB per division. The value can be changed using the keypad, the rotary knob, or the arrow keys.
Auto Atten On/Off
Input attenuation can be either tied to the reference level (On) or manually selected (Off). When input attenuation is tied to the reference level, attenuation is increased as higher reference levels are selected to make sure the instrument input circuits are not saturated by large signals that are likely to be present when high reference levels are required.
Atten Lvl
Press this submenu key and use the numeric keypad, the rotary knob, or the arrow keys to change the attenuation value.
RL Offset xx dB Ext Gain/Loss
RL Offset compensates for the presence of external input attenuation or gain. Enter a positive value to compensate for gain or loss, then press the appropriate submenu key (dB External Gain or dB External Loss). The new RL Offset value is displayed on the button.
Pre Amp On/Off
This submenu key turns the low‑noise front‑end preamplifier on or off. To ensure accurate measurement results, the largest signal into the instrument input when the preamplifier is turned on should be less than –40 dBm.
Units & Detection
Press this submenu key to open the Units & Detection Menu.
Units & Detection Menu
Key Sequence: Amplitude > Units & Detection
SPA Units & Detection Menu
Press this submenu key to select the amplitude unit: dBm, dBV, dBmV, dBµV, Volt, Watt, dBW, Amp, or dBA. When measuring Field Strength, values may be displayed in dBm/m2, dBV/m, dBmV/m, dBµV/m, Volt/m, Watt/m2, dBW/m2, A/m, dBA/m, or Watt/cm2. See Figure: Main Menu Keys. Press Back to return to the Amplitude menu.
Several detection methods tailor the function of the instrument to meet specific measurement requirements. There are often more measurement points across the screen than display points. The various detection methods are different ways of dealing with how measurement points are shown at each display point. The Detection submenu is illustrated on the lower left.
Peak: This method causes the largest measurement point to be shown for each display point, assuring that a narrow peak is not missed.
RMS/Avg: In the Preset case, when the VBW/Average Type is set to Linear, this method detects the average power of measurement points that go into the display point. When VBW/Average Type is set to Log, the traditional average of log(power), such as dBm, is displayed for the detector, as well as for VBW and trace average.
Negative: This method causes the smallest measurement point to be shown for each display point. It is especially useful in zero span, to see if the signal amplitude drops briefly. The method is also useful when looking at modulated signals, to see if some frequencies are not being used.
Sample: This is the fastest detection method because for each display point, only one frequency point is measured. Use this method when speed is of paramount importance and the possibility of missing a narrow peak is not important.
Quasi-peak: When this selection is made, resolution bandwidths and video bandwidths of 200 Hz, 9 kHz and 120 kHz are available. This detection method is designed to meet CISPR requirements.
Back: Returns to the Amplitude Menu.