76 N9912A FieldFox User’s Guide
Then External Gain
Enter a value using the numeric keypad, the ▲|▼ arrows, or the rotary knob
(positive for gain; negative for loss). Values less than 5 dB must be typed using
the numeric keypad. Then press Enter
ExtGain xx dB is shown at the top of the screen.
Attenuation Control
Both the RF Attenuation and Pre Amp functions control the power level into the
SA.
When too much power is present at the RF IN port, ADC Over Range appears
on the FieldFox screen. This does not necessarily mean that damage has
occurred, but that the measurement is probably compressed.
When high power levels are present at the RF IN connector, internal attenuation
can be switched in to keep the FieldFox receiver from compressing. At extremely
high power levels, use external attenuation to protect the internal circuitry from
being damaged.
The FieldFox can be damaged with too much power.
RF Damage Level: +27 dBm
DC Damage Level: ±50 VDC
The displayed power level is automatically adjusted for RF Attenuation. As the
attenuation value changes, the displayed power level should NOT change.
How to set Attenuation
The default Attenuation setting is 10 dB. This value can be changed from 0 to 31
dB in 1 dB steps.
Press Scale/Amptd.
Then RF Atten Auto Man.
Auto RF Attenuation is set by adjusting the Reference Level. As the Reference
Level is lowered, for example from –10 dB to –30 dB, the FieldFox assumes
that you are looking at low-level signals. The RF Attenuation value is
automatically lowered in 5 dB steps to allow low-level signals to be viewed.
The RF Attenuation value is never automatically lowered below 5 dB.
Man RF Attenuation is set manually. Enter a value using the numeric keypad,
the ▲|▼ arrows, or the rotary knob. Values less than 5 dB must be typed
using the numeric keypad. Then press Enter
#Atten xx dB is shown at the top of the screen. (#) means manual setting.
Preamplifier Control (Opt 235)
When very low-level signals are analyzed, an internal preamplifier can be used
to boost the signal level by approximately 22 dB. The gain of the preamp is NOT
adjustable. The displayed signal level is automatically adjusted for the increase in
system gain.
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