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6

Determining the leveled output

power

Figure 3-2 shows the input power

versus output voltage characteristics

for typical diode detectors from

Agilent Technologies. Using this

information, you can determine the

leveled power at the diode detector

input by measuring the external

detector output voltage. The range

of power adjustment is approximate-

ly –20 to +25 dB

External leveling with Option 1E1

signal generators

Signal generators with Option 1E1

contain a step attenuator prior to

the RF output connector. During

external leveling, the signal genera-

tor automatically holds the present

attenuator setting (to avoid power

transients that may occur during

attenuator switching) as the RF

amplitude is changed. A balance

must be maintained between the

amount of attenuation and the

optimum ALC level to achieve the

required RF output amplitude. For

optimum accuracy and minimum

noise, the ALC level should be

greater than –10 dBm.

For example, leveling the CW output

of a 30 dB gain amplifier to a level

of –10 dBm requires the output of

the signal generator to be approxi-

mately –40 dBm when leveled. This

is beyond the amplitude limits of the

ALC modulator alone, resulting in

an unleveled RF output. Inserting

45 dB of attenuation results in an

ALC level of +5 dBm, well within

the range of the ALC modulator.

NOTE For modulated carriers,

55 dB is the preferred attenuation

choice, resulting in an ALC level of

+15 dBm. This provides adequate

dynamic range for AM or other

functions that vary the RF output

amplitude.

To achieve the optimum ALC level

at the signal generator RF output

of –40 dBm for an unmodulated

carrier, follow these steps:

1. Press [Set Atten] > [45] > {dB}.

2. Press [Set ALC Level] > [5] > {dBm}. This sets the attenuator to 45 dB and the ALC level

to +5 dBm, resulting in an RF output amplitude of

–40 dBm, as shown in the AMPLITUDE area of

the display.

To obtain flatness-corrected power, refer to

Creating and Applying User Flatness Correction.

Figure 3-2.

Typical diode detector

response at 25° C.

Detector output voltage

10V

1.0V

100 mV

10 mV

1 mV

0.1 mV

–40 –30 –20 –10 0 +10 +20 +30

+20 dBV

+10 dBV

+6 dBV

0 dBV

–10 dBV

–20 dBV

–30 dBV

–40 dBV

–50 dBV

–60 dBV

–66 dBV

–70 dBV

–80 dBV

Detector input power, dBm

Linear

Asymtote

Square Law

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