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Amplitude modulation can be accepted from an external source at
the AM connector or can be internally generated by synthesizers with

Option 002. The damage level of the AM input is 

 

V DC. The

input impedance of the AM connector is 

 A jumper on the 

ALC board allows you to change the input impedance to 2 

 (See

“Adjustments” in the Service Guide.) The AM can be scaled either

linearly at 100% per volt or exponentially at 10 

 per volt.

When internal AM is chosen (Option 

 the rate and depth are set

by 

 in the AM menu. The waveform menu provides a choice

of sine, square, triangle, ramp, or noise waveforms. The monitor
menu lets you output the internally generated modulation waveforms
to the rear panel AM/FM OUTPUT connector. The AM output is
scaled the same as it is generated, either 

 or 10 

 This

connector can drive 

 or greater. The monitor menu also lets you

display the value of the AM depth.

UNLVLED Message

The maximum leveled output is limited by the synthesizer’s
maximum leveled output power specification. (Individual synthesizers
may be capable of greater leveled output power; the unleveled
message indicates the actual limit.) Amplitude modulation adds to
and subtracts from the reference RF power level. If an 
message appears on the display, you may be trying to modulate
beyond the synthesizer’s maximum output power capability.

OVRMOD Message

The maximum AM depth is limited to approximately 90% by the
detector’s ability to sense low power levels. If you try to amplitude
modulate too deep without using deep AM mode (explained later),
you will see an 

 message displayed on the message line. Also,

if you modulate below -20 

 ALC level without using deep AM

mode or below -50 

 with deep AM or search ALC mode, you

will see an 

message.

Dynamic Range

The ALC and attenuator combination (when an optional attenuator

is present) are automatically set by the synthesizer to keep the ALC
in its most accurate range (0 to -10 

 This is called the coupled

 operating mode.

For applications where modulating across an attenuation switch point

is undesirable, you can uncouple the attenuator and manually set the

power level of the ALC and the attenuator.

For example, setting the power level to 0 

 in coupled mode will

give an ALC level of 0 

 and 0 

 of attenuation. In uncoupled

mode, the attenuator can be set to 10 

 and the ALC to 

 

giving 0 

 output power and greater AM depth potential. The

ALC can now be varied over its entire range and the attenuator
remains at a fixed level.