HP (Hewlett-Packard) 24A Manual De Usuario

Frequency modulation can be accepted from an external source at
the FM connector or can be internally generated by synthesizers
with Option 002. The damage level of the FM input is 

 V DC.

The input impedance is set to 

 A jumper on the All FM Driver

board allows you to change the input impedance to 
(See “Adjustments” in the Service Guide.) The FM sensitivity can
be scaled to either 100 

 1 MHz/V, or 10 MHz/V.

When internal FM is chosen (Option 

 the rate and deviation

are set by 

 in the FM 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
scale of the FM output depends on the FM deviation chosen. The

following table shows the scale versus deviation. The monitor menu
also lets you display the value of the FM deviation.

FM Coupling

Whether provided from an external source or generated internally

(Option 

 the FM system can be either AC or DC coupled. If

you choose AC coupled FM, you will be modulating a phase-locked
carrier. This is the specified synthesized operation. The modulation
rate must be 100 

 or greater. If not, the frequency changes

caused by the modulation are inside the phase-lock loop bandwidth
and the output will not be linear FM. For modulation frequencies
below 100 

 choose DC coupled FM. In this mode, the phase

locked loop is de-activated. This means that the synthesizer is
operating as an open loop sweeper. The synthesizer will not be
phase locked, and therefore, be aware that the phase noise and CW
frequency accuracy specifications do not apply.

 Message (Maximum Deviation)

The maximum FM deviation is limited by the following two
conditions:

l 

Maximum FM deviation must be less than 8 MHz and

l 

Maximum FM deviation must be less than n x 5 x FM rate

(refer to the “Frequency Bands” specification for the value of n).

The following chart shows the limits of each band given these two
conditions. For example, in band 1 at a 1 MHz FM rate, the FM
deviation must be less than 5 MHz.

n (1) x 5 x FM Rate (1 MHz)   5 MHz.