MOGlabs ARF021, Руководство пользователя

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Chapter 5. External modulation
5.2 Modulation gain
The modulation gain, which controls the modulation depth, is set
using the
GAIN
command. The gain is specified as a signed 32-bit
integer (default 0) in either decimal or hexadecimal, with a negative
value indicating the the modulation action is inverted
1
.
The range of gain values is shown in the table below. In principle,
modulation depth can also be decreased through the amplitude of
the input signal, but it is preferable to use the full
±
1 V dynamic
range to minimise discretisation error.
FM AM PM
Max gain (hex) 0x3FFF8000 0x3FFF 0xFFFF
Max gain (dec)
1,073,709,056 16,383 65,535
Step size 0.23 Hz 0.006% Max 0
.
0055
◦
Max modulation 250 MHz 100% Max 360
◦
Table 5.1:
Gain ranges for different modulation modes.
Based on these values and ignoring discretisation and saturation,
an applied voltage will have the following effective modulation:
Frequency:
df
= (0
.
23 Hz/V)
G
f
V
in
Phase:
dφ
= (0
.
0055
◦
/V)
G
φ
V
in
Amplitude (*):
dA ≈



(14 V/V)
G
a
V
in
for 421 -models
(2
.
6 V/V)
G
a
V
in
for 021 -models
(*): This expression assumes a 50 Ω load, and depends on the indi-
vidual unit power calibration. The actual output amplitude respects
the maximum power limit set by the
LIMIT
command. The availa-
ble modulation depth depends on the difference between the current
output power (
POW
) and the predefined limit (
LIMIT
).
1
Negative hexademical values are represented using two’s complement.