ACCEPTANCE TESTING
6-23
Internal phase modulation
Specification
Range:
Up to 10 radians in 0.01 radian steps
Accuracy:
Better than
±
5% at 1 kHz
Distortion:
Less than 3% at 1 kHz modulation rate
Bandwidth:
±
3 dB, 100 Hz to 10 kHz
Test equipment
Description Minimum
specification Example
Modulation meter
Minimum frequency 20 MHz
Aeroflex 2305
+ distortion option
Test procedures
(1) Connect the test equipment as shown in Fig. 6-9.
(2) Set the UUT to
[Carrier Freq.]
21,093,750.1 Hz
[RF Level]
0 dBm
[
Φ
M]
10 rad.
(3) Measure the phase modulation on the modulation meter which should read 10 rad
±
0.5 rad.
Internal phase modulation flatness
(1) Connect the test equipment as shown in Fig. 6-9.
(2) Set the UUT to
[Carrier Freq.]
21,093,750.1 Hz
[RF Level]
0 dBm
[
ΦΜ
]
10 rad
[Select
Source: F4]
1 kHz.
(3) Set the modulation meter to measure FM with the 50 Hz - 15 kHz LF filter selected.
(4) Measure deviation on the modulation meter and calculate phase modulation using the
formula:
Φ
M = FM dev (Hz)
mod
freq
1
(Hz)
(5) Select the modulation source frequencies as shown in Table 6-16 using
[Select Source: F4]
on the UUT, then enter the frequency.
(6) Measure the deviation on the modulation meter for each modulation frequency and calculate
the phase modulation for each step using the formula in (4) above.
(7) Using the figure recorded in (4) as a reference, calculate the change in response at each
modulation frequency using the formula:
20 log10 Figure recorded in (6)
Figure recorded in (4)
The change in response should be less than 1 dB with respect to 1 kHz.
(8) Reset the modulation frequency on the UUT to 1 kHz.
(9) Using the modulation meter set to
Φ
M, select DIST and measure the distortion which must be
less than 3%.
Table 6-16 Modulation source frequencies
Modulating frequency (Hz)
100 1,000
10,000
300 3,000
1 No allowances need be made for the modulation frequency accuracy since it is derived from the crystal reference oscillator in the UUT.