Axcera 430B, Руководство пользователя

Страница: 22 / 58

Axcera-430B Type Acceptance Report Test Report
February 2004 4-12
With the receive dipole antenna cut to 175.25 MHz, the cabinet radiation was also
checked, within very close proximity to the trays of the transmitter, and the received
level that was recorded, and is shown below, did not exceed a power density above
-6dBm:
Pr/A = 0.025 mw/cm
2
This level is far less than the current or proposed standard for safe radiation levels.
4.6 Frequency Stability
The output carrier frequencies are determined by the IF crystal oscillator, IF aural
oscillator, and the crystal oscillator/multiplier of the exciter. Because the IF aural
oscillator at 4.5 MHz is phase locked to the IF crystal oscillator at 45.75 MHz, the error
in visual/aural separation is very small.
All three oscillators and the related phase-locked loop circuitry were placed in a
temperature-controlled chamber and the temperature was varied from –30
° C to
+50 ° C. The chamber was slowly heated and the frequency was measured at 10 ° C
increments up to +50 ° C. The oscillators were allowed to stabilize at each temperature
before measurements were recorded.
Tables 4-10, 4-11, and 4-12 provide data on the individual oscillator frequencies; a
calculation of the output frequency error indicates that the output frequency of the
transmitter is well within the FCC tolerance for this service.
Table 4-10. Oscillator Data
TEMP ( °° C)
45.75-MHz
CRYSTAL
OSCILLATOR
4.5-MHz
AURAL
OSCILLATOR
(PHASE
LOCKED TO
45.75 MHz)
OVEN-
CONTROLLED
EXCITER
CRYSTAL
OSCILLATOR
(MHz)
VISUAL/
AURAL
FREQUENCY
SEPARATION
(MHz)
-30 45.750100 4.500011 81.124932 4.500011
-20 45.750061 4.500006 81.124968 4.500006
-10 45.750057 4.500006 81.124969 4.500006
0 45.750043 4.500005 81.124975 4.500005
10 45.750023 4.500003 81.124986 4.500003
20 45.750000 4.500000 81.125000 4.500000
30 45.749974 4.499998 81.125031 4.499998
40 45.749945 4.499994 81.125057 4.499994
50 45.749917 4.499996 81.125070 4.499996