Figure
06-4.
Harmonic Mixing Ranges
Harmonic
Number
N
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Next the VCO
is
stepped back into the passband and
a
new centering takes place. This second center fre-
quency
is
stored for later calculation of the harmonic number. Next the signal
is
stepped to the edge of the
passband position
it
had just left, and
it
is
centered. This center frequency
is
now compared to the first
edge of the
passband center frequency, and must be within
8
MHz. If
it
is
not within
8
MHz
it
will
be
assumed that the signal
is
moving, and the Band
4
program is exited.
Input Frequency Ranges
High Side Mixing
Low Side Mixing
(MHz) (MHz)
25,395
-
28,875 27,405- 31,125
30,675
-
34,875 32,685
-
37,125
35,955
-
40,875 37,965
-
43,125
41,235
-
46,875 43,245
-
49.1 25
46.51 5
-
56,875 48,525
-
55,125
51,795
-
58,875 53,805
-
61,125
57,075
-
64,875 59,085
-
67,125
62,355
-
70,875 64,365
-
73.1 25
67,635
-
76,875 69,645
-
79,125
72,915
-
82,875 74,925
-
85,125
78,195
-
88,875 80,205
-
91,125
83,475
-
94,875 85,485
-
97,125
88,755
-
100,875 90,765
-
103,125
94,035
-
106,875
96,045
-
109,125
99,135
-
1 12,875
101,325- 115,125
The IF frequency step size, caused by the VCO frequency step,
is
used to determine the harmonic number
by the following equation.
A
IF FREO. DUE TO VCO STEP
=
#(N)
HARMONIC SPACING
Where harmonic spacing
=
VCO step
size
X
12
CALCULATION ROUTINE
-
The calculation routine is used to find the approximate RF frequency Fin
in the following manner.
1.
Compute F'
=
12
N FVCO
2.
Center the YIG filter on the first IF
3.
Convert the binary YIG frequency to BCD
4.
Compute FIN
=
F'
f
FYIG (where FylG gives the approximate value for
the first IF).
5.
Compute a corrected VCO frequency using the equation:
FVCO
=
(FIN
'125)
1
(12N
'2)
Then tune the VCO with the corrected frequency and center the first IF frequency in the yig passband.
SHALLOW SEARCH
-
This routine
tests
for a signal in the IF passband. If a signal
is
present, the routine
is
exited. If a signal
is
not present, the routine will search an RF range of
GO
MHz (in steps of
200
kHz),
for the signal, and continues if a signal
is
found. If
a
signal
is
not found, the Band
4
program returns control
to the
supe~isor.
Scans by ArtekMedia © 2007
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