BAND 4 TRACKING
-
The tracking routine centers the second IF in the following range.
115 MHz
<2nd IF SIGNAL <I35 MHz
This routine is called from outside of the Band 4 program to track a signal. A test
is
first made to determine
if an IF threshold
is
present. If IF threshold
is
present
it
continues, if not the program returns to the super-
visor to start the locking process from the beginning.
This routine reads the second IF frequency and computes the new VCO frequency so that the second IF
is
in the range given above. A new YIG frequency is calculated and the VCO and YIG are "tuned" to produce
a new IF. A new FLO (frequency added to the second IF to produce the displayed frequency),
is
calculated.
The equation for this process
is:
The YIG frequency is:
NEW
FylG
=
2 (NEW VCO)
+
125 MHz.
PERFORMANCE TESTS
The Band 4 converter module is not field repairable. When a malfunction
is
suspected, its operation can be
checked from the front panel as follows:
IF AMPLIFIER Apply a -50
dBm signal to the diplexer porx (upper output jack) from 1.0 to 1.35
GHz. Output should be -3 dBm f3 dB as checked on a spectrum analyzer connected
to the IF output (lower jack).
LO SIGNAL Connect a spectrum analyzer to the diplexer port (upper output jack). Using the
fol-
lowing formula, set the VCO frequency between 440 and 500 MHz. The spectrum
analyzer should show the 12th harmonic of the VCO frequency (5.28-6
GHz). The
spectrum analyzer signal should be
+8 dBm minimum, and free of breakup and spuri-
ous signals to -30
dBc.
To convert from the desired
VCO
frequency to the PIA program number:
EXAMPLE
(440.75
MHz)
1. Round the desired frequency to a multiple of 50 KHz
(The resolution of the VCO frequency is 50 KHz).
........
2. Multiply the desired frequency (in MHz) by 5
440.75
X
5
=
2203.75
3. If the result contains no fractional part, go to step 8.
...................
4. Multiply only the fractional part by 16
.75 x 16
=
12
5. Add the result to the most significant digit from
step2..
.........................
MSDof2203.75=2-2+12= 14
6. Convert the result to hexadecimal
.......................
1410
=
E16
7. Replace the MSD from step 2 with the result from
step 6 and drop the fractional part
....................
2203.75
-+
E203
8. The two most significant digits are programmed to address 9822, and the two
least significant digits are programmed to address 9820.
Scans by ArtekMedia © 2007
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