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FX 146
•
36
PROGRAMMING THE 'MINUS' OFFSETS
We showed the Plus offsets first to prepare you for the Minus offsets. The
offsets are entered into the FX synthesizer through the binary adders, U7-
10. Notice that we said adders and not subtractors; in binary there is 'no
such animal' as a subtractor. We must use the technique known as 'two's
complement addition' which actually performs a subtraction process! This
may sound complicated, but it really isn't. We simply find 'N' as usual, take
its 'two's complement' and program the result into the offset matrix. We'll
show you three detailed examples.
Don't be alarmed. If all you need is the standard 2 Meter band offsets, just
install the diodes in the offset matrix as clearly illustrated on your PC board.
Understanding the following information is essential ONLY for those who
need to program non-standard Minus or AUX offsets.
First we need to understand some rules for binary addition:
1) 0+0=0
2) 1+0=1
3) 1+1=0 and CARRY 1
(Carrying is done from right to left)
EXAMPLE 1: -600 KHz TX Offset
As for the +600 KHz offset, N= 600 ÷ 5 KHz = 120. However, this is the last
of Decimal numbers in this work. We'll have to work with Binary numbers
now. In brief, we set up the complement, or exact inverse of N in binary, and
then add 1. This will give us our two's complement that is needed for
programming into our offset matrix.
Binary code for N=120
Now, just INVERT all of the above 'bits':
1 1 1 1 1 1 1 0 0 0 0
Then, ADD 1:
1 1 1 1 1 1 1 0 0 0 1
This is our two's complement value which we program into our offset matrix.
You'll see these diodes in the position for -600 KHz TX offset.
Even though it appears that we are adding a huge N number to the original
transmitter frequency, the binary adders will follow the rules of binary
addition and provide the proper programming information to the PLL
synthesizer.
8192 4096 2048 1024 512
256
128
64
32
16
8
0
0
0
0
0
0
0
1
1
1
1
FX-146
•
111
"N" for 146.52 MHz = 146520 ÷ 5 = 29,304
Now, install Programming Diodes at all YES positions and we're done!
The practical result from the preceding exercise is that we install diodes only
in the YES positions on the matrix. Compare these results with the diode
programming illustrated for 146.52 MHz Simplex on the schematic diagram.
If you do not yet understand EXACTLY what we did in this exercise and why,
Subtracting from N:
Remainders & Doodles
NO
YES
Position
Can you subtract 32768?
3
32768
Can you subtract 16384?
12,920
3
16384
Can you subtract 8192?
4,728
3
8192
Can you subtract 4096?
632
3
4096
Can you subtract 2048?
3
2048
Can you subtract 1024?
3
1024
Can you subtract 512?
120
3
512
Can you subtract 256?
3
256
Can you subtract 128?
3
128
Can you subtract 64?
56
3
64
Can you subtract 32?
24
3
32
Can you subtract 16?
8
3
16
Can you subtract 8?
0
3
8
Can you subtract 4?
3
4
Can you subtract 2?
3
2
Can you subtract 1?
3
1
Will this be a Simplex chan-
nel?
3
SIMP
Will Transmit be 600 KHz
LOWER than Receive?
3
- RPT
Will Transmit be 600 KHz
HIGHER than Receive?
3
+ RPT