Can We Subtract 512 From 864 - Ramsey Electronics FX-440 Manual

Even though there are 16 matrix positions to program, there are some
, shortcuts to make your job easier for normal ham band operation. Let's
_
look at the upper and lower band edges for the 440 MHz band:
, Band
FREQ. N 32K 1K 512 8 4 2 1 Edae
420. 00 33, 600 1 0 O O 0 O 1 1 O 1 O O O O O O Bottom
450.00 36,000 1 0 0 0 1 1 0 0 1 0 1 O 0 O 0 O Top
446.00 35,680 1 0 0 0 1 0 1 1 0 1 1 0 0 0 0
O
Simplex
Notice that the values of the highest 4 positions are the same throughout
the band. We still must program in those six positions but we only need
to calculate for the remaining 12 (2048 through 1 ).
Let's look again at the programming of 446.00 MHz Simplex, where N
=
35,680. First, we see that the 32K position is always programmed with a - -
diode and that the 16K through 4K positions never have a diode installed.
Let's put that fact to practical use:
1. We will always install a diode in the 32K position. This
gives us an 'initial' N value of:
32,768
2. This number can be used to ST ART programming ANY frequency
within the Amateur 440 MHz Band. We need only add additional
diodes in the 2048 through 1 positions for the various channels
within the band.
3. We determine these additional diodes by the same ·Descending
Attempted Subtraction,• that we used above for studying the
programming of 446.0 MHz Simplex, a process which you can do -
in your head, with scratchpaper, or on the FX-440 Programming
Worksheet.
Let's
do
an example:
1. We're already familiar with the right answer for 446.0 simplex, let's
use it again.
N
=
446000 ..;- 12.5
=
35,680
2. Since we have already installed a diode in the 32K position, our 'initial'
N is 32, 768. The N we need is 35, 680.
3. We now figure the difference between the N needed and the 'initial' N:
35, 680 • 32, 768
=
2, 912
4. Now, using the •Attempted Subtraction• technique, find the remainjng
binary value to be programmed.
Can we subtract 2,048 from 2,912? YES (Therefore: 2048 diode)
2,912 - 2,048
=
864
Can we
~ubtract
1,024 from 864? NO (Therefore: NO 1,024 diode)-
Can we subtract 512 from 864? YES (Therefore: 512 diode)
864 - 512
=
352
Assm. 54 FX-440