Ramsey Electronics FX-440 Manual page 26

There are several methods for quickly finding the required binary code
for a particular frequency and its • N • number:
1. Descending Subtraction (see Programming Worksheet)
2. Printed reference lists (see Popular 440 MHz Frequency Pairs)
3. Computer programs (see our sample BASIC program)
We recommend strongly that you fully understand how to make the
calculation yourself, because that is your ONLY means for checking the
accuracy of printed information, computer programs or the operation of
experimental programming circuits. Even though there are 16 matrix
positions to program, there are some shortcuts to make the job easier for
normal ham band operation. Consider the upper and lower band edges.
FREQ. N
=
32K >BINARY PROGRAMMING VALUES> 4 2
430. 000 34, 400 1 0 0 0 0 1 1 0 0 1 1 0 0 0 0 0
450. 000 36, 000
1 0 0 0 1 1 0 0 1 0 1 0 0 0 0 0
Notice the values of the highest 4 positions are the same throughout the
band. We still must program in those four positions but we only need to
calculate for the remaining 12 (204S through 1) to program any 440 band
frequency desired. 446.0 MHz is the national Simplex Calling Frequency
and, also the demonstration and alignment standard for the FX-440
model. • N • is quite easy to determine:
446000 (KHz)
"N" for 446.00 MHz
=
=
35,6SO
12.5 (KHz)
The placement of diodes in the Programmable Offset Matrix follows the
same binary number principles as used for frequencr programming. This
matrix is connected to the 16 programming inputs o U6 through the four
4 bit binary adders (U7-U10). Fewer programming positions are provided
on the board simply because there is no practical use for extremely large
or very tiny offsets. The 2 bit to SK range provides plenty of flexibility for
non-standard channel spacing.
U7 through U1 O are called • 4 bit" binary adders because they each can
handle four binary addition operations. For each bit, there are A and B
inputs and one S (sum) output. Examine the schematic diagram closely,
and you will see that all the frequency programming lines are connected
to "A" inputs and all offset lines go to "B" inputs. Notice further that the
binary positions of both matrixes correspond to each other exactly: the
SK offset position goes to 81 of U7 and the SK frequency programming
position goes to A 1. Their sum appears at S1 (pin 1) and goes to U6. And
so forth for all the other binary programming positions.
The programming for receive mode and standard repeater offsets is
silkscreened on the PC board itself. For the theory behind these
positions, please refer to Assembly Stage H. The
+
RPT
"N"
numbers
are calculated in the same way as for the Frequency Programming
matrix. -RPT, RECV and other "minus" offsets are calculated by
Ref. 24
FX-440