Ramsey Electronics FX Series Manual page 26

particular frequency and its "N" number:
1. Descending Subtraction (see Programming Worksheet)
2. Printed reference lists (see Popular 2 Meter 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.
Notice the values of the highest 6 positions are the same throughout the
band. We still must program in those six positions but we only need to
calculate for the remaining 10 (512 through 1) to program any 220 MHz
band frequency desired. The simplex calling frequency of 223.5 MHz is the
demonstration and alignment standard for the FX-223 model.
"N" is quite easy to determine:
"N" for 223.500 MHz =
The placement of diodes in the Programmable Offset Matrix follows the
same binary number principles as used for frequency programming. This
matrix is connected to the 16 programming inputs of 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 1 bit to 8K range provides plenty of flexibility for non-
standard channel spacing.
U7 through U10 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 8K offset position goes
to B1 of U7 and the 8K frequency programming position goes to A1. 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 silk-
screened on the PC board itself. Assembly Stage H explains the theory
behind these positions. 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 straightforward "2's Complement" binary
addition. See Stage H for examples.
Stage M: Microphone Amplifier and PTT Circuit
= 44,700