Ramsey Electronics FZ-146 Specifications download pdf (Page 25)

FX-146 • 25

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 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 2 Meter band

frequency desired. The simplex calling frequency of 146.52MHz is the

demonstration and alignment standard for the FX-146 model.

"N" is quite easy to determine:

"N" for 146.520 MHz = = 29,304

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

silkscreened 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.

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Ramsey Electronics FZ-146 Specifications Page 25