Ramsey Electronics FX-440 Manual page 112

Stage H:
FREQUENCY PROGRAMMING:
Understanding and Building the Diode Matrix
The labeling of the 16 parallel programming inputs of U6 should have a
familiar ring to anyone with at least some understanding of computer
principles, which should include all of us by now. Even though our
desired "N" number is a five-digit decimal number, it is programmed as a
"16 bit" BINARY number.
Binary numbers can be as big as you like, but we get there by counting
on a base of two, either 1 or 0, yes or no, on or off. This is, of course, the
foundation for all digital circuitry.
The programming inputs of your FX transceiver synthesizer can be set
for any frequency in its range, using the correct "N" number, by means
of the diode programming provided with your kit, or with simple switches,
or by digital switching circuitry, or by a dedicated microprocessor circuit,
or by a control circuit controlled by the same computer you use for
packet, etc.
We will cover only the diode programming approach with some brief
suggestions on externally controlled switching. It is very intentional on
our part to leave innovative programming schemes up to FX transceiver
users, because there's no single best way to do it for everybody. Our job
was to break the price barrier on a practical, state-of-the-art UHF
transceiver and make it highly useful for most operating patterns.
You have easy front-panel selection of ANY 12 frequency pairs and never
need to buy a crystal. Nor should you ever need factory service. THAT is ·
what this transceiver is all about!
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 Band Pairs)
3. Computer programs (see our sample BASIC program)
We recommend strongly that you fully understand how to make the
•attempted descending subtraction" calculation yourself, because that is
your ONLY means for checking the accuracy of printed information,
computer programs or the operation of experimental programming
circuits.
Let's walk through the programming of 446.0 MHz, which is the national
Simplex Calling Frequency and is also the demonstration and alignment
standard for the FX-440 model. You'll see exactly what we mean by
"descending
att~mpted
subtraction.• Also, this is how the model BASIC
program for diode programming included in this book is structured.
Assm. 52
FX-440