Ramsey Electronics FZ-146 Specifications download pdf (Page 36)

FX 146 • 36

PROGRAMMING THE 'MINUS' OFFSETS

We showed the Plus offsets first to prepare you for the Minus offsets. The

offsets are entered into the FX synthesizer through the binary adders, U7-

10. Notice that we said adders and not subtractors; in binary there is 'no

such animal' as a subtractor. We must use the technique known as 'two's

complement addition' which actually performs a subtraction process! This

may sound complicated, but it really isn't. We simply find 'N' as usual, take

its 'two's complement' and program the result into the offset matrix. We'll

show you three detailed examples.

Don't be alarmed. If all you need is the standard 2 Meter band offsets, just

install the diodes in the offset matrix as clearly illustrated on your PC board.

Understanding the following information is essential ONLY for those who

need to program non-standard Minus or AUX offsets.

First we need to understand some rules for binary addition:

1) 0+0=0

2) 1+0=1

3) 1+1=0 and CARRY 1

(Carrying is done from right to left)

EXAMPLE 1: -600 KHz TX Offset

As for the +600 KHz offset, N= 600 ÷ 5 KHz = 120. However, this is the last

of Decimal numbers in this work. We'll have to work with Binary numbers

now. In brief, we set up the complement, or exact inverse of N in binary, and

then add 1. This will give us our two's complement that is needed for

programming into our offset matrix.

Binary code for N=120

Now, just INVERT all of the above 'bits':

1 1 1 1 1 1 1 0 0 0 0

Then, ADD 1:

1 1 1 1 1 1 1 0 0 0 1

This is our two's complement value which we program into our offset matrix.

You'll see these diodes in the position for -600 KHz TX offset.

Even though it appears that we are adding a huge N number to the original

transmitter frequency, the binary adders will follow the rules of binary

addition and provide the proper programming information to the PLL

synthesizer.

8192 4096 2048 1024 512 256 128 64 32 16 8

0 0 0 0 0 0 0 1 1 1 1

1 2 ... 31 32 33 34 35 36 37 38 39 40 41 ... 144 145

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Ramsey Electronics FZ-146 Specifications Page 36