How frequencies are converted to prom bits

The VCO oscillator is first divided by a counter which is some multiple of 63 times. Then it is further divided by some multiple of 64 times and compared with the reference frequency.

The formula for a stable phased lock loop is

- 64 * A + 63 * B equals Frequency / Reference

where

A is a value between 1 and 63

B is a value between 1 and 1023

Example:

A prom contains an A of 9, a B of 456, and reference of 5 kHz.

9 x 64 + 456 x 63 = 29304

29304 times 5 kHz. = 146.52 MHz Voile.

Conversely, one often starts with a frequency, not with prom values.

Divide 146.52 MHz by 5 kHz to get 29304 for the dual modulus system.

Now determine A and B.

But you can't easily find A and B with your calculator.

How many 63's and 64's are in 29304? Use your computer and try this

Simple BASIC program

- for B = 1 to 1023

- for A = 1 to 63

- if B * 64 + A * 63 = 29304 then Print A,B
next A

next B

The proms in Syntor, MCX-100, and Syntor X radios hold -

- Sixteen bits of A and B information

- Lets just look at the typical data in a prom -
Address 00 01 02 03 04 05 06 07 Values B 6 0 6 4 0 D 3

B664 Defines the frequency. 466B Reverse order 0100 0110 0110 1011 Convert to binary - 0100 0110 0110 101110 bits for B and 6 bits for A - B = 0100011000 = 280 Complement the lsb A = 101010 = 42 Complement the lsb 64 x A + 63 x B = 20328 Basic dual modulus algorithm 20328 x 5 = 101640 Multiply by 5 kHz reference 101640 + 322560 = 424200 Add UHF prescaler 424.200 + 21.4 = 445.6 MHz Add IF 21.4

- What are the other 8 bits - D 3?

- They select proper VCO subrange, Reference, front end and prescaler, depending on which radio.
- Syntor X radios additionally hold tot, pl, scan, and priority channel data.
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