Thumbwheel switch settings/divisor ratios.

TM 11-5820-695-35

7000 (corresponds to 5000.0 MHz) through 0000 (7000

(decimal 74 and 64) in 1A14A5 and 1A14A4

counts) until the unique number appears again in the

respectively. The unique number of 7464 establishes

registers. The cycle then repeats as described above.

the upper frequency limit for the divisor required for

dividing the if output from 1,A-14A2 ((2) below). When

(b)

Note that any divisor (D) can be

the number 7464 is decoded, the control circuits reset

the registers to an initial condition and the registers are

calculated by adding 540 to the number (N) preloaded

preloaded with the count set by the thumbwheel switch

into the registers and multiplying by 2 (D = 2 (N) + 540).

settings. After the preloading sequence, the if signal

For example, for a thumbwheel switch setting of 4400.0

causes the registers to count down to zero. The next

MHz, the number preloaded into the registers is 4000.

pulse produces the divide-by-N pulse output from

The divisor is calculated as follows: 2(4000 + 540) =

1A14A6. The pulse width of the divide-by-N output-is

2(4640) = 9080.

equal to 40 periods of the if output signal whose

sinewave frequency is between 14.1075 MHz and

(c)

The following tables list the thumbwheel

23.525 MHz depending upon the rf output frequency of

switch settings with corresponding closed switch

1A14A2. The registers in 1A14A5 contain the most

contacts (fig. 5-13) and the resulting decimal numbers

significant bits and will reach their unique number

which are loaded into the associated registers.

(decimal 74) before the registers in 1A14A4 have

reached their number (decimal 64).

(2) Thumbwheel switch settings/divisor ratios.

Variable frequency dividers 1A14A4 and 1A14A5 divide

the 14.1875 to 23.5625 MHz if output frequency from

1A14A2 by a number from 9080 to 1.5080 depending

upon the thumbwheel switch settings. The 14.1875 MHz

to 23.5625 MHz if output frequency is divided down to

1.5625 kHz to accomplish phase-lock. For example, for

a thumbwheel setting of 5000.0 MHz, the required if

output frequency is 23.5625 MHz. At this frequency, the

variable frequency dividers divide the if output

frequency from 1A14A2 by 15080 (23.5625 MHz

16080 = 1.5625 kHz). The divisor is obtained by adding

the counts to reach the unique number, initialize, inhibit

and preload sequence count and the thumbwheel

settings (1 + 536 + 3 + 7000 = 7540). Multiplying the

count by two (2 x 7540 = 15080) supplies the divisor.

The count is multiplied by two because the frequency of

the if output is divided by two in 1A14A4 before it is

applied to the registers. The following subparagraphs

describe how a thumbwheel switch setting of 5000.0

MH7 produces a divisor of 15080 in the variable

frequency divider circuits.

(a)

For a thumbwheel switch setting of 5000.6

MHz, the 0.1 MHz, 1.0 MHz, and 10 MHz divider-by-ten

registers in variable frequency dividers 1A14A4 and

1A14A5 are preloaded with zeros. The divide-by-eight

ripple through registers are preloaded with zeros. The

divide-by-eight ripple through registers are preloaded

with the number 7 ((c) below). The countdown cycle

starts at 0000 (1 count), then counts down from 7999 to

the unique number of 7464 (536 counts), after this count

an initialize, inhibit, preload sequence takes place (3

counts) and the thumbwheel switch settings are loaded

into the registers. The registers then count down from

2-37