EFJohnson 9800 SERIES User Manual

4-5

February 2001

Part No. 001-9800-001

4.3.5 DETERMINING SYNTHESIZER COUNTER 

DIVIDE NUMBERS

Overall Div No. (K) = VCO freq ÷ .050

Example: 813.4875 ÷ .050 = 16,269.75

“A” Divide No. = 64 x Fraction (Integer K ÷ 64)

Example: 16,269 ÷ 64 = 254.20312

Fraction 254.20312 = 0.20312
64 x 0.20312 = 13

“N” Divide No. = Integer [K ÷ 64] – A

Example: Integer 254.20312 = 254

254 – 13 = 241

Fractional-N Div No. = (Fraction K) x 8

Example: Fraction 16,269.75 = 0.75

0.75 x 8 = 6

To isolate a receiver problem to a specific 

section, check the DC and RF voltages shown on the 
schematic diagram.

With UHF models only, the front end filter 

frequency shift inputs on U800, pins 6 and 7 should be 
as follows (L = 0V, H = 5V):

To isolate a transmitter problem to a specific 

stage, check the DC and RF voltages shown on the 
schematic diagram.

4.6.1 DIGITAL CIRCUITS

Because of the complexity and dynamic operation 

of the digital portion of the audio/logic board, 
servicing may be difficult. Special test equipment and 
knowledge of the operating software are usually 
needed to isolate a problem. Therefore, if a problem is 
suspected with the digital circuitry, it may be best to 
first make sure that the proper supply voltages are 
present and then replace the audio/logic board.

4.6.2 ANALOG CIRCUITS

The analog circuits on the audio/logic board can 

be checked by measuring the AC and DC voltages 
shown on the schematic diagram.

430-440 MHz

H

H

440-450 MHz

L

H

450-460 MHz

H

L

460-470 MHz

L

L

470-480 MHz

H

H

480-491 MHz

L

H

491-502 MHz

H

L

502-512 MHz

L

L