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NT and NR number calculation ( BK 77x )
“NT” and “ NR” are 16 bit binary numbers used to program the “PLL” N-divider in TX
and in RX mode.
“NT” and “NR” are entered into the radio in hexadecimal format. The “MSB” bit of “NT”
is used as a flag to program the RF output power : 1 = HIGH POWER , 0 = LOW POWER.
“NT” is calculated dividing the required TX frequency (KHz) by 12.5 ( 12.5 KHz
is the frequency programming step ).
“NR” is calculated from the required RX frequency (KHz) subtracting 21400
(21400 KHz is the first conversion intermediate frequency ) and then dividing by
12.5.
The “PLL” IC ( a FUJITSU MB15E03) when programmed for 64/65 prescaler
divide ratio, has an internal register ( “N” register ) where bit n° 6 of “N” word
must be set to 0 and ignored. To do this a 0 bit must be inserted as n° 6 bit into the
calculated “NT” and “NR” binary numbers.
A) “NT”
calculation
:
1) nT number : nT = TX
FREQ.
( KHz ) / 12.5
2) Write down nT in binary format ( 16 bit ).
3) Insert a 0 into nT as bit n° 6.
4) Write down the new binary number and eliminate the “MSB”
5) Convert in Hexadecimal format.
6) For “HIGH POWER” the MSB bit of the first Hex number must be set to “1”.
B) “NR”
calculation
:
1) nR number : nR = [ RX
FREQ.
(KHz) - 21400 ] / 12.5
2) Repeat point 2 to 5 as above.
EXAMPLE :
A) TX
FREQ.
= 433.7125 MHz
nT
NUMBER
= 34697 = 8789 H =
1000 0111 1000 1001
New bin. Number with 0 at n° 6 bit =
1 0000 1111 0000 1001
NT
NUMBER
( LOW POWER) =
0000 1111 0000 1001
=
0F09 H
NT
NUMBER
( HIGH POWER) =
1000 1111 0000 1001
=
8F09 H
B) RX
FREQ.
= 433.7125 MHz
nR
NUMBER
= 32985 = 80D9 H =
1000 0000 1101 1001
New bin. Number with 0 at n° 6 bit =
1 0000 0001 1001 1001
NR
NUMBER
=
0000 0001 1001 1001
=
0199 H
“CH” command format to program channel n° 2 on 433.7125 MHz ( transmit and
receive) , high power :
CH ( 1,8F09,0199 ) [ CR ] [ LF ]