T Heory O F Opera Tion - Yaesu MEMORIZER FT-227R Instruction Manual

The bl o ck di a g r am and th e c i r cuit de s c ription that follow s will p r o vid e
you with a b e tte r und e r s tanding o f thi s tran s c e ive r .
emati c di a g r am fo r c i r cuit d e tail s .
The tran s c e ive r con s i s t s o f a tran smitte r , and a d ouble c onve r s i o n
s up e r hete r odyne r e c e ive r utilizing a di gital pha s e l o ck l o o p s yn ­
the s ize r , c apable o f ope r ating on any o f the 8 0 0 channel s within
the f r e quency r ang e of 144 to 14 8 MHz .
ploy e d th r oughout and c o mpute r theo ry i s utilized fo r fr e quency
i
s e le c t on . The tr an s c eive r i s d e s i gned to op e r ate from a 1 3 . 8
Vol t s - 1 0 % ne g ative g round pow e r s our c e .
T R ANSMI T T ER
The tran s mitte r p r odu c e s a F r e quency Modul ated (F M ) s i gnal .
aud i o s i gnal from the mi c r o phone is s e t to a p r o p e r level by VR 2 01
and amplifi ed by Q 2 01 , Q 2 0 2 and Q 2 0 3 , (2 S C 3 7 2 Y ) .
put f r om Q 2 0 2 i s c oupl ed to th e I D C (In s tantane ou s D e viation C o n ­
t r o l ) c i r cuit whe r e both p o s i tive and ne gative p e a k s a r e clipp ed by
diod e s D2 01 and D 2 0 2 , (1Sl 5 5 5 ) .
fi e r Q2 0 3 i s fed thr ou gh a l ow -pa s s filte r whi ch a tt e nuate s f r e ­
que nc i e s abo ve the s p e e ch r ang e c au s ed by th e clipping at the l e vel
s et b y the de viation c ontr ol po te
nominally s e t fo r a d e via ti o n o f - 5 kHz .
appli e d to a pha s e modulato r va r a cto r diode , D 4 01 , (I SV5 0 ) whi ch
va ri e s the fr e quency o f the 1 0 . 7 MHz c r y s tal contr o ll ed o s c illato r ,
Q 4 01 (2 S C 3 7 2 Y ) . The fr e qu ency modulated 1 0 . 7 MHz s i gnal i s then
amplifi e d by a buffe r ampli fie r Q 4 0 2 , (2 S C 3 7 2 Y ) and then fed to
a b alanc e d mixe r c onsi s ting of Q 4 0 3 and Q 4 0 4 , (2 SK 1 9 GR) whe r e
the si gnal i s c o nve rted u p to 144 -14 8 MHz s i gnal b y mixing with
the 1 3 3 . 3 -13 7 . 3 MHz s i gnal d eliv e r e d fr om the V C O (voltage
c o nt r olled o s c illato r ) .
fed through the tune d c i r cui t s c on s i s ting o f T 4 04 - T4 07 to an am ­
plifi e r Q4 0 5 , ( 3 5K 4 0 M ) .
fr e quency by va r a c to r diod e s D 4 0 3 - D 4 0 6 o f who s e c apa citan c e
chan g e s i n a c co rdan c e with the D C output Volta g e f r om the P L L
c i r cuit . The 144 -14 8 MHz s i gnal i s the n amplifi e d by th e ampli ­
fi e r s ta g e s c on s i s ting of Q 2 0 4 , (2 5 C 5 3 5A ) , Q20 6 , (2 S C 2 0 5 3 ) , Q 2 0 7 ,
(2 S C 7 3 0 ) and Q 2 0 8 , (MR F 2 1 2 ) whi ch d e live r s 1 0 Watts of RF ene rgy
thr ou gh a diode switch and l ow pa s s filte r into a 50 ohm load .
D i od e s D 2 0 5 , and D 2 ll (1Sl 8 8FM ) r e c tify a small po r tion o f the R F
output and appli e s the r e sultant D C volta g e t o th e m e te r whi ch
indi c ate s r e lative p ow e r output f r om the transmitte r .
T h e D C output f r o m D 2 0 5 al s o i s d elive r e d
and Q2 1 0 , (2 S C 3 7 2 Y ) whi ch turn s the O N AI R lamp o n du ring the
transmi s s ion.

T HEORY O F OPERA TION

Solid s tate c i r cuitry i s em ­
The output f rom the la s t ampli ­
�.t
iomete r VR2 0 2 .
The s p e e ch s i gnal i s then
The output frcm the balanc e d mixe r i s
T 4 04 - T 4 0 7 i s tuned to the transmitting
- 1 4 -
R e fe r to the s ch ­
The audio out ­
Thi s c ontr ol i s
to
the lamp d rive r Q 2 0 9
The