Yaesu MEMORIZER FT-227R Instruction Manual page 17

I f the tran s mi tte r i s keyed without an antenna being c o nne c ted, o r , if
a high VSWR exi s t s in the antenna s y s t e m, the r e fl e cted pow e r is de -
te c ted thr ough T 2 0 2 and a diode , D 2 0 8 , ( 1Sl 8 8FM) whi ch p r odu c e s D C
voltag e . Q 2 ll , (2 S C 3 7 2 Y ) c ondu c t s with D C volta ge applie d thr o u gh
VR2 0 5 c au s ing a d e c r e a s e in Q 2 1 2 , ( 2 S C 3 72 Y )
T hu s , the coll e c to r volta g e o f Q 2 1 3 , ( 2 S A4 9 6) d r op s , cau sing
Qll , (2 SD2 3 5 ) to d e c r e a s e cu r r ent and s upply volta g e to the PA
amplifie r whi ch i s l ow e r ed to p r e ve nt d a ma g e to the tran s i s to r .
The thr e shold l evel i s s e t by VR2 0 5 .
to switch the output pow e r down to 1 Watt when the HI -LOW switch
is s e t to LOW . The amount of pow e r r e du c ti o n may b e adju s te d
with V R2 0 6 .
The antenna chang e - ove r c i r cuit c on s i s t s o f switching o f diode s
D 2 0 6 and D 2 0 7 , ( MI 3 01) .
The tone bur s t c i r cui t c on s i s t s o f a timin g gene rato r and a gated
multi vib r a to r . With the BURST switch a t the 110N11 po s iti on , a
D C volta g e i s appl i e d to the tone bur s t c i r cuit .
mitte r i s keyed , Q 2 14 , (2 S C 3 7 2 Y ) c o ndu c t s and tri g g e r s the one ­
s hot multivib rato r Q 2 1 5 , (M C14 011 B ) .
g ene r ate s a tone s i gnal whi ch is amplifi e d by a buffe r Q 2 1 6,
(2 S C 3 7 2 Y ) and applied to the mi c r ophone c i r cuit of the tr a n s mi t ­
te r .
The tone f r e quenc y i s adjus table by V R 2 0 7 , while the output l e v e l
(d eviation) i s adju s tabl e b y VR2 0 9 a nd the bu r s t du r ati on b y
V R2 0 8 .
RE C EI VER S E C TI ON
The input s i gnal from the antenna i s fe d through the low - p a s s filte r
c on s i s ting o f Ll , L 214 , L 2 1 3 , Cl and C 2 4 3 -C 2 4 5 and the dio d e change -
ove r switch c on s i s ting o f D 2 0 6 , D 2 0 7 and L 2 1 2 to the F E T amplifi e r
QlOl , ( 3 SK 51 ) . The amplifi ed s i gnal i s the n appli ed th r ou gh fou r s ta g e
high Q c o ax r e s onato r s t o the fi r s t mix e r Ql 0 2 , ( 3 SK 5 1 ) .
a dual g ate F E T RF amplifi e r
minimize s e ffe c t s o f c r o s s modulati on a nd othe r s pu r i ou s r e s p o ns e s
while p r oviding a l ow no i s e fi gu r e fo r the r e c e ive r front e nd .
The 144 to 14 8 MHz s i gnal i s hete r o dyne d with the fi r s t l o c al o s c ill ­
a to r and p roduc e s a 1 0 . 7 MHz fi r s t I F s i g nal .
cillato r is d elive r ed from the P L L (Pha s e L o ck L o o p ) V C O c i r ­
cuit .
&.
The fi r s t I F s i nal i s fed thr ough a c ry s tal filte r XFl O l whi ch ha s
a pa s s band o f - 7 . 5 kHz , to the s e cond mix e r Ql03 , ( 3 SK 4 0M )
whi ch p r o du c e s a 4 5 5 kHz s e c o nd I F s i gnal by hete r odyning with
the 1 0 . 2 4 5 MHz output s i gnal of the s e c o nd lo c al o s c illator Q 1 0 4 ,
(2S C 3 7 2 Y ) . Ql 0 5 , (2SA 5 64 ) w o r k s a s a switch whi ch di s c o nn e c t s
the s upply volta g e t o Ql04 when the P L L c i r cuit i s unl o cked .
s coll e cto r cu r r ent .
1
Thi s c i r cuit i s al s o u s ed
Wh en the t r a n s -
T h e oth e r half of Q 2 1 5
to g e the r with high Q c o ax r e s onato r s ,
The fi r s t l o c al o s -
- 1 5 -
The u s e of