If the transmitte r i s keyed without an antenna being conne c ted, o r , if
a high VSWR exi s t s in the antenna s ystem, the refl 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 rodu c e s DC
voltag e . Q 2 ll , (2 S C 3 7 2 Y ) c onducts with DC voltage applied through
VR2 0 5 cau s ing a d e c r e a s e in Q212 , ( 2 S C 3 72 Y )
1
s colle cto r cur r ent .
Thu s , the colle cto r volta ge of Q213 , ( 2 S A4 9 6) drop s , cau sing
Qll , (2 SD2 3 5 ) to d e c r ea s e cur r ent and s upply voltag e to the PA
amplifie r whi ch i s low e r ed to p r e vent damage to the tran s i s to r .
The thr e shold l evel i s s e t by VR2 0 5 . Thi s cir cuit i s al s o u s ed
to switch the output powe r down to 1 Watt when the HI -LOW switch
is s et to LOW . The amount of pow e r r e duction may be adju s ted
with VR2 0 6 .
The antenna chang e -ove r cir cuit c on s i s t s of 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 cuit c ons i s t s o f a timin g gene rato r and a gated
multi vib rato r . With the BURST switch a t the 110N11 po s ition , a
D C voltage i s applied to the tone bur s t c i r cuit . When the trans -
mitte r i s keyed , Q 214 , (2 SC 3 7 2 Y ) conduc t s and trig g e r s the one
s hot multivib rato r Q21 5 , (MC14 011 B ) . The other half of Q 2 1 5
g ene rate 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 mic rophone c i r cuit of the transmit
te r .
The tone frequenc y i s adjus table by VR2 0 7 , while the output level
(d eviation) is adju s table by VR2 0 9 and the bu r s t du r ation by
VR2 0 8 .
RE C EI VER S E C TION
The input s i gnal from the antenna i s fed through the low -pa s s filte r
c on s i s ting of 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 L212 to the F E T amplifi e r
QlOl , ( 3 SK 51 ) . The amplifi ed s ignal i s then appli ed through four s tage
high Q coax r e s onato r s to the fi r s t mix e r Ql 0 2 , ( 3 SK 51) . The u s e of
a dual gate F E T RF amplifie r to gethe r with high Q c o ax r e s onato r s ,
minimize s e ffe c t s of c ro s s modulation a nd othe r spuriou s r e s p o ns e s
while pr oviding a low noi s e fi gu r e fo r the r e c e ive r front end .
The 144 to 14 8 MHz s i gnal i s hete rodyne d with the fi r s t l o c al o s c ill
ato r and p roduc e s a 1 0 . 7 MHz fi r s t I F s i gnal . The fi r s t l o c al os -
cillato r is d elive r ed from the PLL (Pha s e Lo ck Loop) VCO c i r
cuit .
The fi r s t I F s i
&.
nal i s fed through a c ry s tal filte r XFlOl whi ch ha s
a pa s s band o f - 7 . 5 kHz , to the s e cond mixer Ql03 , ( 3 SK 4 0M )
whi ch produ c e s a 4 5 5 kHz s e cond 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 cal o s cillator Q104,
(2S C 3 7 2 Y ) . Ql 0 5 , (2SA 5 64 ) works as a switch whi ch di s conne c t s
the s upply volta g e t o Ql04 when the P L L c i r cuit i s unlo cked .
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Summary of Contents for FT-227R Memorizer
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