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TM
11-5820-919-40-1
Transmit/Receive.
The
module
phase-locked  loop  (PLL)  and  will  stabi-
functions  identically  in
either  transmit
lize when the VCO oscillates at the
or  receive.
selected
frequency.
For  example,  at
16 MHz (which is halfway between 2 and
30 MHz), the VCO tune voltage is +5.8v
5-MHz LO.
The  5-MHz  temperature-
and the LO frequency is 91 MHz.
compensated  crystal  oscillator  (TCXO)  U1
The
generates  the  5-MHz  LO  signal.
Low  Frequency PLL .
The  low
5-MHz LO is routed to the multiplier U8
frequency  reference  of  the  PLL  begins
and  the  frequency  divider  U9  (via  ampli-
Frequency  divider
with  the  5-MHz  TCXO.
fier Q3).
The 5-MHz LO is also routed
U9  generates  two  frequency  standards,  1
A11
to  the  modulator/demodulator  at  J3.
and  10  kHz,  from  the  5-MHz  input.  The
other  frequencies  are  referenced  to  the
1-kHz  Standard  and  the  Frequency  Select
output  of  this  oscillator.
Logic  are  applied  to  the  low  frequency
phase lock U5.
The  low  frequency  phase
lock  generates  a  signal  that  is  between
The  5-MHz  output
70/80-MHz  LO.
0.0900  and  0.0999  MHz  (0.09XY,  where  X
of the crystal. oscillator U1 is applied
and  Y  correspond  to  1-kHz  and  O.1-kHz
to  multiplier  U8  where  70-80  MHz  har-
control  panel  digits).
Narrow
bandpass
monics  are  generated.
The  0.09XY  MHz  signal
a  few  examples.
filters FL2A and FL3B pass 70 and 80
mixes with 70.00 MHz from filter FL2B to
MHz,  respectively.  The  peak  amplitudes
produce  70.09XY  MHz  and  69.91xY  MHz.
are  adjusted  in  limiter  U7  and  outputted
The 69.91xY MHz is filtered out at fil-
to  three  filters  (FL2C,  FL3A  and  FL2B).
ter FL1A, leaving the 70.09XY MHz to be
When the LSB +28v select line is at +0v,
amplified  at  amplifier  AR3  and  refil-
filter  FL2C  receives  70  MHz  LO.  When
The  70.09XY  MHz
tered at filter FL1B.
the LSB +28v is +28v, filter FL3A
is then applied to the VCO.
Filter  FL2B
receives 80 MHz LO.
receives  the  70  MHz  (whether  LSB  +28v
is on or off) which is used in the 77-
High  Frequency  PLL.  The  70.09XY
105  MHz  voltage-controlled  oscillator
MHz enters the VCO U3 where it mixes
The 70 or 80 MHz is routed
(vCo).
with  the  output  of  the  voltage-
through  power  splitting  transformer,
controlled  oscillator  (between  77  and
T2,  and  impedance  matching  transformer,
The  upper  sideband  product
105 MHz).
T1,  to  the  modulator/demodulator.
of the mixing (77-105 + 70.09XY MHz)
is  filtered  out  at  the  band-pass  filter
The  frequency  passing
L3-7,  C18-22.
The 77-105 MHz LO
77-105 MHz LO.
This is
through  is  6.91-34.90  MHz.
is  discussed  in  paragraphs  2-62  thru
approximately  4.91  MHz  above  the  control
panel
frequency.
The  exact  frequency  of
2-62.  VCO.
the 77-105 MHz LO can be determined by
10-kHz  Standard.  The  6.91-34.90
MHz  signal  is  routed  through  prescaler
adding  75,000  kHz  to  the  control  panel
frequency.
This  frequency  is  generated
U4 to high frequency loop filter U2.
The  oscillation  fre-
by the VCO U3.
These  two  circuits  work  together  to
divide  the  6.91-34.90  MHz  input  between
quency of the VCO U3 is controlled by
The
691  and  3490  times.  After  the  division,
the VCO tune voltage (2.6 to 9v).
voltage  is  linearly  proportional  to  fre-
the  6.91-34.90  MHz  signal  is  about  10
At 2.6v the VCO output is about
kHz,  which  is  phase  and  frequency-
quency.
77 MHz, and at 9V it is about 105 MHz.
compared  against  the  .10-kHz  Standard.
Any  difference  will  cause  the  VCO  tune
The VCO tune voltage changes when a new
voltage  to  change.
frequency  is  selected  at  the  control
The tune voltage is part of a
panel.


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