Wavetek 3001 Instruction Manual page 155

G ENER AL INFO RM ATIO N
Option 5 Incl udes the circ u it ry necessa ry to enable the
instrument to
b
e dr iven
b
y an exte rn al
r
efe ren ce frequ ency,
thus im proving the accuracy of t he sig nal ge nerator. The
r
eference input requirements are as follows :
FREQUENCY - 1, 2, 2.5, 5, or 10 MHz
ACCUR ACY -wit hin 1 ppm of above
f
r eq uencies.
LEVEL RANGE - 50 mV to 5 V (RMS)
IMPEDA NCE - 1
k
iiohm
INSTALLATION
To add
t
h is option to
t
he inst rument, fi r st
r
emove top and
bottom covers as explai n ed in Section 5.2 of this manual .
T h e module plugs into t h e open socket adjacent to the
Μ30-1/4 (r efe r to F ig ures 5-5 and 5-6) . The additional RF
ca bles conn ect t h e Μ39 to
t
h e Μ30-1/4 an d the instrum ent
rear p a nel .
OPERATIO N
W
hen an extern al signal is connecte d 2ο
t
he
r
ear-panel BN C
connector,
t
he instrument is ready to use with i n crease d
accuracy .
T h e front- pa n el ACCUR ACY lig hts should
In dicate
"E XT ERNAL"
unless
t
he FREQUENCY
VERN I ER ίs ουτ οf the CAL position .
T
HEORY OF OPERATIO N
T
he pu rpose of this circuit is 2ο ph ase lock the Crystal
R
eference in
t
he i nstrum ent to α
h
ig her accuracy reference.
The circ uit functions include: "ph ase
d
etection" to
OPTION 5
E XT ERN A L REFERE NC E
Compare
t
he variable frequ ency to the reference and
s
upply
α refe rence voltage, "h arm onic ge n e r ation" to allow the
exte rnal
r
eference to
b e any ο 1 seve r al frequ encies, "unlock
i nd ication" to tell the operator when this loop is unloc k ed,
and "reference monitoring" to
d
isengage this loop from this
i nstrument wh en
t
he refernce input is disconnected .
R
efer to Figure 815-1 for α b loc k diagram of t h e ci rcu it .
PHAS E
D
ETECTIO N
T he refe rence (10 MHz) inpu t to
t
he ph ase detector is
s upplied from an exte rn al source via the harmo n ic
generator. The signal is fe d
t
hrough e
p
ai r of inverters to
ma k e t h e sign al level m ore comp ati ble wit h the ph ase
d
etector. The variable (10 MHz) signal from
t
he voltage
controlled oscillator is fed
t
hrough
I
nverte rs for the same
reason. The ph ase detector output is filtered by an
integrator ci rcuit and app lied to α va racto r diode in the
oscillator in
t
he Crystal
R
eference module . The 40 MHz
oscillator frequ ency is divided by four and fed to the ph ase
d
etecto r. Α ce rtain voltage to the
V
CO will
t
un e the
variable input to
t
he phase
d
etector to the exact freque ncy
of the
r
eference input. If the variable input
f
requ ency
shifts hig h or low,
t
he ph ase
d
etecto r output voltage
changes and tunes
t
he va ractor oscillator in
t
he opposite
d
irection, thus kee ping the varia ble input locked to
t
he
r efe r ence in put.
UNLOC K
I
NDICATION
T h e i nteg r ator output (ph ase d
etection ci rcuit) is fe d to e
wi ndow
d
etecto r. When
t
his tuning voltage goes outside
t h e normal ope r ating range (too p
ositive or negative), α DC
voltage is
a
pp lied to
b
oth an L
E D on to p of the modu le and
to the flas her circuitry in
t
h e
M
odu lation Boa r d asse mb ly
to cause the front-panel ACCUR ACY ligh t to
f
lash.