
42-16 Time and Frequency
excellent resolution and allow very small frequency corrections to be made. For example, 1 μHz resolu-
tion
at 10 MH
z
al
lows
in
stantaneous
fr
equency
co
rrections
of 1 × 10
−13
. In addition, allowing the local
os
cillator
to fr
ee
ru
n
o
en
re
sults
in be
tter
pe
rformance
th
an
th
e
VC
O
me
thod,
wh
ere
un
expected
sh
is
in t
he
c
ontrol
v
oltage
c
an
p
roduce
u
nwanted
a
djustments
i
n
t
he
o
utput
f
requency
.
A rea
sonably
go
od
me
tric
to us
e
wh
en
ev
aluating
GP
SDO
pe
rformance
is it
s
fr
equency
st
ability
at τ=
1
da
y,
as es
timated
wi
th
AD
EV
. St
ability
of 1 × 10
−13
or less at τ = 1 day normally indicates a device of high
qu
ality,
an
d
ma
ny
(b
ut
ce ...