Tektronix 7000 Series Manual page 18

T he d
elay time is selecte
d
with
t
he
fro nt p
anel DEL AY TIME OR EVEN TS
d
F
I NE DEL AY co ntrols .
F
or conve-
J
n
e nce, t
h e setting of the DELAY TIME
OR EVEN TS control is dis
p
laye
d
on th e
oscillosco
p
e crt readout.
The 7D11 internal cloc k
p
rovi
d
es an
acc u racy of - - 2
n
s (0 .5
ppm),
wh ic h is Τ
much more accurate than ca n be o b-
taine
d
from an analog
d
elaye
d
swee
p
time base . If accuracy greater th an 0.5
pp
m is re
q
uire
d
, th e 7D11 d
elay-by-
R P
Ι
time cloc k can be reference
d
to an ex-
ternal 1- MH z timing sta n
d
ard i n
p
ut Ι
t
h roug h
t
he ΕΧΤ 1 ΜΗΖ IN connector.
Delaye
d
Trigger
J
itter with
t
he d igital
d
elay is re
d
uce
d
to less tha n 2.2
n
s for
d
elay times as
Ι
lo n g as 22 ms .
1η
t
he delay-by-events
m
ode (see
F
ig .
Ί--- Delay Time -j,
19), the 7D10 or 7D11 counts trigger
events from an extern al source, either
p
eriodic or a
p
erio
d
ic, an
d
generates α
d
elaye
d
trigger once α p reselecte d
co un t
h
as been reac h e
d
. Two signals
are re
q
uire
d
to o
p
erate the 7D10 or
7D11 in the
d
elay-by-events mo
d
e . One
signal is in
p
ut throug h
t
he ΕΧΤ TRIG IN
F
ig . 20 . Ra
d
ar
p
ulse timing measurement .
co nn ector an
d p
rovi
d
es t h e events to
be cou n te
d
. The ot her signal is in
p
ut
throug h
t
h e EVEN TS START T R IG ΙΝ ,-------------
. on nector an
d
tells the delay u nit wh en
G
B
p
ELAY-ΒΥ-ΤΙΜΕ
to begin counting . B ot h connectors
this instability can become excessive
h ave in
d
e
p
en
d
ent trigger controls .
an d ma k e t he d is
p
lay unuseable Wh en
MEASUREMENTS
.
50 MH z
Events ca n be counte
d
at rates up to
using d elay-by-events, the oscillosco
p
e
, Wh en the selecte
d
num ber of
is triggere
d
at or near the event to b
e
events
h
as been cou nte
d
, α signal is
observe
d
, rather than at th e en
d
of α
Testing α ra dar system is one exam
p
le
d
elivere
d
to both
t
he DLY'D TRIG O UT
fixe
d
time
d
elay . Timing signal j
itter
h
as
of
h
ow more accurate measurements
connector an
d
i
n ternally to the main-
no effect on th e
d
is
p lay.
can be made with α
d
igital delay unit .
frame. The events count, whic h is
d
is-
Th e measurement of t he d elay time be-
p
laye
d
on the crt rea
d
out, can be set to
With delay-by-events you have t h e
tween the transmitter p
ulses (Τ) an
d
any
n
umber from 1 to 10 million .
a
dd
e
d
conven ience of being able to
ec ho
p
ulses (R) of α ra
d
ar system ty
p
i-
select α
p
articular cloc k
p
ulse (t he 10th
c αΙΙγ calls for the measurement of long
The main reason for u si ng delay-by-
p
ulse, the 256t h pulse, etc. in α
long
is d is
p lay stability. Dis
p
lay sta-
ρ
)
g d
elay times wit h αη accuracy of α few
bί lity becomes α p
roblem with tr α
d
ίtί α-
pulse trai n to trigger the oscilloscope
nan osecon
d
s. Ιη this exam
p
le, the 7D11
οη . T h is relieves you of the j
ob of vis-
p
rovi
d
es α very accurate time refere nce
αΙ d elay-by-time measurements, when
υαΙΙγ counting cloc k
p
ulses οη th e crt
for this ty
p
e of measurement (see
F
ig .
the sign al
b
ei ng u se
d
to trigger the
d
is
p
lay.
20). Το ma ke this measurement, the
d elay is unstable . S
p
ee
d
variations in
α rotation
d
is k memory, for example,
transmitter
p
ulse is use
d
to trigger the
cause ty
p
ical
d
is k timing signals li k e
7D11 . The 7D11 delaye
d
trigger out
p
ut
origin or sector
p
u lses to j itter. Wh en
is t hen com
p
are
d
οη th e crt wit h t
he
using either analog or
d
igital time d
e-
ec ho
p
ulse . Coinci
d ence between the
Ιαγ, where the swee
p
is
d
elaye
d
by α
two
p
ulses is obtaine
d
by a
d
j usti ng the
fixe
d amount of time, this j itter causes
7D11 DEL AY ΤΙΜΕ OR EVEN TS an
d
the
d
is
p
lay to ju m
p
bac k απ
d
fort h.
F
or
F
I NE DEL AY controls . The d
elay time
h ig h time resolution measurements
d
is
p
laye
d
οη the CRT readout
p
lus the
,
setting of the
F
I NE DEL AY control is
the delay time between the transmitter
,- an
d
t
h e ec h o
p
ulses.