7
The condenser which is built into the molded nose fs
-
lapge enough to insure accumte meter reading down to Sm-
quencies of 50 cycles or less. The Model 410k can, however,
he used to make measurements at lower frequencies. By re-
moving the plastic nose and usirig a coonfienser of .25 miwofarad
in series with the exposed contact of the probe, measurements
can be made with good accuracy down to 10 cycles per second or
less.
At; frequencies abave 100 megacycles, it 1s desirable
wherever possible, to use an external button-type conclenser
with the probe and to keep the distance between the point of
voltage measurement and the point of grounding the outside
cylinder of the probe as short as possible. This is particu-
larly desirable because Zn making measurements on typical
circuits operating at frequencies above 100 megacycles, con-
siderable voltage may be built up across ground leads or even
along various parts of a grounding plane. Coiisequextly, unless
the meter is placed as nearly as possible to She point at which
voltage is to be measured, erroneous readings may be obtaimd.
At higher frequencies, it is nearly mandatory %hat measure-
ments be made on voltages which are confined to transmission
Line circuits. For applications of tMs type the Hodel. 410A is
particularly suitable because the physIca1 confaguration of th-e
diode and probe is that of a concentr-fc transn3.ssfon 14nc and
with a few precautions It can be connected to typhal transmission
1Ine circuits with lit%!-e dfffli.cul.ty.
For measurements at the highsr frequencics, a special T-joint;
(-hp- Model 455A) can be supplled for connecting the >$ode1 41CU
directly across a 5O-o?m tt;ransnifssZor, line using Type N connect-
ors. This T-joint has been dcsigned so that the comect9on of
the Model 4lOA into a transmfssbon Y.be circuit wll.1 not cause
an apyreciable standing wave, With the aid of this d.evic:c,
measurement of power traveling through a transmission line my
be made with good accuracy to 1000 mc. The usual precautions
must 5e taken to provide accurate impedance matchfng a:id the
elimination of standing waves along the line through which power
is flowing. By using a dumy load z;t the receiving end of thfs
I!-joint, power output of various devices can be measwed. In
many applicatiors, potter going into a real load, such as an an-
tenna, can be conveniently measured up to frequencies as high as
1000 megacycles with good accuracy.
In other transmission line applications, it may be desirable
to connect the Model 410A into an existlng transmission Line.
This can be done by cutting the line away so that the center con-
ductor of the line is exposed through a hole large enough to clear
the body of the Model 410A probe. The nose of the probe shoulcl
be removed. A button-type capacitor of approximately'-?Qi> micro-
microfarads should be fastened to the center conductor of the t-.rc?ns-
mission line so that one terminal of the condenser contacts the
center conductor of the transmission 39ne and the other terminal
of the condenser contacts the anode connection of the probe. A
-7- |
ACEC
HEWLETT-PACKARD
