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|  CHAPTER 1
THEORY
Section I. SYSTEM BLOCK DIAGRAM
1. Scope
antenna by a passive wave and applying the
following formula:
a. This manual covers field and depot
m a i n t e n a n c e for Radio Interference Meas-
Formula
uring Set AN/URM-85. It includes instruc-
tions appropriate to third, fourth, and fifth
Where:
f i e l d strength in microvolt
e c h e l o n s for troubleshooting, testing, and
p e r meter,
repairing the equipment, and for replacing
v o l t a g e induced across the
maintenance parts. It also lists tools,
a n t e n n a in microvolt,
m a t e r i a l s , and test equipment for fourth,
effective height of antenna in
a n d fifth echelon maintenance. There are
meters.
no maintenance functions allocated to third
Both the panel-mounted meter and the re-
e c h e l o n . Detailed functions of the equip-
mote multimeter of the test set have scales
m e n t are covered in the theory sections.
w h i c h are calibrated in microvolt (uv)
b. The complete technical manual for
(10 uv full scale) and in decibles (db) (20-db
this equipment includes TM 11-6625-351-
f u l l scale). A measurement is meaningful
1 2 , TM 11-6625-351-20P, and TM 11-
only after the meter has been calibrated by
6625-351-35P.
a p p l y i n g the output of the self-contained
c. Forward comments concerning this
i m p u r s e generator to the system.
m a n u a l to the Commanding Officer, U.S.
(1) T h e test set indicates the voltage
A r m y Signal Materiel Support Agency,
t h a t is present at the SIGNAL
ATTN: SIGMS-PA2d, Fort Monmouth, N.J.
INPUT connector of the main unit.
(2) The effective h e i g h t
of the
Note: For applicable forms and records, see par-
agraph 2, TM 11-6625-351-12.
antenna which is used for the
measurement is provided by refer-
d. Refer to DA Pamphlet 310-4 to de-
ence to graphs, supplied in the cali-
t e r m i n e what Changes to or revisions of
b r a t i o n book accompanying each
t h i s publication are current.
serial numbered m o d e 1 of the
equipment. Typical graphs showing
2. General Application
the antenna factor versus frequency
Radio Interference Measuring Set AN/
appear in TM 11-6625-351-12.
U R M - 8 5 is a portable test set which is
b. A second application of this test set
used in four different applications.
i s the use of the instrument as a tunable
a. One application is the measurement
two-terminal radiofrequency (rf) volt-
of the field intensity of radiated continuous
meter. In this application, the output signal
wave (cw), amplitude modulation (am.) or
f r o m such rf signal sources as a radio
f r e q u e n c y modulation (fm) signals. These
receiver, a tuned rf amplifier, a local
measurements are usually expressed in
o s c i l l a t o r , or a signal generator, is con-
m i c r o v o l t per meter (uv/m). The figure
d u c t i v e l y coupled to the SIGNAL INPUT
is obtained by dividing the potential differ-
connector of the main unit, without the use
ence between the receiving antenna system
and ground by the distance, in meters, be-
test set is 50 ohms in all positions of the
tween those two points. A more practicable
SIGNAL ATTENUATOR DB control, except
method to determine field strength consists
in the 0 SUBST. ONLY position.
of measuring the voltage induced across an
c. A third application of this test set is
2
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