Type 7334-1 Loop Antenna has been
designed as a substitute for the AT-205/URM-6
antenna and is a replacement for Eaton Model
94607-1. It uses 36 turns of wire on a 5.25"
(13.3 cm) diameter form enclosed in an electrostatic
shield as described in paragraph 5.2.1 of
7334-1 is equipped with an epoxy-glass
base plate which serves as a spacer to enable the
user to place the loop at exactly 7 cm from the
face of the item under test as required by test
procedure RE01 of MIL-STD-462.
Connection to the loop is through a BNC connector which enables
coaxial cabling to the EMI receiver. The loop is supplied with a
correction factor graph showing the values in dB which must be added
to the reading of a 50 ohm EMI meter to obtain answers in either dB/μV/m
or dB/pT. The correction factor decreases as frequency increases
from 30 Hz up to approximately 15 KHz, where the factor levels off
and remains relatively constant up to 5 MHz.
The Type 7334-1 Loop Antenna is required by Test Method RE01 in
Parts 2 through 6 of MIL-STD-461C and RE101 of MIL-STD-461D.These
portions of the specification require magnetic field emission tests
of cables, equipments, systems and sub-systems installed in, or used
in, all phases of military vehicles, ships, submarines, aircraft
(including helicopters), spacecraft, or ground-based operations.
TEST METHODS RE01 and RE101
The Type 7334-1 Loop Antenna is positioned 7 cm from the face of the
equipment under test with the plane of the loop parallel to the
equipment face. The best position to begin with is opposite or near
a joint or seam.
The associated EMI meter is then scanned over the range 30 Hz to 100
KHz searching for emissions. At the frequencies where emissions are
found, the loop antenna is moved about the surface seeking the
strongest emission level.
When a strong signal is detected, the loop is oriented on its axis
for a maximum reading. This procedure is repeated for all surfaces
of the equipment under test. Although the specification is not clear
on the point, it appears to indicate that all six sides (including
the bottom) of an equipment must be tested in this manner.
When testing cables, the loop antenna is placed 7 cm from the cable
with the plane of the loop parallel to the cable. The non-metallic
base plate of the Type 7334-1 Loop Antenna provides a convenient
means for establishing the correct 7 cm distance.
Magnetic Field Loop Antenna
Type 7429-1 Magnetic Field Loop
RS01 Magnetic Field Tests
The loop antenna used for generating radiated magnetic fields is
fully described in Figure 1A of MIL-STD-461A. It consists of ten
turns of number 16 A.W.G. wire on an insulated form 4.72" (12 cm) in
diameter. The winding is placed on the form in a position which
allows the form to be used as a spacer to place the winding 5 cm
from the face of the item under test as required by test method
RS01 of MIL-STD-462.
The Type 7429-1 Loop Antenna has been designed to the exact
requirements of the specification. The loop winding is placed on a
durable plastic form and is equipped with banana jack style
terminals for connection to the test setup. The loop is not
In a practical RS01 test setup, the loop antenna is supplied with
the required current versus frequency by the Solar Model 6550-1
Power Sweep Generator. The current is measured with a voltmeter
connected across the Solar Type 7144-1.0 Precision Resistor which is
connected in series between the loop and the generator.
current in the Type 7429-1 Loop Antenna to generate the magnetic
field intensity required by test method RS01 at 5 cm from the loop
winding is depicted on a graph supplied with the loop. The required
current varies from a few microamperes to about 5 amperes as
frequency is adjusted over the range 30Hz to 50 KHz.
Magnetic Field Loop Antenna
Type 9130-1 Magnetic Field Loop
Receive or Generate Magnetic Fields
10KHz to 3 MHz
This antenna was designed as a replacement for Eaton 94608-1. It is
similar to Stoddart 91117-2, 30-inch diameter loop, supplied with
AN/URM-6B and NM-10A
EMI receivers. In addition to operating as a receiving antenna, the
Type 9130-1 Loop Antenna is capable of carrying ten amperes in test
setups for generating magnetic fields.
Although the antenna it is replacing is circular (30 inches in
diameter), the Type 9130-1 Loop Antenna is almost square, 28.5" x
29.75" with 6.31" radius at each corner (12.4 cm x 75.5 cm with 16
cm radius). This larger area results in an improved pickup factor.
The loop is wound with larger wire than the original, so that it can
carry more current in the transmitting mode. Fitted with Type N
As a receiving antenna the Type 9130-1 is more sensitive than the
original 30-inch diameter loops. The graph below shows the
comparison when connected to a receiver with 50 ohm input impedance.
When used to generate magnetic fields, the Type 9130-1 Loop Antenna
is capable of carrying up to ten amperes through its eleven turns,
making 110-ampere turns. With one ampere flowing through the
winding, the magnetic field generated is over 277.5 volts-per-meter
at one meter distance from the plane of the loop and 12.6
volts-per-meter at three meters distance. With ten amperes flowing,
the field intensity is 126 volts-per-meter at three meters distance
Test Method RS101 of MIL-STD-461D requires radiated magnetic fields
over the frequency range 30 Hz to 100 KHz to determine the
susceptibility or immunity of the equipment under test (EUT). Two
loop antennas are required for compliance with the requirements. The
radiating loop is 12 cm in diameter and the sensing loop (used for
calibration) is 4 cm in diameter. The Type 9230-1 Radiating Loop has
been designed so that the Type 9229-1 Loop Sensor can be attached at
the required 5 cm distance.
The test method requires calibration of the radiated energy at 1.0
KHz prior to the test. Calibration of the Type 9230-1 Radiating Loop
is accomplished by coupling the Type 9229-1 Loop Sensor to it at a
distance of 5 cm.
arrangement is indicated in Fig. 1 on the next page. With a known
current flowing in the radiating loop, the magnetic field can be
measured. Two graphs are supplied with the loops to make life easier
for the test engineer. Fig. 2 shows a typical correction factor
curve for the Type 9229-1 Loop Sensor. Fig. 3 indicates the amount
of current flowing through the Type 9230-1 Radiating Loop to
generate the required magnetic field, in dB/pT.
The current level to produce 110 dB/pT at 1.0 KHz is 3.0 mA. An
accurately calibrated EMI meter or spectrum analyzer will measure
this as 42 dB/μV. Adding the correction factor of 68 dB/pT/μV from
Fig. 2 equals 110 dB/pT as required by the specification.