AN-58 ANTENNA

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03330A000700010002-7
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 10
• Document Creation Date: December 27, 2016
• Document Release Date: May 29, 2014
• Sequence Number: 2
• Content Type: REPORT

Declassified in Part - Sanitized Copy Approved for Release 2014/05/29: CIA-RDP78-03330A000700010002-7
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AN-58 ANTENNA
A. INTRODUCTION
The AN-58 is a loop type antenna designed primarily for indoor use with
a transmitter with 5 to 10 watts of output power. It may also be used outside
but has no waterproofing and will not withstand rough handling. The antenna
may also be used as a receiving antenna when it is not being used for
transmitting.
B. DESCRIPTION
The AN-58 consists of a loop type antenna, a transmission line and a
tuning box, as shown in Figure 1. The transmission line has two Din connectors
for insertion into the transmitter ANTENNA and GROUND telminals. The tuning
box has a tuning knob and a neon bulb to indicate correct tuning adjustment.
C. NUMBER OF ANfhNNAS REQUIRED
1. Normally, one AN-58 and a 100-foot (30.4 metre) single-wire emergency
antenna will be supplied. A single AN-58 antenna will operate over a 2.4-to-
1 frequency ratio. The basic range of the AN-58 is 4 to 9 megacycles or 4,000
to 9,000 kilocycles. A 4-to-9 megacycle antenna will have 40 feet (12.2 metres)
of wire in its loop. Antennas with less wire have higher frequency ranges as
listed below:
Length of Loop Wire Frequency Range of the Antenna
(Feet) (Metres) (Megacycles)
35
10.7
4.5 to 10.2
30
9.16
5.0 to 11.3
25
7.63
5.5 to 13.2
20
6.1
6.0 to 16.0
2. When a single AN-58 will not cover the frequency range needed, two
are supplied. It is customary to adjust one to cover 4 to 9 megacycles and
the second one to cover 6 to 16 megacycles. Of these, the 4-to-9 megacycle
antenna has the larger amount of wire. Note that either of the two antennas
can be used between 6 to 9 megacycles as their ranges overlap. The overlap
makes it usually unnecessary to change antennas during a contact because of
transmitting frequency changes. However, if there is any choice, use the
larger antenna in the 6-to-9 megacycle range whenever possible because the
larger antenna is somewhat more efficient than the smaller one.
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D. CHOICE OF INDOOR OPERATING LOCATIONS
Good, fair and
following factors:
a.
poor indoor operating locations may be identified by the
GOOD - A frame (wooden) building.
- The top floor of a building.
- A room with windows facing the base
- A room with no large metal objects.
b. FAIR
station.
- A brick or stone building with no metal reinforcement.
- An intermediate floor of a building.
- A room with windows not facing the base station.
- A room with some metal objects but away from the antenna.
c. POOR - A building with metal reinforcement.
- The ground floor of a multi-story building.
- A room with no windows.
- A room with large metal objects near the antenna.
E. OPERATION IN GOOD INDOOR LOCATIONS
1. Often, it is easiest to erect the antenna horizontally, suspending
the loop on furniture as shown inFigure 2. The tuning box and the transmitter
should be located near each other on a table. The transmission line pin
connectors are inserted into the transmitter ANTENNA and GROUND terminals.
When the antenna is mounted horizontally, its radiation will be about the
same in all directions in ideal surroundings. However, almost every type of
building will affect the shape of the radiation of the antenna. There is more
power on the T-junction side of the antenna, and the radiation from the T-junction
side is least affected by surroundings. Therefore, the T-junction side of the
antenna should normally be located near the wall with windows, preferably
along a wall facing the base station.
2. It may be more convenient to erect the antenna vertically, suspending
the loop from the ceiling and walls of the room. Door knobs, door hinges,
picture frames, etc. may be used to support the loop. Adhesive tape, thumb
tacks (drawing pins) may be used to support the loop but they may leave
telltale marks. The T-junction side of the antenna should be located close
to a wall with windows facing the base station. The tuning box should be
located in a direction opposite from that of the base station.
3. The antenna may be laid out in the shape of a square, traingle or
a diamond as shown in Figure 3. All sides should be of equal length.
4. The antenna wires should be as straight as possible but need not be
pulled tight. They should be leid out in such a way that it is still possible
to walk in the room without stumbling over the antenna, thereby breaking the
antenna or damaging the transmitter.
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F. OPERATION IN FAIR AND POOR INDOOR LOCATIONS
1. Most buildings can be called FAIR or POOR operating locations. Most
buildings have some type of metal objects which have a major effect on the
performance of an indoor antenna. Even the electrical wiring in a wooden
building will have some effect. It is normal to encounter places in a room
where radio signals are cancelled (dead spots). There may be places in the
room where radio signals are not cancelled and may even be reinforced (hot
spots). It is extremely important to locate the T-junction side of the
antenna in a hot spot.
2. A hot spot can be located by using the AN-58 as a receiving antenna,
listening to the base station with a receive_ while moving the antenna about
the room until the strongest signal is heard.
3. First, erect the antenna either horizontally or vertically, as
recommended for GOOD indoor locations. Insert the antenna pin connectors
into the ANTENNA and GROUND terminals of the receiver and tune the receiver
to a frequency on which the base station can be heard. When the receiver is
properly tuned, slowly rotate the AN-58 tuning control until the base station
signal is loudest. Keep the volume control on the receiver down so that the
base station can just barely be heard in the earphones at all times when tuning
the receiver and the antenna. If the signal becomes louder when the antenna
is moved, turn the volume control down again until the signal is barely heard.
The human ear can detect small changes inkudness only when the sound in the
earphone is kept at a very low level.
4. Move the antenna about the room until the base station signal is the
strongest. The antenna must be kept in the shape of a square, triangle or
diamond. Each time the antenna is moved, the antenna tuning knob should be
readjusted for best reception. When the best location has been found, try
the antenna both vertically and horizontally in that location and choose
the position that provides the best reception.
5. If the base station cannot be heard at first, listen to any radio
station which can be heard on the receiver and find the best antenna location
for that station. This location will not necessarily be the best one, but it
may make it possible to hear the base station if the base station signal is
not strong. When the base station can be heard, the antenna must be moved
to the location of best reception for the signal from the base station.
6. Finding a "hot spot" in a room may be a difficult process but the
effort will result in better communications, or may make the difference
between communications or no communications in a particular room. Once the
best location for the antenna is found in a room, it is only necessary to
erect the antenna exactly the same way for each later contact from the same
room.
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G. USING THE AN-58 FOR INDOOR RECEPTION
1. When using the receiver to listen to base broadcasts, the AN-58 may
be used as a receiving antenna. When the transmitter is used, it is normal
to use the AN-58 with the transmitter and a separate antenna wire for the
receiver. Some transmitters have a provision for using the transmitting
antenna for both transmitting and receiving by means of a cable connecting
tae receiver to a connector on the transmitter or its power supply. In this
case, a separate receiving antenna may not be needed if the base station's
signal is normally strong. If the base signal is weak, this arrangement
may not be usable because the AN-58 would be tuned to the field transmitting
frequency not to the base transmitting frequency.
2. If base broadcasts are normally strong, a single-wire antenna should
be used with the receiver for convenience. When the base broadcasts are weak
or when there is high noise or other radio interference on the base frequency,
the AN-58 may provide improved reception. It is recommended that the AN-58 be
erected vertically for receiving, as it has some directional effects when it
is vertical. Interference may be reduced, and the base station signal may be
increased by rotating the antenna. To rotate the antenna, keep the T-junction
side of the antenna in one place and move the tuning-box side of the antenna
around the room, without changing the shape of the antenna.
H. OUTDOOR USE OF THE 4N-58
1. The AN-58 can be used out-of-doors with better results than from
inside a buildin,ca
2. The antenna should be erected as a vertical triangle as shown in
Figure, 4. The T-junction should be at the top corner of the triangJe, and
the tuning box should be at the bottom. The bottom side of the triangle
should. be kept at least one foot (30 cm) above ground for best results.
3. The T-junction may be supported from a nail driven into a tree about
12 feet (4 metres) above ground. String or wire can be tied to the tree to
support the antenna. A wooden or bamboo pole about 4 metres long will also
make a good support for the antenna.
4. When erected vertically, the antenna radiates best off the ends of
the loop. It has minimum radiation in a direction broadside to the loop.
Figure 5 shows the radiation pattern of the AN-58 as viewed from above the
antenna.
I. TUNING THE AN-58
Tuning instructions for the AN-58 accompany your transmitter instructions.
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I-ANTENNA WIRE
2-TRANSMISSION LINE
3-PIN CONNECTORS FOR
TRANSMITTER
4-TUNING BOX
FIGURE I
5-TUNING KNOB
6-NEON BULB TUNING
INDICATOR
7-"Tit JUNCTION
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1-TRANSMITTER
2-TRANSMISSION LINE
3-ANTENNA WIRE
4-TUNING BOX
FIGURE 2
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SQUARE
TRIANGLE
FIGURE 3
TRIANGLE
DIAMOND
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1
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1-TRANSMITTER
2-TUNING BOX
3-ROCK OR OTHER WEIGHT
4-ANTENNA WIRE
5-NAIL OR OTHER FASTENER
6-"T" JUNCTION
7-STRING
8-DIRECTION TOWARD BASE STATION
FIGURE 4
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I. VERTICAL AN-58 (TOP VIEW)
2. MAXIMUM RADIATION
3. MINIMUM RADIATION
4. DIRECTION OF BASE STATION
FIGURE 5
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