Agency: FBI
Originator: FBI
From: HQ
Document date: 02/15/1943
Document type: PAPER, TEXTUAL DOCUMENT

## Page 1

Released under the John F. Kennedy Assassination Records Collection Act of 1992 (44 USC 2107 Note).

DATE: 11-14-2017

JFK Assassination System

Date:

4/13/201

Identification Form

Agency Information

AGENCY :

RECORD NUMBER :

FBI

124-10366-10005

RECORD SERIES: HQ

AGENCY FILE NUMBER : NO FILE NUMBER

Document Information

ORIGINATOR: FBI

FROM: HQ

TO:

TITLE:

DATE: 02/15/1943

'PAGES:

159

SUBJECTS :

MANUAL OF INSTRUCTIONS

DOCUMENT TYPE: PAPER, TEXTUAL DOCUMENT

CLASSIFICATION: Unclassified

RESTRICTIONS: 1B

CURRENT STATUS : Redact

DATE OF LAST REVIEW: 12/07/1998

OPENING CRITERIA: INDEFINITE

COMMENTS: REVISION NUMBER 48

v9.1

DocId: 32318832 Page 1

---

## Page 2

Released under the John F. Kennedy Assassination Records Collection Act of 1992 (44 USC 2107 Note).

DATE: 11-14-2017

9A - B

SECTION 9, SOUND AND TECHNICAL EQUIPMENT

9A. LISTENING EQUIPMENT

During the course of certain investigations, it sometimes becomes

desirable to listen to conversations carried on by suspects or others

without disclosing to them the fact that they are overheard.

When such

conversations are carried on within a room or enclosure, it is poseible

•to make use of a concealed microphone, placed within.the room under

observation,.from which a pair of wires may be led to an amplifier and

associated sound reproducing equipment, located in a convenient hideout,

some distance away from the room under investigation. Two types of

amplifiers are supplied by the bureau for this, one known as the Detect-

aphone and the other as the Lafayette amplifier. Two models of Detect-

aphones are available, namely the older model PA-173 and the new PA-1e0

Briefcase Detectaphore.

9B., DETECTAPHONE

On each occasion requiring the use of the Detectaphone, a thorough check

should be made of the set before

its final installation is

made.

The

round drycells which serve as "A" batteries should read not less than 1

volt with the volume control completely on; new cells should read 1.5

volts and between 30 and 35 amperes.

The large "B" batteries should

read between 36 and 45 volts, although satisfactory operation may

occasionally be obtained with voltages as low as 30.

The small "C"

battery when new should test 3 volts and should be replaced when the

reading is less than 2.5 volts.

The "A" batteries will need the most

frequent replacing. After ascertaining that the batteries are in

satisfactory condition and that the tubes light up when the volume

control is turned on, the microphone should be connected to the amplifier

input terminals. The headphones are then connected to the output terminals

and the volume control advanced until the tubes light up and reception

is obtained.

In placing a microphone in a room to be occupied by a suspect,

there are several points which should be kept in mind in order to obtain

the most satisfactory operation. In the first place, concealment of the

microphone within a readily movable object such as a small table or chair

should be avoided, inasmuch as such concealment is very likely to result

in subsequent disclosure or breaking of the small wires leading from the

microphone.

Because the microphone can be affected only by the sound which

actually strikes it, a point of concealment should be chosen which is ex-

posed as much as possible to the open air of the room. For instance, a

cold air register would be a much more satisfactory place for concealment

than a desk drawer or bookcase.

In placing the wire leading from a microphone to an amplifier, care

should be taken that at all points

where connections are made, the

insulation has been thoroughly scraped from the wire and the bright metal

is exposed. It is absolutely essential that all connections be bright

and cléan, for otherwise, noisy operation or even failure to operate may

be expected; in addition, the two wires should not be permitted to touch

each other at any point where the insulation has been removed, as

such contact results in absolute lack of response from the microphone;

2/15/43

DocId:32318832 Page 2

---

## Page 3

Released under the John F. Kennedy Assassination Records Collection Act of 1992 (44 USC 2107 Hote).

DATE: 11-14-2017

9B

SOUND AND TECHNICAL EQUIPMENT

• the breaking of either wire at any point along the line has the same

effect, so far as microphone response is concerned, and therefore must

be avoided.

In connection with the size of the wire which may be used, it should be

guared unar nen using the carbon or dynamic type microphones the larger une

wire, the longer it may be made and still give satisfactory operation..

For

distances of 25 to 50 feet, very fine wire may be used without serious 108s

of response.

In general, however, the shortest line and the largest wire

consistent with satisfactory concealment and ease of handling should be used.

It should be emphasized that installation of a Detectaphone for actual

use should be started in sufficient time, prior to occupation of the

room, to allow the hook-up to be tested

and any necessary changes made or

defects in the set-up corrected.

The Field has been supplied with carbon microphones which are placed

in series with a battery for operation. An electric current flows through

the microphone and the latter serves as a variable unit to oppose this

current. depending upon the pressure applied to the carbon granules (or

§lobules! placed between two carbon lor metal! surfaces.

These two surfaces

act as the two contacts to which the two connecting wires are fastened.

In addition, one surface serves to hold the small carbon particles and is

fixed with respect to the case, while the other surface is the diaphragm which

vibrates and varies the pressure on the carbon particles according to the

sound waves impressed against it.

This vibration, and resultant change

in current opposition, causes the electric current to vary in direct ac-

cordance with the sound waves.

This weak electric current is amplified

of strengthened by the vacuum tubes in the amplifier proper.

If a carbon microphone is horizontal or more than 45° with the vertical,

the carbon particles do not make contact with the upper surface (diaphragm

or cup and no electric current will flow in the "broken" circuit. In

other words, the microphone will cease to function and no sounds can be

transmitted. If the small cover of

a carbon microphone is loosened or

removed the small carbon particles will fall out of their cup and be lost

entirely or spilled into the outside shell of the microphone. In either

case the material used to make the contact between the two sides of the

electric circuit is lost and the microphone is rendered more or less

inoperative, depending upon the amount of carbon particles spilled:

The Detectaphone unit includes one amplifier:

one small crystal

microphone with a grilled face

to plant in a room for sound pick-up; one

extremely sensitive crystal well microphone: to enable pick-up of con-

versations in adjacent, rooms; two

boosters for use with extension lines;

and one set of crystal headphones.

One booster may have a metal cap over the terminal posts; it must be

removed and then replaced when fastening leads to terminals. The connection

leads are of shielded wire, with the end of the shield wire serving as the

ground lead in all cases.

In connecting the headphones it' makes no

difference which wire connects to the ground terminal post. The knurled

bakelite knob on the amplifier box is the switch and volume control.

Turning the

knob to the right, in a clockwise direction, increases volume.

Be sure the

switch is off when amplifier is not in use

2

2/15/43

DocId: 32318832

Page 3

---

## Page 4

Released under the John F. Kennedy Assassination Records Collection Act of 1992 (44 USC 2107 Hotej.

DATE: 11-14-2017

SOUND AND TECHNICAL EQUIPMENT

9B - C

The best results with Western

Electric Dynamic microphones or sound

Power microphones will be obtained with shielded twisted pair wire,

but generally ordinary twisted pair wire will be satisfactory and more

easily disguised.

9C. BRIEFCASE DETECTAPHONE

The Briefcase Detectaphone

is a new improvement over the original

Detectaphone and is presently being obtained by the Bureau to meet the

need of new amplifiers for dictograph systems. It is a small compact

unit mounted in a briefcase for disguise and convenient portability.

The unit is about one-half the weight of the Detectaphone and has a higher

volume output. Batteries can be tested by switches and a self-contained

meter without removal from the amplifier case. All external connections

to the unit are made by using plugs fitting into extension jacks mounted

in the amplifier case.

All microphones capable of use with the Detectaphone can be used with

Three jacks are provided for using three

crystal microphones simultaneously and a single jack is provided for all

other types of Bureau microphones. However, an external battery is still

needed in series with a carbon microphone to provide power.

Special batteries are needed for the Briefcase Detectaphones and

care must be exercised in maintaining an adequate stock for emergency

use.

Ray-O-Vac P3A30, Eveready 733, Burgess W3OP1, or General V30AAA

may be used for the 45-volt batteries and General 2L1 may be used for

the lf-volt

batteries.

The Briefcase

Detectaphones recently received by the

Bureau bearing the name "Clarion" use one Eveready 742 battery for the lz-volt

"A" power and two Eveready Mini-max 455 for the 45-volt "B" batteries.

5

2/15/43

DocId: 32318832 Page 4

---

## Page 5

Released under the John F. Kennedy Assassination Records Collection Act of 1992 (44 USC 2107 Hote).

DATE: 11-14-2017

9D -E

SOUND AND TECHNICAL EQUIEMENT

9D. RADIO DECOY PACKAGE KITS

Eight complete decoy package kits are presently availaole for use

on extortion and similar cases.

The kit consists of a decoy package:

an auxiliary beat oscillator, antenna, spare tubes, batteries. and

operating instructions.

The decoy package itself is essentially a small, entirely self-contained

radio transmitter. The radio wave which it transmits is a continuous

unmodulated signal and therefore cannot be received on Bureau automobile

receivers or similar equipment without the use of the auxiliary oscillator

which is furnished

as part of the accompanying kit.

In operation, the properly wrapped decoy package is deposited according

to instructions. The car receiver: in conjunction with the beat oscillator,

picks up the signal which

is heard as a constant "beat" note or squeal

in the receiver.

The approach of a person or animal within 6 to 12 inches

of the decoy will result in a marked

change of pitch of the beat note and

contact with the decoy will cause the note to disappear completely.

The

disappeaance of signal indicates that the decoy nas been touched or

picked up.

Satisfactory operation of the decoy and oscillator unit over a radius

of approximately .4 to 6 mile nas been secured in practical operating

conditions using standard Bureau automobile receivers. Large buildings

and operation in congested downtown areas will necessairly decrease

the operating radius.

9E.

RADIO TRANSMITTERS AND RECEIVERS

The Bureau has available several types of radio transmitters for

investigative use.

The small briefcase transmitters; six of which

are available, are useful from the disguise standpoint and are capable

of transmitting over a radius of several blocks in downtown areas.

For greater coverage, a higher powered portable unit capable of

operation from 110-voit a.c. or 5-volt dic. sources is available. Two

high power transmitting stations disguised in trucks are also available,

giving a greater coverage and greater flexibility of operation. All of

the above-mentioned equipment is so designed as to be able to transmit

2/15/43

DocId: 32318832 Page 5

---