Wire intercom system for explosives detection


The 4040 miniature wire intercom system permits communication over any pair of wires.  The control box contains a microphone/amplifier assembly that has an output impedance of 2000 ohms.  Audio output is approximately 1/2 volt Peak to Peak (P/P). If a low impedance device (such as a blasting cap) is placed across the line, the output voltage is effectively shunted to zero, thereby preventing a mishap.  The special headsets supplied with the 4040 have an impedance of 2,000 ohms.  Standard 8 or 16 ohm headsets simply will not work.

The 4040 uses unique "Popper" clips that eliminate the necessity of removing the insulation from the wire.  Connect one 4040 to each end of the wire pair.  If the control box is clipped onto a pocket or belt, run the wire under the belt clip and loop it one turn to serve as a strain relief.  Insert the ear piece into the HEADSET-2K jack.  If the ear-hook is used, it may be adjusted for either ear.  If the stethoscope loop is used, it is worn with the grey tube under the chin and the sound output holes facing slightly forward about 30 degrees.

Place the SENSITIVITY (power) switch in the NORM position and communicate.  The switches are pull-to-throw type.

NOTE: If one way (simplex) communication is desired, the SENSITIVITY switch on the receiving unit may be left OFF.

The 4040's have sufficient sensitivity to pick up conversations within a 50 to 200 foot radius.  This feature may be used as follows: One 4040 is taken downrange and placed on the ground in the center of the work area.  The SENSITIVITY switch is placed in the HI position. The technician can then go about his/her work, giving comments and instructions to the command post in a normal level of voice.  The 4040 at the command post end will normally have its sensitivity selector in the OFF position.

To record the communications, prepare a 2 to 3 foot mini-plug to mini-plug (1/8 in.) cable.  Plug a mini-plug 'Y' adapter, available at most electronic supply stores, into the HEADSET 2K jack and plug the headset and mini-plug cables into the 'Y'.

Plug the mini-cable into the AUXILIARY (AUX) jack of the recorder and adjust for normal operation.  The AUX jack is an attenuated high impedance input jack.  If the recorder does NOT have an AUX jack, a 100K 1/4 watt resistor must be placed in series with the center conductor of the plug to plug cable (mentioned previously).  The resistor may be placed inside either of the plugs. Clearly mark the cable so it can be easily identified as an attenuating cable.

Normally a pair of 4040's are used to communicate, however, any number of 4040's may be placed on a wire.  The units are also sold individually for that purpose.

Make sure the power (SENSITIVITY) switch is in the OFF position when not in use.

As with any piece of electronic equipment, remove the batteries during periods of prolonged storage.

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