DZAAS Receiver

Drop Zone Assembly Aid System

Brooke Clarke 2007

DZAAS Rx operator's end


After a parachute drop someone on the ground needs to find the cargo.  This 28 channel receiver is designed to be worn on the left wrist and the LEDs help to find the beacon transmitter attached to the cargo.  There is a 10 yellow LED bar graph to indicate distance to the beacon transmitter.   This is a currently fielded system.  The top and bottom lids are sealed to the main body and so it's not designed to be repaired.  Uses surface mount technology.  This was one of the first military electronics units to make use of surface mount technology.  The parts so far all appear to be standard part numbers, not custom ICs.

This program was shelved when GPS went operational.  My unit has a 1983 contract number and serial No. 110.

I've heard that when the payload is dropped the aircraft that dropped it has a way to come up with Lat & Lon data that can be relayed to the ground crew who only need a common GPS receiver.

Receiver Operation

1.   Attach Antenna - Turn to Tighten.
2.   Attach Receiver to left wrist with antenna on outside of arm.
3.   Turn knob to assigned channel (1 to 28).
4.   Test battery by pushing toggle switch to BAT position.  If yellow light does not illuminate, replace battery (or connect antenna).
5.   Raise left are and turn until green (corner) light illuminates.  Walk in direction arm points.
6.   Yellow lights on end of receiver show relative position to assembly point.  TRN on indicates receiption of active transmitted signal.  Other lights move from left to right as you get closer.

DC Power

The 9 volt battery goes into a pouch that's part of the strap system that holds the receiver on the left wrist.


Antenna ConnectorPatent 5003316 (see below) clearly shows in Fig 6 that both loops and the sense antenna are inside the case so the connector has some other purpose.  Patent 4724442 (see below) mentions using rotating antennas which might be the purpose of the connector.  When an external antenna system is not being used there is some jumper in the mating cap.

The connector has one 0.070" dia pin (pin #1) and three 0.060" dia pins (pins # 2, 3 & 4).  It has a plastic body with exterior male threads.  I don't see any markings on it.  The outside diameter is about 0.692"  If If you know the model of the mating connector please let me know.

When a fresh 9 volt battery is connected and the toggle switch held in the "BAT" position the yellow LED does not light.  Normally this would indicate a bad battery or  missing antenna.  When the toggle is held in the "BAT" position and a screwdriver is used to randomly short pins in the antenna connector the yellow LED does light.

WorkingA small ball of aluminum foil wedged into the connector contacting pins 1 and 3 causes the BAT test to light the yellow LED next to the toggle switch.   Also the signal strength yellow LEDs near "FAR" are flickering but the yellow LED closest to "TRN" is off.  I think this is the proper condition at this stage.

The plot shown in the photo to the left was made with:
 the toggle switch =On
 Chan 21 (# next to LED)
 connector pins 1 & 3 shorted.
The 4395A spectrum analyzer shows new signals at:
164.6875 @ -77 dBm, 175.000 MHz @ -74 dBm, 185.3125 MHz @ -76 dBm and 195.625 MHz # -77 dBm.
Note that the adjacent gaps are all equal to 10.3125 MHz

Local Oscillator

The synthized LO seems to go from 176.720 MHz for channel 1 to 174.425 MHz for channel 28 so each step is 85 kHz.  Typically when the frequency goes down as the channel number goes up the LO is above the RF input by the IF.  Since the span of the LO is greater than the common 455 kHz IF the next most likley IF is 10.7 MHz.  So making a slight tweak to the LO frequencies moves them to:
Chan 1:  176.700  MHz LO - 10.7 IF = 166.000 MHz RF input
Chan 28: 174.405 MHz LO - 10.7 IF = 163.705 MHz RF input

Drawing of Folded
              Dipole on arm w/DZASS Rx
The antenna consists of both a loop and a sense antenna and these are contained inside the box.

You can see the 9 v battery pouch in the photo at the left and the cable going into the receiver.  The LED in the near corner is probably the Green To/From LED that's green when you are pointing To the payload.

Pins 1 (large dia) and 2 are connected toghther.  The yellow BAT test LED lights when pins 1 & 3, 2 & 3, 3 & 4 are shorted toghther.  But not 2 &4?  This may mean that there are two different antennas that can be used.  If you know please let me know.

Top Inside

DZAAS Rx Inside TopIn order to open the lid the four screws were removed and a dead blow rubber hammer used to crack the glue used to seal the lid to the box.  The bottom lid has not yet succumbed to the hammer so more blows are needed to get it off.

This photo shows the top lid removed and the digital PCB hinged out.  In the bulges beside the channel switch and the battery wire are two 5 turn coils oriented at right angles to each other and each has a variable trim cap.  These are the two orthogonal loop antennas.


The Class 342/4xx seems to be common to both of the E-systems patents for the DZAAS and as of 7 Jan 2007 there are 7810 patents in the linked search.

5003316 (.pdf) Single null miniature direction finder March 26, 1991, , E-Systems, Inc., 342/429 ; 342/419
A single null miniature direction finder which may be worn on the arm of the user and is fully automatic in operation. Signals from a single loop antenna and a sense antenna are summed; however, the amplitude of the sense signal is adjusted at first and second phase angles and the phase of the sense antenna is automatically switched from the first phase angle to the second phase angle prior to summing to produce either a single null or a no null pattern. These patterns are compared to each other as the user extends his arm horizontally and rotates his body. When the null occurs an indicator gives the relative direction to the transmitter.

4724442 (.pdf) Method and apparatus for loop direction finding with no ambiguity Feb 9, 1988, E-Systems, Inc. 342/434 - uses two loops and a sense whip antenna.  Replaced by 5003316 that uses only one loop and a whip sense antenna.  Includes 28 channel switch and LED indicator.
This patent mentions Contract DAAK20-83-C-0639 which is the contract number on the DZAAS label.  This patents olso shows a 28 position channel switch.

The below patents relate to direction finding

5706010 Method and apparatus for determining location of an unknown signal transmitter Jan 6, 1998, E-Systems, Inc.342/47 ; 342/13; 342/147; 342/193; 342/417 - The locator device transmits a pulsed signal that's close to the unknown transmitters frequency.  This causes intermodulation distortion to occur in the unknown transmitter.  By measuring the time from sending the pulse to the time when the 3rd order IM return signal arrives an estimate of the distance to the unknown transmitter is calculated.  The power level of the interrogating signal is not mentioned.

5502450 Single antenna direction-finding system March 26, 1996, E-Systems, Inc. 342/451 ; 701/300 - not DZAAS but instead intended for use on an aircraft.

5461387 Position and direction finding instrument Oct 24, 1995, Georgia Tech Research Corporation, 342/357.08

5394161 Path finder/tracker system Feb 28, 1995, John & Richard  Ubaldo, 343/702 ; 33/290; 343/894; 701/224

4876549 Discrete fourier transform direction finding apparatus Oct 24, 1989, E-Systems, Inc., 342/417 ; 342/194; 342/195

4489327 Direction finding  Dec 18, 1984, Racal, 342/432 ; 342/433

4410890 VHF Directional receiver  October 18, 1983, United States of America as represented by the FCC, 342/419 ; 343/767; 455/269; 455/351; D10/65 - VHF slot antenna and non conductive tube to earpiece for covert operation
4003060  Direction finding receiver Jan 11, 1977, United States of America as represented by the FCC, 342/419 ; 455/333; 455/351; D10/65 - CB radio by channel number
4263597  Nondisruptive ADF system April 21, 1981, United States of America as represented by the FCC, 342/434 ; 342/435; 342/436; 342/438 - does not disturb the modulation like doppler type DF sets
4121216 Direction finder antenna and system Oct 17, 1978, E-Systems, Inc., 342/424 ; 343/728 - uses crossed vert loops & sense antenna PLUT a horizontal loop to detect sky waves.


DIRECTION FINDER RECEIVER DZ-2 CRV-46152 28 VOLTS DC this is an RCA tube type aircraft receiver.  Not sure if it's also a Drop Zone type radio or general D.F. radio.

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