PRT-4 & PRR-9

©Brooke Clarke, N6GCE


Background

FM 7-7 calls this pair the PRC-88.  If either one is used by itself then the more common names apply.

Quote from book:
"As final testing of those prototype radios was about to begin in 1964..."
"Designated standard A in January 1966...Within months after the first 400 models arrived in South Vietnam in
March 1967, the Army discovered that those expectations were not met."
From: United States Army in Vietnam. Military communications, a test for technology. by Bergen, John D., GPO 1986
pages 256 and 450.

PRT-4A Transmitter

Is designed to hook on a belt and be hand held during operation.  The "A" variation adds a 150 Hz tone to be compatible with other VHF low band radios in the 47 to 57 MHz frequency range.
Front PRT-4 Scan
Overhauled 1991 - Label -
  • Lanyard - NSN 5985-00-933-2454
  • Slide -                                                                         NSN 5820-00-995-2261
  • AS-1999/PRT-4 Antenna -                                         NSN 5985-00-926-2589
  • CY-6115/PRT-4 Battery Case -                                 NSN 6130-00-908-9189

  • TM 11-5820-549-12 with changes 1 to 9

    Crystals

    Circuit showing crystals, Chan 2 on the left, Chan 1 to the right
    There are two, CH-1 and CH-2.
    They are marked CR-81/U  40.3 MHz corresponds to a Tx frequency of 51.0 MHz (Tx freq = Xtal Freq + 10.7 MHz)
    To access the crystals, back out the 4 captured screws on the back of the transmitter.
    HC-50U socket, .040 leads, 3rd overtone, +/- 10 PPM stability, series capacitor.  Cut the rock 10.7 Mhz below the operating frequency.

    Battery

    4BA battery Adapter

    Uses BA-399/U 15 Volt Battery, although there are 4 socket holes, only 2 are used.  Mine has a contract number DAAB07-83-D-H352 and was made by Bren-Tronics, Inc. Commack, NY, U.S.A. on their web page:  NSN 6135-00-926-0845 model: BT-70613
    The method of battery attachment is simpler than that used on the PRC-68 series.  It has the battery exposed to the elements but the PRC-68 series has the battery sealed from the elements.  You can see daylight through the side when there is no battery installed.  The bottom of the battery box is also open.
    The Tx draws about 180 mA from a battery with 14.8 Volts open circuit. (I question this now 28 Jan 2002)
     
    Volts
    I ma
    <7
    no output
    7
    48
    8
    58
    9
    78
    10
    84
    11
    87
    12
    88
    13
    93
    14
    96
    15
    95
    16
    95
    17
    97
    18
    97

    A NOS BA-399 measures 14.5 Volts open circuit and shows 25% of the green (75% depleted) on a PSM-13/U-314 test.

    Using 2 each fresh 9 Volt Energizer 522 batteries in series shows a voltage of 17.5 when the PRT-4 is keyed.

    Here are a couple of ideas for home brewed battery packs. PRT4.doc -> drawings to go with the instructions
    SGC Photo has the BA-399/U batteries, and sometimes the BA-505 for the receiver.

    Antenna

    The antenna is 6" long when collapsed and 25" long extended.  The male thread on the antenna is 0.433 across the points and is 28 TPI, maybe it's a 7/16-28? Photo of just the PRT-4 Antenna -

    PRR-9 Receiver

    This receiver is designed to mount onto a helmet and the helmet is required for proper grounding of the antenna.  If the radio is hand held it will not work as well as on a helmet.  It has a horn type speaker, or if an earphone is plugged into the "P" socket on the top only the earphone will output sound. On the bottom is an OFF-volume control and the earphone socket, covered with a spring loaded flap to keep stuff out of the hole.
    This is not the "A" version and will receive with or without the 150 Hz tone.  The PRR-9(XE-2) uses a couple of ICs instead of discrete parts and uses the 3 Volt  BA-4534/U instead of the BA-505/U.  The (XE-9) version adds squelch.
    Front PRR-9 Scan, Top PRR-9 Scan, Label Scan, inside of Loud Speaker - removed from receiver and new from Fair Radio

    AS-1998A/PRR-9 Antenna

    The antenna is 18" long.  It has a "tooth" that will fit into either of two slots on the receiver so that it can point up when holding the radio in the hand or pocket or point up when the radio is horizontal as when clipped to a helmet.  NSN 5985-00-926-2590

    Battery

    Opened BA-505 showing "N" cellsThe BA-505/U consists of 4 each "N" cells in series.  They are not welded to each other, but like in a flashlight there is a spring below the bottom negative terminal, in this case the spring is a piece of black foam rubber.  There is a metal strap running from the bottom negative terminal to the negative socket.  The outside case has no electrical function.  It may be possible to rebuild this battery by simply replacing the "N" cells.  You will need ot cut a slit into the cardboard tubes surrounding the batteries, or maybe there is a way to "lube" them so they can will slide out?

     It appears that conductive epoxy is used to make electrical connection between the "N" cell positive to negative joints (3 places).

    Uses BA-505/U 6 Volt battery that has 2 sockets, or BA-4534/U  Mine is marked:
    Battery, Non-Rechargeable, Dry
    BA-505/U
    NSN 6135-00-926-0844
    DAAB07-88-0-C026
    0889
    Delta Concepts, Inc
    Farmingdale, N.Y.

     Negative pin on radio is 0.092" dia and the  Positive pin is 0.125" dia.  Fair Radio says 5 Volts at 25 ma.  My BA-505 measures 6.3 Volts no load.
    My radio draws 21 mA with the volume control at max volume.

    Crystal

    Circuit showing the Xtal - You can see the screw that was loosened in the upper right. the brass pins in the upper right are the battery connector.
    The crystal is on the right just above the pull string.  The other crystal on the left is soldered in and is not the one to change freq.  The large tubular device in the lower center is a ceramic filter.  The metal "S" shape pointing down in the lower right corner is the contact for the antenna.

    The crystal is marked 40.300000 and corresponds to a Rx freq of 51.0 MHz. (Rx freq = Xtal Freq + 10.7 MHz)
    The crystal appears to be the same one as used in the transmitter.
    To access the crystal:
    Loosen the screw on the Loud Speaker side near the earphone jack a few turns
    Remove the two pan head screws, one near the center "F" in OFF and the other on the end opposite the earphone jack.
    You do not need to remove the Loud Speaker from the receiver box.


    Overhauled 1988 - Label, Packing List  in the box -

  • AS-1998A/PRR-9 New antenna -                              NSN 5985-00-926-2590
  • TM 11-5820-549-12 with changes 1 to 9
  • H-264/PRR-9 Head Set (ear phone) -                        NSN 5965-00-926-2591

  • TM 11-5820-549-50-1 (015798.pdf) Depot Maint. Man. for PRR-9(XE-2) has a functional description of the receiver with detailed descriptions of the various parts, parts values, pictorial & schematic diagrams, this Rx uses ICs instead of the discrete parts in the PRR-9 & 9A.
    TM 11-5820-549-12 has the instructions on how to disassemble the radios prior to using the IC-1189.
    RTM 11-5820-549-35 is a restricted document
    RTM 11-5820-549-24P is a restricted document
    PRT-4 & PRR-9 by Alan D. Tasker

    PRR-9 (XE-9)

    This was an experimental version that uses integrated circuits. The manual that's available is:
    TM 11-5820-549-50-1.pdf

    ID-1189/PR Indicator, Channel Alignment -         NSN 5820-00-930-9204

    ID-1189This is the piece of test equipment that's needed to recrystal the PRT-4 & PRR-9. It is powered by the same 15 Volt battery that is used by the PRT-4 transmitter.
    TM 11-6625-937-12 (013613.pdf) contains not only the operation instructions but also a little maintenance info
    TM 11-6625-937-40P (020010.pdf) has exploded drawings with parts ID info
    TM 11-6625-937-20P (033616.pdf) has limited exploded drawings and parts info
    TM 11-6625-937-12HR (041085.pdf) has a list of the items that go with the ID-1189


    References

    Fair Radio -
    Lee Frank -
    Mike Murphy -
    These are frequently on eBay
     
     

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