© Brooke Clarke, N6GCE

General Information

This is a survival radio that is carried in the emergency vest of air crew members. It can transmit a beacon (attention getting warble tone) on 243.0 MHz.  Voice on 243.0 or 282.8 MHz and Morse Code in Modulated Continuos Wave (MCW) mode on 243.0.  It will receive voice on 243.0 and 282.8 MHz.  The previous frequencies are for Military emergency communications.  The PRC-90 does not work on the civilian emergency frequency of 121.5 MHz nor does it work on the international distress frequency of 406.025 MHz.

Note: Aircraft radios use AM so that when two transmissions double both transmissions are heard.  This is unlike FM where if one station is stronger than the other (by about 3 dB) the capture effect eliminates the weaker signal and it is not heard.  Since an AM receive will not have an audible output when a pure CW signal is being received, a Modulated CW signal is used and the AM receiver outputs the modulation frequency.

          "The AN/PRC-90 radio set is a dual channel transmitter/receiver capable of transmitting up to 60 nm (line of sight,
depending on receiving aircraft's altitude).  It operates on guard (243.0) or SAR primary operating frequency (282.8) with
a mode for swept tone signal on 243.0 only.  Transmission of beacon or code can be up to 70 nm.  Average battery life is
about 14 hours.
            Radio is equipped with external earphone jacks to assist pilot in hearing radio transmission with helmet on."
from: FAM12


PRC-90-2 with 90BAv3
                    battery adaper
PRC-90-2 with 90BAv3 battery adapter
PRC-90-2 Mode Switch
PRC-90-2 Mode
The center of the mode switch needs to be pressed down to get to VOICE 282.2.
But you can just turn the drum for VOICE 243.0 & BCN 243.0.
When in OFF position Magnetic South near point of pointer/front panel
North pole near back.

The Antenna screws onto the radio with the 3/8 x 28 threads as ground and has a socket in the antenna as the hot connection.  The lower 6 1/2" of the antenna is flexible and when the telescoping sections are collapsed the overall length is 12" and extended it's 24" long.  The impedance looking back into the radio is 50 Ohms.  You can use the PRC-90 to BNC(f) adapter in the TS-24() test set to connect the radio to test equipment that's also 50 Ohms.

The earphone is in the black plastic pocket and is for use where enemy troops are nearby.

Maintenance Instructions

The TS-24B Test Set or the AN/PRM-32A (TS-20) can be used to test this radio.

The 9 screws that hold the back on the radio have a drop of olive drab paint/epoxy that covers the screws.

I have 2 of these from eBay both "working", but the 282.8 MHz function has weak audio on one of them.
Note: You can not do a valid test with old BA-1568/U batteries, you need proper voltage in order for the radio to work.

Inside after back cover is removed. - with labels showing modules and PCB removal screw.  When the PCB removal screw is out you can lift the PCB and modules part way out of the housing.  At this point you could trouble shoot and/or remove/replace modules if you had service documents.  If you have service documents let me know.


It uses a cylindrical battery that has a raised band that will allow the battery to only be inserted with the correct polarity (+ end first into radio).  The original battery was a 14.0 Volt Mercury BA-1568/U that has been replaced by the 10.5 Volt BA-5368/U LiMnO2 battery.
Note the BA-1568/U is rated for 1.0 AH and 14 Hours of PRC-90 operation per TM 55-1680-351-10 for the SRU-21/P Survival Vest.  The battery has a 3 year shelf life in temperate climates.

The pass Fail test for the BA-1568/U on the TS-183 Battery Tester was greater than 11.0 Volts with load 12 (21.0 Ohms).

The official and very expensive replacement is the BA-5368/U LiMnO2.  Mathews, Saft, Ultralife and Bren-Tronics make it. NSN 6135-01-435-7947

Label on Mercury Battery:

14.0 VOLTS


Label on BA1568/U Box:

6135 00 838 0706
DAAB07 87 D C036
A    9/88 MFD   9/88
        12                                                        11 VOLTS
Unless expressly authorized , this test information shall apply
to Army and Air Force applications only.


24 June 2002 - New 90BAv2 Battery Adapter has 1.3 AH capacity and can be used operationally.
There also may be a government official adapter that holds four each 123 photo batteries.

12 Jan 2009 - New 90BAv3 batteru adapter is same as 90BAv2 except has threads on bottom to hold radio cap.

The BT-70425 is a 12 Volt Lithium Manganese Dioxide Battery (LiMnO2), for use in the AN/PRC90 Radio set. The original battery for the AN/PRC90 Radio Set was a BA-1568/U Mercury battery. Due to various environmental issues, Mercury batteries have been mandated for elimination by the Environmental Protection Agency (EPA) wherever alternative battery systems exist. The BA-5368/U is a LiMnO2 battery that is a "form-fit-function" replacement.

Bren-Tronics’ BT-70425 is a direct replacement for both the BA-1568/U and the BA-5368/U. The BT-70425 incorporates a patented circuit with standard consumer cells to provide a safe and environmentally friendly replacement. Bren-Tronics developed this unique design feature, to allow a 6.0 Volt battery to operate like the 10.5 Volt battery required in the operation of the AN/PRC-90 radio set. The electronic circuit "steps up" the nominal six (6.0) Volts to the appropriate operating voltage, and maintains a consistent voltage similar to the original Mercury battery.

Testing the BT-70425 is also unique. Using a high impedance voltmeter, a minimum open circuit voltage (OCV) of 6.0 Volts DC will be measured.  To verify that the required 10.5 Volts is available, the electronic circuit must be activated. This is done by applying a load between 200 and 1,000 Ohms . After several seconds, the 10.5 Volts can be read on the same equipment as above. Once the operating or test load is removed, the circuit de-activates and the battery returns to a "sleep" mode, assuring the battery will provide its full and rated capacity. The BT-70425 is available for immediate shipment.

Audio Testing

There is no audio signal at the headphone terminals until the earphone connector is within about 1/8" of the radio so that the magnet on the connector will activate the switch in the radio.


PIN         TM/EM Number               Publication Title (partial)
 057428  TM 11-5820-800-13&P  RADIO SET, AN/PRC-90 (NSN 5820-00-782-5308)
 064945  TM 11-5820-1049-23P   RADIO SET AN/PRC-90-2 (NSN 5820-01-238-6603)
 067761  TM 11-5820-1049-12     RADIO SET AN/PRC-90-2 (NSN 5820-01-238-66


May be PRC-90 related, but probably prior beacons.

2866089 High-frequency radio transceiver, Maass Charles Frederick, Hoffman Electronics Corp, App: 1952-11-18, 455/73; 455/336 - improved vacuum tube frequency doubler to 243 MHz.

3299356 Pulsed carrier radio beacon transmitter, Kenneth F Bornhorst, Edward L Gliatti, William L Colello, NCR Corp, 1967-01-17 - optimizing the second harmonic generation to get 243 MHz.  The schematic shown is just for the transmitter and emergency beacon 300 to 1000 to 300.... modulation so not for a complete PRC-90.  This maybe for an earlier beacon transmitter?

3068415 Miniature radio beacon apparatus, Robert R Johnson,  1962-12-11- UHF 243 MHz output, 121.5 MHz crystal, prior art beacon weight 3.7# takes up 60 cu in and battery life was 20 hours.  Invention has 60 hours battery life and 1/3 the size and weight.  Pulsed tube filament to reduce power.  Tube acts as frequency doubler and power amp. Only one tube the rest transistors.
2555867 Air launched radio station, Robert P Bennett, 1951-06-05

Cited by:
Publication number Priority date Publication date Assignee Title
US3174103A *1962-09-061965-03-16Douglas Aircraft Co Inc Radio frequency beacon transmitter system
US3176229A *1961-11-091965-03-30Reginald R Pierce Radio rescue beacon
US3201695A *1962-10-011965-08-17Gen Motors Corp Am-fm all transistor radio receiver
US3207987A *1961-01-311965-09-21Kiryluk Wlodzimierz Radio rescue apparatus
US3265982A *1963-10-241966-08-09Hazeltine Research Inc Common emitter transistor amplifier including a heat sink
US3270284A *1964-01-131966-08-30William A Schanbacher Radio frequency signal transmitter arrangement
US3299356A *1964-04-101967-01-17Ncr Co Pulsed carrier radio beacon transmitter
US3303436A *1964-03-121967-02-07Krausz Robert Subminiature crystal oscillator of high stability
US3496471A *1966-01-251970-02-17Kel Kk Polarity reversal protection for transistor circuits
US4060764A *1976-03-251977-11-29Motorola, Inc. Transceiver audio system
US4101894A *1976-09-171978-07-18Warner Melvin B Cy Marshall Ii Radio beacon for a nautical emergency rescue system
US4112421A *1975-04-161978-09-05Information Identification Company, Inc. Method and apparatus for automatically monitoring objects
US4335375A *1978-02-131982-06-15Schaeffer Daniel D Container for an alarm transmitter adapted for insertion into a wall
US4376250A *1979-12-261983-03-08Dynamote Corporation Portable power source
Family To Family Citations
GB2237449B *1989-09-301994-03-30Hi Trak Systems Ltd Transmitter and antenna
2310017 Emergency transmitter, Hartman B Canon, Joseph L Swallow,  Wells-Gardner & Co, 1943-02-02 - use on land or water,
2497852 Transmitter buoy, Gilbert H Arenstein, 1950-02-21 - transmitter buoy & sea water activated battery
Publication number Priority date Publication date Assignee Title
US740317A *1903-01-251903-09-29Marine Torch Company Of Baltimore City Marine torch.
US1417692A *1920-11-131922-05-30Rosen David Battery
US1485776A *1920-01-031924-03-04John K M Harrison Marine signaling apparatus
US1503380A *1921-11-101924-07-29Samuel Rubinsky Battery construction
US2115744A *1936-03-241938-05-03William J Orland Illuminating device for swimmers
US2281284A *1937-05-201942-04-28Hammond Laurens Altitude determining means and method
US2293949A *1937-08-141942-08-25Pittsburgh Equitable Meter Co Altimeter
US2310017A *1941-05-051943-02-02Wells Gardner & Co Emergency transmitter
Cited by:
Publication numberPriority datePublication dateAssigneeTitle
US3497808A *1966-03-281970-02-24South Bay Associates Acceleration sensitive locating transmitter
US3569949A *1968-02-121971-03-09Roger Isaacs Wireless remote control system
US3617894A *1967-09-271971-11-02Marcel E Benoit Two-transmitter radio beacon
US3643162A *1969-07-071972-02-15Roger R Ady Transmitter producing in recurrent cycles time-spaced varied-power propagatable pulselike signals
US3723881A *1970-02-091973-03-27Drake Crandell & Batchelder Downed-aircraft radio-locator beacon and related apparatus
US3866177A *1972-08-121975-02-11Matsushita Electric Ind Co Ltd Remote control utilizing pulsed beam of light frequency
US4137500A *1976-12-071979-01-30Weber Harold J Frequency dependent amplitude modulated exciter apparatus
US4195268A *1978-02-271980-03-25Motorola, Inc. rystal oscillator including adjustable auto transformer for neutralizing crystal capacitance
US4335375A *1978-02-131982-06-15Schaeffer Daniel D Container for an alarm transmitter adapted for insertion into a wall
US4482867A *1981-10-231984-11-13Lmt-Radio Professionnelle Microwave power transmitter for doppler radar
US4528566A *1982-08-131985-07-09Tyler Michael D Transmitter and receiver locating device
US5226061A *1989-09-301993-07-06Hi-Trak Systems Limited Transmitters and transmitter circuits
US5515036A *1988-05-271996-05-07Lectron Products, Inc. Passive keyless entry system
US20070120602A1 *2005-11-152007-05-31Nec Electronics Corporation Variable gain power amplifier
Family To Family Citations
AU591095B2 *1985-02-181989-11-30Plessey Overseas Limited Improvements in or relating to radio transmitters

Test Sets

AN/PRM-32(A) (TS-20) - Two radios with antennas removed to check each other (good for pass, but if a failure then which radio is bad?)  Works with PRC-90 and PRC-106
TS-24B -  - single radio with antenna in shield box
BT-2B Battery Tester - for many survival batteries (TS-2530/UR and TS-2530A/UR were earlier versions)
TS-183 - Battery Tester

Other Radios in the Family

The PRC-106 is a derivative of the PRC-90-2 and provides both beacon and voice capability on the civil and military distress frequencies of 121.5 and 243.0 MHz. The PRC-103 and PRC-195 are other derivatives of the PRC-90.


The PRC-112() is the replacement radio.  It too uses a specialized battery instead of commonly available batteries, but there is an official battery adapter being developed by the government.  It's a shame it does not use the BA-5123 (CR123 photo battery).

This is the radio used in the movie Behind Enemy Lines.
The PRC-112 can send the yelp on the standard beacon frequencies of 121.5 & 234 Mhz or voice on those plus 282.8 MHz.  But it can be programmed to work on and frequency in the 225 to 299.975 Mhz range and if a signal comes in on that programmed frequency and the signal contains the 6 digit survivor ID number the PRC-112 will act as a transponder using the Distance Measuring Equipment (DME) protocol.  A SAR aircraft will then know the distance and using DF the bearing to the survivor.  The transponder also works on 243 and 282.8 Mhz (not 121.5 Mhz).

The switch positions are:
Full CCW = 121.5 BCN, 121.5 voice, 282.8 voice, Channel A, Channel B, 243 voice, 243 BCN.

The KY-913 is used to program the radio, set the variable frequency and set the ID code number.  The top of the KY-913 looks like the battery used on the radio and that's how they connect.  No cable in needed.

Oct 2006 - the current PRC-112 is the "G" version.  It includes a GPS receiver.

This is a completely different philosophy from the 406 MHz beacons that only talk to satellites which in turn talk to a central station far from the survivor.  The signals from a PRC-112 can be received by nearby troops but the 406 MHz signal can not.


AN/PRC-90 Legacy by Alan D. Tasker, WA1NYR

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[an error occurred while processing this directive] page created 12 May 2001.