Much of the following operational and engineering information is from
analyzing how the radio works and does not appear in any of the manuals.
1.1 Equipment Description
1.1.1 Purpose of EquipmentThe U.S. Marine Corps accepted the "A" version in 1983.
Radio Set AN/PRC-68A (radio set) is a hand-held receiver-transmitter that provides ground-to-ground voice communications in the 30 megahertz (MHz) to 79.975 MHz band. The unit is capable of secure speech operation when it is used with the Secure Voice Module (SVM). The radio set can be used with a short or long antenna, with a standard military handset such as H-138/U, H-189/U or H-250/U, or with its built-in speaker-microphone.
This was the second in this series of radios. Instead of the eight modules used in the PRC-68, the "A" version uses two modules, one on the front side and the other on the back side.
The frequency synthesizer has a microcontroller that converts the Frequency switch positions into serial data for the synthesizer IC and generates the 150 Hz tone and battery saver waveforms. The "A" version adds a EEPROM so that the channel frequency assignments no longer need to be in a sequence.
There are now two new switches inside:
- Four filters for the frequency bands of:
- Band 1 = 30 - 39.975 MHz
- Band 2 = 40 - 53.975 MHz
- Band 3 = 50 - 63.975 MHz
- Band 4 = 60 - 79.975 MHz
The number of unusable frequencies for the PRC-68A is much lower than on the PRC-68.
- Four Antenna matching networks numbered the same as and covering the same frequencies as the above filters.
All the channel assignments must be in only one of the frequency bands. (On the PRC-68B and later radios these switch functions will be combined and the switch located on the front panel of the radio with the ANT label.
1.1.2 Characteristics, Capabilities and Features.The physical and electrical characteristics of the radio set are given in 1.3 Table of Specifications.
Special capabilities and features of the radio set are as follows:a. Preset Frequency Channel Capability - The radio set is able to be internally programmed with ten (10) preset frequency channels. The chanels must all be in one of the four filter/matching circuit bands listed above. Later model radios moved the ANT matching switch to the outside of the radio allowing any frequency on any channel.
b. Warning Tones - The PRC-68A generates a warning tone for low battery.
C. Antenna Matching Switch - The PRC-68A does not have an external ANT matching switch. The internal switch needs to be set for the frequency band in use. No Field Strength Meter (FSM) is needed when reprogramming the PRC-68A.
d. Liquid Crystal Display - The PRC-68A does not have an LCD.
e. COMSEC Operation - Provides 16 kb VINSON compatible secure voice operation by simple attachment of the KYV-2,-2A NSA approved COMSEC device between the radio set and battery.
The prior sentence is taken from the radio manuals, but the comments (see Links below) indicate that the radio is NOT capable of secure operation. This may be because of some problem with the KYV-2,-2A or maybe just some other reason like the KYV-2.-2A modules were not available in the needed quantity.
When the battery voltage goes down to 10 volts the speaker will sound a low battery warning. This may be heard by an enemy that is near by.
1.2 PhotosFront - Speaker Microphone and ID label
Front 1A3 Module - 814636-801 RF/IF with:
Back - Push To Talk
- Antenna Match switch - "0" = 50 Ohm position (for use in bench testing or with my 68AA Antenna Adapter and a 50 Ohm ant)
- R/T Filter switch - "0" = 50 Ohm position
- Squelch Adjust
Back 1A2 Module - 814635-801 Synth/AF with:
Top,- there are just 5 terminals on the audio connector, matching the H-250 handset (6 terminals on later models) pin E on the AUDIO connector is for vehicle power.
- A (3,4,5,6 or 7), B (0 through 9) [C is the exterior CHAN switch] and D (0, 2, 5 or 7) Frequency Programming switches
- LOAD, NORM Programming switch The "D" frequency steps really are 00, 25, 50, 75 kHz.
- Low Battery Tone threshold adjustment (can be set at zero = no tone).
Figure2-3 showing A, B and D frequency programming switches, LOAD-NORM switch and Low Battery Adjustment.
When using pin E for power the radio operates with the switch set to OFF! This is the way they decided to save the batteries.
The antenna connector has a 5/16" x 24 threaded hole.
If someone hands you a PRC-68A radio there is no way, of determining what frequencies is has been programmed for. On all the later radios there is an LCD that displays the Rx and Tx frequency as the band switch is changed. The internal switches are only active while programming a single channel and can be changed so that even the last channel programmed may not be given away by the switch positions. All that you can tell is which of the four frequency bands is in use.
On the PRC-68 you can tell all of the channels by looking at the programming switches. On all the later models you can see the frequency in the LCD, but on this radio you need a spectrum analyzer or scanner to find out the programming. Maybe this was the major reason for the PRC-68B?
Bottom - battery snap connectors and SVM plug.
1.3 Table of Specifications
Frequency Range 30.000 MHz - 79.975 MHz Available Channels 2000 in 25 kHz increments Minimum Channel Spacing 25 kHz Preset Channels 10 in one filter band Modulation Frequency Modulation (FM) Operating Temperature Range -40 deg F to +159 deg F (-40 C to +65 C) Weight (battery, antenna included) 50 oz (1.42 kg) Size 9.35" (237.5 mm) x 3.8" (96.52 mm) x 1.52" (38.61 mm) Communications range - long antenna & goose neck 1.0 mile (1.6 km) Communications range - short (rubber duck) antenna 330 Yards (300 meters) Typical power consumption 25 mA when in receive mode with the radio quiet (0.8 AH for NiCad batt / .025 = 32 hours of Rx only time) 40 mA when VOL is set at max and radio driving internal speaker (20 hrs of listen only time) 270 mA when transmitting (3 hrs of Tx only time)
Power Output 1 Watt Frequency Control Built-in Synthesizer Frequency Stability 0.005 percent Spurious and harmonics radiation 50 dB below RF carrier level Modulation Limiting +/- 15 kHz Dev max 148 to 152 Hz Squelch Tone 2.5 to 3.5 kHz deviation
Adjacent Channel Rejection -60 dB Image Rejection -40 dB Sensitivity 0.5 microvolts for 10 dB SINAD Squelch sensitivity 0.5 microvolts Selectivity, 6 dB down bandwidth greater than +/- 15 kHz , 60 dB down bandwidth less than +/- 50 kHz Response to Spurious Signals -60 dB Audio Output less than 10 % distortion at 20 milliwatts
SINAD = (Signal + Noise + Distortion) / (Noise + Distortion) Squelch although 150 Hz is sent during transmission
the receive squelch operates based on signal not 150 Hz tone.
3.1 IntroductionBecause of it's size the PRC-68 will not fit into a shirt or pants pocket (maybe a battle fatigue pants pocket). Your choices are hold it in your hand all the time, OK for some uses, or use the carry bag connected to a military pistol belt and use the H-250 handset, or in quiet locations where you can hear the built in speaker, the M-80 Microphone.
3.2 Controls, Indicators and ConnectorsEach operating control, indicator and connector on the radio set is identified in the photos above and described in paragraph 3.4.
3-3 Frequencies with Reduced SensitivityThe following frequencies have receiver sensitivity reduction (the squelch may not quiet).
If they are selected during testing in Section 5, erroneous readings may result.
If they are used in the field the reception range will be greatly reduced.
BOLD frequencies are unusable.
32.000 44.800 50.000 62.5000 32.675 48.000 51.200 64.000 32.700 48.025 56.650 65.300 32.725 48.050 56.675 65.400 32.750 48.075 56.700 70.400 32.800 50.000 56.725 72.000 37.500 51.200 56.750 72.025 38.400 56.775 72.050 56.800 72.070 57.600 76.800 62.500
3.4 Description of Radio Set Controls, Indicators and Connectors
Name Photo Description ANT connector Top Connects antenna (or 50 Ohm cable using 914598-801 adapter.) . CHAN selector switch Top Selects one of 10 preset operating channels. OFF/ON/SQUELCH DIS switch Top Turns radio set on (clockwise) or off (full counterclockwise).
The spring loaded SQUELCH DIS position will disable the squelch as long as it is held.
VOL Top Controls the audio volume AUDIO connector Top Standard U-228/U style 5 pin connector for use with external handset, or SVM key fill divice PUSH TO TALK switch Back Enables radio set to transmit when pressed in normal operational mode. Battery Connectors Bottom Connects battery to radio set. SVM connector & Plug Bottom Provides interconnection between SVM and radio set.
Jumper Plug allows radio to operate when SVM is not installed.
Speaker/Microphone Front Functions as a built-in speaker (receiver) and microphone (transmit) when external handset is not connected.
When an external handset or headset is connected the internal speaker will go into mute mode.
3.5 Antenna ConnectionThe threaded hole that the antenna mates with has a 5/16" X 24 thread the same as the PRC-68, PRC-126, PRC-128 but different from the PRC-68B that has a 1/4" X 28 thread.
3.5.1 Short AntennaThe Short Big Base Rubber Ducky antenna is used for communications to 300 meters.
3.5.2 Long AntennaJust the tape measure antenna is used for communications out to 1,600 meters.
3.5.3 50 Ohm AntennaWhen an external 50 Ohm antenna is used the Antenna adapter is used to convert from the special radio connection to a standard BNC(f) connector. The internal Filter and Antenna Matching switches need to be set to the "0" position for 50 Ohm operation. My 68AA Antenna Adapter has a built in DC return.
The OE-254 and the RC-292 should work with this radio.
The OF-185 PS/A needs to be tested with the PRC-68 and PRC-68A.
The Diplexer, VHF, CU-2194/URC needs to be tested.
3.6 DC Power
The PRC-68A uses external power when the OFF-VOL control is turned OFF.
3.7 HandsetThe H-250 Handset can be connected to the AUDIO connector. This allows the Squad Radio to be carried in it's Carrying Bag attached to a standard pistol belt.
There is a flat on the handset connector. If this flat is positioned on and parallel with the PUSH TO TALK side of the radio it will mate with a small amount of rotation saving some time. This can be easily done by feel.
Other U-229 Audio accessories should also work with this radio such as the H-138/U, H-189/U handsets.
3.9 Manual Channel Frequency Programming
If you are handed a PRC-68A radio, there is no way to determine what frequencies have been assigned to each channel without using another radio or test equipment. This may be the major drawback of the PRC-68A.
NoteBecause of the 25 kHz channel spacing it may not be possible to program this radio to some pre assigned frequency that does not fall on the 25 kHz steps. Like ham band repeaters.
There are 4 switches used to control the frequency of operation of the PRC-68A called A, B, C and D.
NoteDuring the frequency programming process the CHAN control is used in two very different ways:
- While in the NORM mode the CHAN knob sets the channel frequency 0.1 MHz digit
- When in the PROG mode the CHAN knob determines the channel to be programmed.
The C switch is the 10 position CHAN switch on the top of the radio. The A, B and D switches are located on the Synthesizer module. These switches are labeled directly in frequency and do not follow the PRC-68 definitions.
Figure2-3 showing A, B and D frequency programming switches, LOAD-NORM switch and Low Battery Adjustment.
To setup a channel:
1 - Turn off the PWR OFF/ON/SQUELCH DIS switch
2 - Remove the battery
3 - Remove the module housing by unscrewing the two captive screws on it's bottom
4 - Reconnect the battery. (This is easier if the radio is laying on a flat surface with the (back) Synth/AF module facing up).
5 - Determine which of the 4 frequency ranges will be used for the current channel programming and set the R/T FILTER and ANT MATCH switches to the corresponding band number. (some do this after programming to maximize field strength, but I have not yet worked on this.)
Band 1 = 30 - 39.975 MHz6 - For each channel to be reprogrammed:
Band 2 = 40 - 53.975 MHz
Band 3 = 50 - 63.975 MHz
Band 4 = 60 - 79.975 MHz
- Confirm that the PROGRAM switch is in the NORM position
- Turn ON the PWR switch
- Use the small screwdriver that is held under the module housing to set the "A", "B" and "D" switches to the desired channel frequency. Use the CHAN control to set the "C" frequency. Example: 51.00 MHz A=5, B=1, C=0, D=0
- Set the PROGRAM switch to LOAD
- Set the CHAN selector to the channel to be programmed (I have better luck by rotating the CHAN switch to zero and back to the channel number to be programed)
- Set the PROGRAM switch to NORM (when the switch is moved to the NORM position the channel is programmed into the EEPROM.)
After the channels are reprogramed and the FILTER and ANT MATCH switches have been set, the radio is ready to use
When using the 68AA Antenna Adapter with an antenna that's nominally 50 Ohms or when using it to make a direct connection to a test set like the TS-3354 or PRM-34 you need to configure the radio for 50 Ohm operation.
Set the Antenna Match switch on the RF/IF module (1A3) to 0. This disables the antenna matching.
Squelch AdjustmentFigure 2-2 showing the ANT MATCH, R/T FILTER switches and the SQ ADJ pot.
If the Band was not changed proceed to step 3 below.
If the Band was changed the squelch should be readjusted by
1- Turn SQ ADJ counterclockwise until noise is heard in the SPKR/MIC
2 - Turn SQ ADJ clockwise until the radio is quiet and turn 1/2 turn more
3 - Turn PWR to OFF
4 - Replace small screwdriver in cavity on bottom of module housing
5 - Install module housing onto radio by tighting the two captive screws.
Difficult to Get CorrectIt is difficult to get the desired frequency. While trying to program 51.0 MHz on Band 3 I got slightly high result.
Even when using Band 2 for 51.0 MHz, it took a number of tries to get it correct.
The last time I rotated the CHAN switch on the top of the radio to CHAN 0 and back to CHAN 5 then switched to NORM.
Without another radio or a spectrum analyzer it would be very difficult to set up this radio.
Maybe mine is different from the rest, but I don't think so.
10 Jan 2002 - it may be that I did not fully realize the significance of the two modes of the CHAN control.
Confirming that all the crystals are OK by using the 914598-801 adapter going to the Agilent 4395A spectrum analyzer you can see:
24.999999813 MHz @ -116 dBm = 2 * 12.5 MHz mixer crystal
12.800159702 MHz @ -121 dBm = 2 * 6.4 MHz synthizer crystal
76.58 kHz @ -139 DbM = Microcontroller crystal
3.10 Manual Split Tx & Rx Frequency Channel ReprogrammingThe PRC-68A does not support split Tx and Rx operation.
3.11 Reading (up loading) Channel DataThe PRC-68A does not support data transfer.
3.12 Filling (down loading) Channel DataThe PRC-68A does not support data transfer.
3.13 Repeater OperationThe PRC-68A does not support repeater or retrnasmission operation in the conventional military sense, but the Radio Shack 19-345 time offset repeater does work. When using the Radio Shack 19-345 and powering both the radio and repeater unit from a wall wart the current capacity needs to be at least 300 mA.
3.15 Carry BagBecause of it's size the Squad Radio will not fit into a shirt or pants pocket (maybe a battle fatigue pants pocket). Your choices are hold it in your hand all the time, OK for some uses, or use the carry bag connected to a military pistol belt and use the H-250 handset. There are pockets for: radio, antenna, battery and a holder for a handset.
Front Photo - showing a Squad Radio in the main pouch with H-250 attached and a spare battery in the front pouch. There is a place on one side to hold both antennas and on the other side a velcro flap to hold the Handset.
Back Photo - has two standard military pistol belt clips and will not attach to a standard civilian belt. The bottom of the main pouch has an insert so that when removed will allow for the extra length of the Secure Voice Module.
It may be the case that the original Operator's manual would also fit into the main pouch with the radio, but that's just a guess based on the possible manual size. The reprint manuals are 8.5" x 11" because that's the standard copier paper size.
3.16 150 Hz Tone DisableThe PRC-68A does not support disabling the 150 Hz tone during transmitt. When testing a seperate 150 Hz filter needs to be used.
3.17 SPKR/MIC Mute CircuitThis is the circuit that puts a DC voltage on the handset speaker in order to determine if there is an external handset. If it finds that the resistance of the handset is below some value, then it mutes the internal speaker.
3.18 Frequency PlanningWhen deciding on which frequencies to use in the range of a Squad Radio consideration should be given to a number of factors.
You may want someone to hear your transmission that has only a commercial receiver.
You may not want someone with a commercial receiver to eavesdrop on your transmissions.
- frequency allocations for the locality where the radio will be operated (some are on my freq allocation web page)
- avoid using frequencies were the radio may have spurious responses
- In areas where there are TV stations you may want to avoid using the frequency band for active channels. TV uses the same 100 kHz FM modulation as FM broadcast radio so if you tune to the audio carrier the signal will not be clear, but speech is understandable. By the same token you can transmit to a TV receiver tuned to one of these channels, and although not clear speech is understandable.
- TV 2 = 54 to 60 MHz, Video carrier = 55.25, Audio carrier = 59.75
- TV 3 = 60 to 66 MHz, Video carrier = 61.25, Audio carrier = 65.75
- TV 4 = 66 to 72 MHz, Video carrier = 67.25, Audio carrier = 71.75
- 72 to 76 MHz is not a TV allocation
- TV 5 = 76 to 82 MHz, Video carrier = 77.25, Audio carrier = 81.75
Another factor is the use of loop antennas for Direction Finding. The popular US models AT-339/PRC (38 - 55.4 MHz) and AT-748/PRC (30 to 76 MHz) range and do not completly cover 30 to 79.95 MHz. This may be a reason to use or not use the 76 to 88 MHz range.
- Many hobby scanner radios cover 29 to 54 MHz but not 54 to 88 MHz because of the above TV allocations.
3.19 Antenna PlanningWhen these radios are going to be used for an operation, some thought should be given to the antennas for each radio whether used as a base, mobil, or repeater/retransmission radio. There is a tradeoff. using the ducky results in short range which may be a good thing depending on the circumstances.
If you are looking for the maximum range, without going to amplifiers, then the best antennas and siting will be needed.
3.20 SpeakersIt is possible to use the military speakers like the LS-454 with the Squad Radios, but it would be awkward to transmit by using the radio's built in microphone. The amplified speakers AM-4979/GR and AM-6747/V have vehicle DC power inputs and a pass through connector setup that allows connecting either a handset like the H-250 or more practical a microphone like the M-80. The AM-4979/GR is specified for +28 VDC operation, but inside there is a 1N2976 12 Volt Zener diode, so it looks like it would work just fine on a 13.6 VDC standard car supply. A wire may need to be added from the 13.6 supply to pin E on the squad radio AUDIO connector to allow the radio to run off of car power.
3.21 Sub Audible (CTCSS) ToneThe PRC-68A transmits a 150 Hz tone so that it can talk with older radios like the PRC-25, PRC-77 and AN/VRC-xx radios that need to hear the 150 Hz tone to open their squelch. This tone is not used by ham radio operators for repeaters, so the PRC-68A can not operate on any repeater that needs a specified sub audible tone. Also see Squelch Capture.
There are aftermarket CTCSS tone generators that may be adapted for this use. More needs to be done.
4.1 8 ModulesThe PRC-68A and all the later Squad Radios use two modules. On the front side there is the 1A3 RF/IF module and on the back the 1A2 Synth/AF module that also contains the microcontroller.
The way the modules on the PRC-68A work is different from the newer radios. It uses a 12.0 MHz deviation oscillator out of the Synth module on pin P2-10 for transmit and the later radios use a 21.4 MHz deviation oscillator out of the Synth module on pin P2-2. This means that the PRC-68A modules can not be used on any of the newer radios.
TSEC/KYV-2A Secure Voice Module SVM
This optional unit is issued to authorized users and is installed between the bottom of the radio and the battery. It has two captive screws that hold it to the bottom of the radio and it has battery latches like are on the bottom of the radio for attaching the battery.
The SVM is compatible with the VINSON comsec system used on a number of military radios and the KY-57 and KY-58.
The 16 kb/sec digital data is compatible with MIL-STD-188-220 the Estelle data link protocol. (There is another secure voice encription system that uses a 12 kHz data stream.)
The 15 pin mating connector has the following terminals:
In the jumper plug used when the SVM is not installed, (14 - Tx audio) is jumpered to (1 - Tx Cipher) and (5 - Rx Cipher) is jumpered to (4 - Rx audio). The Rx audio has a low pass filter to reduce the noise that comes with non secure audio in a wide bandwidth.
- 1 - Tx Cipher (12 kHz) to modulator (digital data interface?)
- 2 - Gnd
- 3 - Chopped B+ (generated by the battery saver circuitry)
- 4 - Rx audio (3 kHz) to speaker or handset
- 5 - Rx Cipher from receiver (12 kHz) (digital data interface?)
- 6 - Rx B+
- 7 - Squelch Disable
- 8 - TTL digital coms with micro controler, probably for key loading (block diagram has no label )
- 9 - 150 Hz Disable (150 Hz is disabled for secure coms)
- 10 - Gnd
- 11 - On/Off Run B+
- 12 - Tx B+
- 13 - Gnd
- 14 - Tx audio from microphone ( 3 kHz)
- 15 - Battery B+
PCG-68 - Programmable Code Generator is used to load the . . .
CSD-68 fill gun (Code Source Device?) that in turn puts the key into the . .
TSEC/KYV-2A Secure Voice Module (SVM).
The SVM attaches to the bottom of the Squad Radio with two screws and the battery latches onto the bottom of the SVM using the same latches on the battery as are normally used for the radio.
MicrocontrollerThe brains of the radio is a microcontroller in the Synthesizer/AF module There is no LCD display on the PRC-68A. It's probable that the microcontroler uses 8 bit words sinse that would be approiate for the time frame when the radio was developed. The PRC-128 uses the Motorola XC68HC805C4P so it's likley the same basic chip is in all the radios from the PRC-68 onward. There is a EEPROM in the PRC-68A and this is how the random channel adssignments are stored.
The information below is based on the PRC-128 and may not be correct for the PRC-68A.
- U1 - LM3361AN which is an IF amplifier, squelch circuit, FM detector, it takes in 455 kHz and outputs Audio & ? kHz crystal
IC MASTER Online - to lookup the above part numbers from the PRC-128 Depot manual (don't have a Depot manual for the PRC-126).
- U6 - 40 Pin Microcontroller (Motorola XC68HC805C4P) & 76.8 kHz clock crystal
- U5 - NMC9346C EEPROM 64 words each 16 bits long - manual only talks about 20 words of freq data, is the rest used for something else?
- U7 - Allegro UCN-5895A serial in - 8 parallel bits out power switching up to 250 mA per pin
- U3 - MC145156L PLL Synthizer & 1.6 MHz crystal
- U8, U9 - LM158 op amps
- U2 - MC33174AP op amp
For repair advice you can contact Jim Karlow, KA8TUR He might do a repair, but it is the third priority for him after his job and family.
TS-3354The TS-3354 was designed for testing the PRC-68 but can be used with other Squad Radios in this family.
TS-3951/PRM-34This is a more modern version of the TS-3354 for use with newer 30 to 88 MHz squad radios.
This test set contains a frequency counter, power meter for forward and reverse and a comb generator to test receiver squelch as well as a field strength meter so that the PRC-68 antenna circuits can be adjusted.
PS magazine - ???
Audio/Power Test AdapterThis has the following parts:
The above circuit diagram is from TO 31R2-4_810-3 for the PRC-128.
- Red and Black clip leads for connection to a power supply that can provide less than 10 to 15 VDC at 0.5 Amp
- U-183 connector on a cord to mate to AUDIO connector J5 on PRC-126
- Momen - OFF - ON switch for the PTT function
- SPKR/MIC switch to select INT or EXT
- BNC(f) connector for receiver audio output
- BNC(f) connector for DE-MOD?
The 914877-801 is an earlier version of the Audio/Power Test Adapter and is a part of the MK ()/PRC-68 Maintenance Kit.
Tool Kit TK-101/GManual SC 5180-91-CL-R13
Contains the spanner wrench for the antenna connector.
Description NSN Figure Item FSCM Part No. Radio Set PRC-68A 5820-01-180-8943
37695 705956-804 Receiver Transmitter
5820-01-229-6812 Fig 1 4 80058 na Carrying pouch 8465-01-152-1157 37695 349924-1 Carrying Harness Sling 37695 348814-2 Lanyard 5985-00-933-2454 Fig 1 2 80063 SM-B-522304 Short Antenna 5985-01-096-9396 Fig 1 1 37695 914161-803 Alignment Tool 5820-01-096-9410 37695 808234-1 36" Long tape meas Antenna AS-3575/PRC
5820-00-889-3803 Fig 1 4 37695 Battery Spacer Fig 1 3 37695 347344-1 ID Plate Fig 1 5 155035 1A1 Frame & Panel assy 5820-01-094-6523 Fig 2 1 37695 917327-803 1A2 - Synth/AF module
37695 814635-801 1A3 - RF/IF module Fig 2 3 37695 814636-801 1A?10 module cover Fig 2 7 37695 918267-803 1A?11 Battery Housing
Fig 2 9 37695 914153-803 Antenna Connector Adapter with BNC(f) 37695 914598-801 Handset 5965-00-043-3463 80058 H-250/U BA-5588/U Battery Dry Lithium/SO2
replaced by BB-388
80058 BA-5588/U BA-1588/U Battery, Mercury 6135-01-088-2708 BB-588/U Battery, NiCad including housing 6140-01-091-1536
Simple battery Charger Single Station Battery Charger 37695 565604-801 Five Station Battery Charger 37695 706841-801 Bren-Tronics model BB-388A/U 6140-01-419-8190 AP-388/U Battery to Charger adapter (holds 2 batt) 5940-01-427-8601 BA-715 for only the PRC-68,-68A & 68B? PP-8444/U, Universal Portable Charger (UPC) costs $562.52 new
TM 11-6130-489-13&P (075017.pdf) is Restricted on ETM
6130-01-427-9110 Silicon Compound, 2 oz 6850-00-177-5094 Lint Free Cloth, yard 7920-00-924-5700 TSEC/KYV-2A Secure Voice Module SVM 5810-01-160-4999
PCG-68 - Programmable Code Generator CSD-68 fill gun (Code Source Device?) AN/GRM-114A Test Set
This is an IFR Communications Service Monitor Model 1000S and appears to have no PRC-xxx customization TM 11-6625-3016-14 (051046.pdf) and others are on line at ETM
6625-01-144-4486 Vehicular mount/amplifier OF-185 5820-01-301-6301 Tool Kit TK-101/G 5180-00-064-6178 TS-3951/PRM-34 6225-01-094-5646 TS-3354 6625-01-091-3157 Frequency Transfer Cable (Cloning cable) 5995-01-201-1391 568698-801 Repeater cable none 56698-802 OE-254()/GRC Antenna Group 30 to 88 MHz 5985-01-063-1574 RC-292 antenna:
30-36.5, 36.5-50.5 or 50.5-79.95 MHz (not 80 - 88)
H-250/U Handset 5965-00-043-3463 5965-01-247-4723 H-138/U Handset 5965-00-892-0972 H-189/GR Handset 5965-00-069-8886 Ear Transducer (ear mic)
Earphone Transducer (EM-200)
H-157 AIC modified
Vehicular Adapter OF-185/PRC
30 -88 or 130 - 174 MHz depending on amp/fil
5820-01-301-6301 901602-801 Diplexer, VHF, CU-2194/URC
limited upper freq of 76 MHz
Radio ports are DC open - not good with PRC-xx
51859 755115A0000 Mofified Radio Shack 19-345 Simplex Repeater Controller Silicon Grease 6850-00-177-5094 68AA Antenna Adapter
w/built in Dc return
na na na na na 68BA Battery Adapter na na na na an
7.1 Manuals & LiteratureTM 11-5820-882-10 - Operator's Manual, PRC-68A (060365.pdf = Restricted)
TM 11-5820-882-23&P-1 (062081.pdf = Restricted)
TM 06827B-24/2- Technical Manual, Maintenance Instructions
Magnavox Presales sheet for Ancillaries Cables - showing the cloning and repeater (retransmission) calbes with no bumps, just cables.
7.2 Web LinksAN/PRC-68 Legacy by Alan D. Tasker, WA1NYR
PRC Data series by Dennis Starks
U.S. Military Portable Radios by By Alan Tasker, WA1NYR
Collecting Military Radios by Ralph Hogan WB4TUR
The Boneyard Radio Price Guide -
The PRC-25 Story by Dennis Starks
PRC-68-B by megaman
AN/PRC-126, Radio Set at Fort Monmouth
Non Tactical Portables at Army Radios web site
Communications Security and Related Equipment by Frederick W. Chesson -
Additional Comments by Dennis Starks on the Army Radio web page -
BB-388A/U, PP-8444A/U Charger, BA-5588U, 1588U, BB-588U
Datron World Communications MT1060MM 35 W RF booster amplifier, power conditioner, and power supply.
Audio Connectors & Cloning - Fill - Retransmission -
Military Radio Specifications - Radio Set AN/PRC-126 (RT-1547) -
Military Image Files - just a small gif image
*Crossing Linear Danger Areas* - how PRC-126 is deployed in a Squad
Soldiers of Fortune Ltd. - U.S. surplus equipment donated to the Bosnian mission include: 732 AN/PRC-126 handheld radios plus batteries, 1,600 AN/PRC-77 manpack radios with batteries
Ranger Training Brigade - Ranger Handbook TOC - Chapter Seven Communications - some operation and maintenance info
Center for Army Lessons Learned - Communications Equipment - "AN/PRC-126 Squad Radio worked well, especially in MOUT. Minor criticisms noted the audio signal for low battery and other functions which jeopardized position security and the need for an ear piece and whisper mike." - In Praise of Checkpoints - Squad use of PRC-126 and reporting check points - How to Turn Company Morters into a Combat Multiplier - Other small element leaders cannot quickly talk to the mortars without first finding a PRC-119. NOTE: Most squads carry the PRC-126, which does not frequency hop, and is not secure (? what about the SVM?, Brooke comment). This also lengthens mortar section response time.
Physics of Failure - AMXSY-LA UNCLASSIFIED 12 FEB 97 - Re-designs of ICAM, AN/PRC-126 and ARC-210 radios underway
Tobyhanna - Tactical Radio Division - Communications Security (COMSEC) Depot Opertions - Other INFOSEC Links -
C3 in the Maneuver Company -
"Use of non-secure radios (PRC 126/127s) is not allowed until contact with the enemy..." in search engine, but broken link
AN/PRC-117F Special Operations Forces radio has applications for digital divisions and beyond -
ALOG NEWS -Fort Bragg has established a central drop-off point for its 18 units that require repair support for their AN/PRC-126 handheld radios. Fort Bragg mails the radio components to Tobyhanna Army Depot, Pennsylvania, where they are repaired and mailed back to Fort Bragg. This system replaces the former practice of sending the radios through the regular supply system and cuts days off the turn-around time. The program began with the repair of circuit cards but has expanded to include other omponents, such as the PRC-126's frames and panels and its frequency synthesizer modules. Previously, these modules were thrown away rather than repaired.LRC Y2K Spreadsheet - the PRC-126 is Y2K compliant, it does not have a clock
Oral History Interview JCIT 0811LT JOHNSON: Well, get back to training, but again that's one thing that we didn't want to lose; lessons that we had learned. We took time and really wrote up a pretty substantial AAR which we got here. I have already noticed some ... one change come out of it. It was very minor point to put on the tape, but on the PRC-126 the little display panel is in green plastic. The idea behind that is so that it reduces the amount of light when you hit the display light at night. But in actuality, it makes it very hard to read any time either during the day or night. We have been trying to do this for awhile, but we just included in this after action report and that's what brought about the changes and everything. Now there is just clear plastic.Special Operations Forces Posture Statement 2000 - Appendix C Key Programs & Systems - ** Improved weight/size and power consumption by replacing numerous multi-frequency/banded, hand-held radios currently used (i.e., AN/PRC-68, AN/PRC-126, MX-300, MX-300S, and MZ-300R) with one full range/band radio
Specialty Defense Systems - Ranger Assault Carrying Kit (RACK) -
7.3 NIIN Text File (NIIN.txt)This is a file that can be used for searching the DRMS (Defense Reutilization and Marketing Service). It contains all of the NIIN numbers listed above in the Parts List.
7.4 Related Radios
The following radios are all in the PRC-68 family and use the same battery and secure voice module. They all use the common U-229 audio accesories.A power increase of 6 dB (1 "S" unit or 4 times) the wattage) is just noticable by the human ear, so a radio would need 4 Watts to just be louder than the PRC-68. Why would you want ot carry the weight of a PRC-25 or PRC-77 if you could have a PRC-126? Adding the OF-185/PRC amplifier results in a much more powerful vehicle mounted radio set.
They have a similar physical appearance.
- PRC-68 - 30 - 79.95 MHz
- PRC-68A - 30 -79.975 MHz
- PRC-68B - 30 - 87.975 or 130 - 173.9875 MHz by changing the RF/IF module
- PRC-126 - 30 - 87.975 MHz
- PRC-128 - 30 - 87.975 or 130 - 173.9875 MHz by changing the RF/IF module
- PRC-136 - 130 - 173.9875 MHz
8.1AUDIO J5 Pins
I have not been able to find any public information on Cloning or remote programming of the PRC-68A or any other radio in the Squad Radio family. Some of the following are experiments shed some light on this subject.
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Speaker MutingThe PRC-126 J5-B (audio out) is near 0 VDC when the radio is quiet and the DC level jumps to about +6 VDC when the squelch opens. The reason is to sense if an external earpiece is present. If so the speaker is muted.
Remember that the 1/4" phone plug does this mechanically, but with the MIL-C-55116 connectors there is no mechanical switching possible.
An AC coupled audio accessory with a high impedance DC voltage controled comparator could be used to detect when the squelch opens and be used for retransmission PTT control.
Pull Down Resistor Value for SPKR MuteWith resistance values greater or equal to 100 Ohms between J5-B (Audio Out) and J5-A (ground) the radio stays in internal speaker mode. With resistance values less than or equal to 25 Ohms the radio mutes the internal speaker.
(For the PRC-68 SPKR mute requires less than 3.3 K Ohms? thismay be a function of attery voltage?)
J5-C (Push To Talk)This has the same fuctions as the PTT switch on the radio.
J5-D (Microphone Hot)From J5-D to ground is ???150 Ohms. This matches the impedance of the H-250 handset.
This also is what provides the pull down resistance to cause the FILL mode to activate when an H-350 handset is connected.
J5-E (DC Power)To use external power set the OFF-ON-SQUELCH DIS switch in the OFF position. That turns off the battery and connects to the External power.
page created since 29 Oct. 2000.