The PRC-25B was a PRC-25 that had a wide band audio modification made to support digital voice encryption and multicall digital telephony. The PRC-25B modification established the pin connections for the "POWER" (now also an X-mode) connector used on the PRC-77. The PRC-77 also replaced the final RF amplifier tube of the PRC-25 with a solid state RF amplifier to increase reliability and lower power consumption.
The outer appearance, radio functional operation and accessories are identical to the PRC-25. To learn about the PRC-77 you need to find out more about he PRC-25. The PRC-77 is really a PRC-25B with a solid state final amplifier.
The PRC-68, PRC-68A, PRC-68B, PRC-126 and PRC-128 (with the VHF low band module) hand held squad radios have the same functionality as the PRC-77. When the KYV-13 Secure Voice Module is added to the hand held radios they will interoperate with the PRC-77 (or PRC-25B) when used with the KY-57 Voice Encrytpion Uint.
The PRC-77 when can inter-communicate with the SINCGARS radios, and when a KY-57 is used with the PRC-77 it can also communicate with the SINCGARS radios when they are in the COMSEC mode oralso using a KY-57.
The Receiver-Transmitter is the RT-841/PRC-77.
There is a 25 kHz channel spacing version called the PRC-2841.
The AM-4306/GRC is one of the external RF amplifiers that can be used with the radio. The AM-4477 is another of the RF amps. Both of these are packaged in a housing very much like the radio.
Man pack configuration.
TM 11-5820-667-12 - Opertor's and Organizational Maintenance Manual, Radio Set AN/PRC-77, (NSN 5820-00-930-3724), (Including Receiver-Transmitter, Radio RT-841/PRC-77), NSN 5820-00-930-3725), 1 Jan 1987 Change 1
TM 11-5820-667-20P Parts that are easily replaced like modules, accessories and front panel includes the AS-2109 Antenna.
TM 11-5820-667-34P - Repair Parts & Special Tools - 1978 - 215 pages w/ info on all the modules
TM 11-5820-667-34P - Repair Parts & Special Tools - 1989 - 74 pages no module information
TM 11-5820-667-34LD - Plastic Laminated Diagrams for Direct and General Support Maint for RT-841/PRC-77
TM 11-5820-667-35 includes schematics
The Change 2 manual is the same as the Change1 manual except the C2 has a lot of added info typically about different versions of the modules. Change 3 that's on LOGSA has had a lot of informatin removed including the overall schematic and is not of much use.SB 11-660 - Recoverability Code for Modules
VRC-64 & GRC-160 Manuals
A vehicle only installation of the PRC-77 is called a VRC-64. If the parts needed for a man-pack setup are included with a VRC-64 then it's called a GRC-160. The following manuals have a lot of info on the AM-2060 & VIC-1 plus related items, but not on the radio itself.
TM 11-5820-498-12 - Operators & Org Maint Man
TM 11-5820-498-20P - Org Maint Parts
TM 11-5820-498-34P - Repair Parts & Special Tools
TM 11-5820-498-35 - DS, GS & Depot maint
The Z1 (GC U-317/U) jumper plug must be connected for the radio to work from the battery.
If your's is missing I could make a functional equivalent based n the same plug used for the VPA-2577 Vehicle Power Adapter cable, but this would just look like the plug with no wires. If interested let me know.
Military batteries like the BA-5598/U LiSO2 primary, the BB-586 Ni-Cad will work. I think that it's hard if not impossible to get a working BA-4386/PRC-25 Magnesium battery.
My 257477BA Battery Adapter allows the use of 10 common "D" size batteries.
The BA-5598/U LiSO2 battery is half the size of the BA-4386/U Magnesium battery so two of them can be used in the battery box, one active and one spare. Note that only the Chemtronics LS 91 or LS 94 can measure the State Of Charge of LiSO2 chemistry batteries, ALL the other battery testers can NOT measure the condition of these batteries.
The Straight Plug is an Amphenol Aerospace MIL-C-26482 Series 1 Bayonet, Solder connector PT06A-12-14P(SR) where the SR suffix adds Strain Relief that's in Amphenol catalog 12-070. 21 Nov. 2003 - This is used on my VPA-2577 and CLP-77 cables.. Many of the military cables use the U-316 plug that has a long strain relief.
VPA-2577 Vehicle Power Adapter CableWARNING - It's hard to read which pin is which letter on this connector. "B" is the pin closest to the wide locating ridge and "A" is next to "B". The schematic (back a few pages from the end) in the PRC-25 manual TM 5820-398-35 shows J3 with pin "B" at the top and is correct.
Many of the military cable plugs that mate with the PRC-77 POWER receptacle are the U-316/U. This cable plug is designed for the conduit type cabling used when encrypted voice mode is in use. The outer sheath is a hollow conduit and individual wires are used inside. The conduit provides better shielding for TEMPEST and EMP then the braided shield on some cables.
- Pin A is ground
- Pin E has the vehicle "12 Volt" power.
With the Vehicle Power Adapter cable it's easy to measure the current:
PRC-77 U-383/VR Power Supply adapter made by Artisan Electronics Corp. This looks like a stock CY-2562 battery box but will take in 12 to 30 VDC and supplies the radio 12 to 15 VDC to allow use from a military vehicle 24 Volt system.
Note it does not have the filament supply to support the PRC-25 but it can be added.
Basic Radio IssueRT-841/PRC-77 Receiver-Transmitter
CW-503 Accessory Bag with:
AB-591 Spring Base & AT-271 Fishing Pole Antenna
P/O AT-892 Gooseneck & AT-892 Tape Antenna
Optional AccessoriesSee the PRC-25 accessories, sine the radios are almost identical
MT-3823 Shock Mount
AM-4477 Range Booster optionally with CY2577 DC Power Supply for use in AM-2060 with MT-1029.
Test Adapter for the POWER connector
F91120 Bit Error Rate Test Set
KY-57The KY-57 Voice Encryption Unit that interoperates with the KYV-2() Secure Voice Module on the PRC-68 family of radios
The CX-12991 cable connects the KY-57 to PRC-77 interconnect cable NSN 5995-01-058-2513 W15P7T-91-S7101 cage 55928
Mfr/pn: SM-D-598871, apr '92
Prior to the KY-57, the PRC-77 was used with the KY-38 Voice Encryption Device.
PRC-77 Description PRC-77 Power pin KY-57 Radio pin KY-57 Description Ground A G Ground Narrow audio out B C Rx audio in (for PT) PTT to radio C S gnd to key radio (Send) audio to radio D M Tx plain audio in +15 V to radio E (jmp F)
+ 15 V from batt F(jmp E) nc nc H nc Mike ground J L Tx plain audio gnd Retrans out
gnd for Crypto1
L E = T na M nc +15 during Tx
Wide Band audio out P A Rx cipher in Wide Band audio in 2
R D Tx cipher out nc B nc F nc H nc J nc K nc N nc P nc R nc U nc V
1 - Grounding pin L disables the handset mike audio so only the external wide band input on pin R drives the modulator.
2 - The modulator is AC coupled and passes roughly 220 Hz to 220 kHz, is not DC coupled.
The PRC-77 and a KY-57 can be carried by one man using the LC-2 pack frame, a couple of cargo shelves and 4 each load straps.
When the KY-38 was used, it was more than one man could carry and there were a lot of problems related to the cable connecting two soldiers each carrying one of the items.
MSC-2001This Voice Encryption Unit (VEU) is made by Seimens in Germany and was designed to work with the PRC-77. This may be related to export restrictions on the KY-57. It's Ts/Rx and REMOTE connectors are identical to the PRC-77 POWER connector and many of the pins have complementary functions, so a number of them can be wired 1 to 1 for an interconnect cable.
|Module #||Module Function||SMD #||Rev "A" ?||SMD #||PRC-25?||PRC-77?||PRC-377 25 kHz||PRC-25T 26-71|
|A1||DC/DC Converter||447269||yes||not needed|
|A2||PA Tank||447620||yes||repl/w A32|
|A3||1st Rx RF Amp||447555||yes||repl/w A33|
|A4||2nd Rx RF Amp||447556||yes||repl/w A34|
|A5||Rx Mixer||447462||yes||repl/w A35|
|A6||Tx IPA||447557||yes||repl/w A37|
|A7||Tx 2nd RF Amp||447558||yes||no|
|A8||Tx 1st RF Amp||447559||yes||no|
|A10||Interval Oscillator||447407||yes||repl\w A40|
|A13||53 MHz Filter||447448||yes||repl/w A43|
|A14||1st Mixer||447449||yes||repl/w A44|
|A15||1 MHz Spectrum Gen||447450||yes||repl/w A45|
|A18||5.6 MHz IF||447453||yes||?||yes||yes||A18A||A18|
|A19||1/4 Wave Network||447454||yes||no|
|A21||Rx IF Limiter||447177||yes||875724||yes||yes||A21A||A21|
|A24||Tone Squelch||447318||yes||repl/w A54|
|A25||Rx Audio||447113||yes||repl/w A55|
|A31||Tx Frequency Control||?||no||yes||A331||A31|
|A33||Rx 1st RF Amp||?||no||yes||A33||A133|
|A34||Rx 2nd RF Amp||?||yes||?||no||yes||A34||A134|
|A43||53 MHz Filter||448739||no||yes||A43||A43|
|A45||1 MHz Spectrum Gen||448750||yes||?||no||yes||A45A||A45|
|A60||Wide Band Attenuator||?||no||yes||?||?|
New Radios Improve Afghan Army Communications -PRC-77 used by Afghan National Army
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