Ever since reading Witherbotham's 1973 book "The Ultra Secret" I've been fascinated by cryptography and have purchased a number of crypto machines. I also have a interest in both civilian and military telephone systems.
In the book Crypto: How the Code Rebels Beat the Government - Saving Privacy in the Digital Age by Steven Levy there is a chapter on The Clipper Chip.
The first version of this device made use of the DES (Wiki) algorithm but the NSA (Wiki) wanted a way for law enforcement to listen to some conversations when they had a court order so developed the Clipper Chip (Wiki) key escrow (Wiki) system, aka a Back Door (Wiki).
It is not a telephone, but rather it is an audio processing device that fits between the telephone set and the handset. The out of the box hardware thus only works on phones that use a modular handset cord. But it may be possible to use an adapter for other audio devices, like military radios.
Fig 1 Buttoms for Clear and go secure.
Fig 2 Side and back connections
Note rear Handset Module floor plate is cockeyed.
Fig 3 Bottom - Label
Fig 4 In the Box
Handset Modules HM1, HM2 & HM3
6VDC @ 800ma power supply
short handset modular cord
Instruction Manual & quick start guide (not shown)
Fig 5 Handset Module HM-1
This is important because the different types of microphone (Wiki) have different circuit requirements and you can not replace one technology by just connecting a different one. Hence the need for the different Handset Modules. There's a possibility that the speaker part of the handsets differ in their drive impedance requirements and so that would be another factor that might be part of the Handset Module. They have an impedance at 1 kHz that varies between 150 and 600 Ohms.
The early telephone used a carbon granule microphone (Wiki). These were used in all telephones ( 202, 302, 500, 2500) made by AT&T while they are still AT&T. Carbon mikes were also used in military equipment through the Korean conflict (Wiki) and part way into the Vietnam era (Wiki). Military equipment that used 1/4" phone plugs or the U-77 audio connector worked with carbon mikes. Carbon mikes require a bias voltage (or current) so that as the carbon changes resistance a voltage will be produced.The carbon transmitters used in F and G handsets are covered in BSP C18.059-i1
But electrical specifications are not part of the BSP nor are circuit details.
Dynamic microphones replaced carbon microphones in military radios and telephones. These use the U-229 audio connector (which is also used for crypto fill and other things) and are NATO standard devices today (2014). It turns out the Bell's Gallows Phone was used a single mike/speaker that was a dynamic type, but it did not have as much gain as the carbon mike so was not used in the early phone systems. Dynamic mikes use a permanent magnet and moving coil of wire (just like a loudspeaker (Wiki)) and so not not need any bias voltage. If a bias is applied under some circumstances the bias will cause audio distortion.
The Electret microphone (Wiki) in it's pure form does not need any bias voltage, but the modern Electret mike element contains a FET (Wiki) which does need DC bias. These mike elements are small and inexpensive and so are used in many modern microphones which includes telephone systems.
Table of Handset Modules
Note the HM1, HM2 and HM3 modules are included in the box along with the power supply, User's Manual, .....
R [BSP: 501-210-130 I1]
AT&T Merlin, System 25, System 75, System 85
K [BSP: 501-210-105-i1-K1A-Handset Tl]
LB receiver [BLR P220]
Carbon mike with conventional networks
Electret on low cost "Traditional 100"
CS2500 and CS2554 series sets.
AT&T Merlin Legend, Partner, Residential
Comdial, Contel, Hitachi, Isotec, Intecom, ITT, Iwatsu, Northern Telcom, NEC, Norstan, Seimens, Toshiba, Vodavi, Harris
G [BSP: 501-210-102 I9]
Used on: 500 & 2500 telephones
Northern Telecom, Comdial, ITT, Intecom
GE, CodaPhone, Fujitsu, Panasonic
Electroacoustic transducer,Gerhard M Sessler, James E West (Bell Telephone Labs), Jan 14, 1964, 81/191, 307/400, 55/DIG.390, 381/398
Western Electric 202 dial phone
Bell System 302 dial phone
Bell System 500 dial phone
Bell system 2500 Touch Tone phone
Panasonic KX-TA824 Small Business Phone System (PBX)
VOIP Voice Over Internet Protocol
EE-8 Army Field Phone
F91120 BER Test Set
Fullerphone Telephone Set D Mk 5
GRA-39 Radio Set Control
GRA-71 Coder-Burst Transmission Group
M-94 Cipher Wheels
MATEL 2C800 Field Phone
MSC2001 Voice Encryption Unit (VEU)
KD-100 Key Tape Disintegrator
KY-38 Secure Voice System
KY-57 Transmission Security Device
KY-65 Narrow-band Secure Voice Unit
KY-68 Digital Subscriber Voice Terminal
KY-99 Advanced Narrowband Digital Voice Terminal (ANDVT)
KYV-2(A) Secure Voice Module SVM68
MX-18290/VRC Fill Device, ELEK CCM
PLGR AN/PSN-11 GPS Receiver
Quantic Q-5200/SM Timing GPS Receiver
SB-22 Field Switchboard
SB-4170 /TT Switchboard
TA-1 Sound Powered Telephone Set
TA-312 Field Phone
TA-838/TT Field Telephone Set
TA-1042A/U Digital Non-Secure Voice Terminal (DNVT)
TCC CSD 909 PRM Communication Security Device
TG-5 Telegraph Set
Trimble SAGR, AN/ASN-169
USM-481 VINSON Interconnect Test Set
I have way too many military radio web pages to list here.
Brooke's: PRC68, Alphanumeric index of web pages, Contact, Products for sale,
This page created on 15 Aug 2014