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Covert, Secure, Off-Grid Communications
closed-circuit telephone: 
A telephone on a circuit that provides telephonic communication within a limited area, such as a single building; it 
accepts no incoming calls from the outside nor can calls be made to the outside. Also called a house telephone or 
house phone.
While it is not "impossible" to intercept calls on a closed-circuit system, it is infinitely more secure than either a 
public hard-line or cellular system. given today's technology, it is sometimes wiser to go low-tech rather than high. 
Communications intercept equipment is usually geared and upgraded for ever INCREASING technology. Going 
lo-tech while maintaining a false-flag operation on conventional equipment may be just the thing.
Sound-Powered Telephone Systems: 
So, having done a little research, I figure the most secure system would be a closed-circuit sound-powered 
telephone system. Little or no EM signature (non when not in use, negligible when using) and - properly laid - 
almost impossible to detect or tap.
From Wikipedia, the free encyclopedia 
http://en.wikipedia.org/wiki/Sound-powered_telephone 
A sound-powered telephone is a communication device that allows users to talk to each other with the use of a 
handset, similar to a conventional telephone, but without the use of external power. This technology has been 
used for at least six decades for both routine and emergency communication on ships to allow communication 
between key locations on a vessel even if power, including batteries, is no longer available. A sound-powered 
phone circuit can have two or more stations on the same circuit. The circuit is always live, thus a user simply 
begins speaking rather than dialing another station. Sound-powered telephones are not normally connected to a 
telephone exchange.
The headset microphone transducer converts sound pressure from a user's voice into a minute electrical current, 
which is then converted back to sound by a transducer at the other end. The most significant distinction between 
ordinary telephones and sound-powered telephones is in the operation of the microphone. Since the more 
common carbon microphone used in most telephones does not convert acoustic energy to electrical energy (it 
only modulates the supplied electrical current) it cannot be used in sound-powered transducers. Rather, most 
sound-powered telephones use a dynamic microphone. A common approach to transducer design is the balanced
armature design because of its efficiency. The number of simultaneous listeners is limited because there is no 
amplification of the signal.
A sound-powered telephone circuit can be as simple as two handsets connected together with a pair of wires. 
More complex circuits include magnetos, selector switches and bells to allow one user to select and call another. 
The voice communication circuit is completely separate from the call circuit, allowing communication to take place 
without external power.
The US Navy training manual on these systems should be sufficient to figure out what is necessary, equipment 
and operations-wise, and a bit of ingenuity in the layout of the system can make it invisible.
Sound-Powered Telephone Talkers' Training Manual NAVEDTRA 14232
CONTENTS
	1. Introduction to Sound-Powered Telephones . . . . . . 1-1
	2. Sound-Powered Telephone Talker Procedures . . . . . 2-1
	3. The Sound-Powered Telephone System . . . . . . . . . 3-1
	4. Sound-Powered Telephone Exercises . . . . . . . . . . . 4-1
APPENDIX
	I. References Used To Develop This TRAMAN . . . . AI-1
Another interesting page covering a 1940's WW2 Navy Manual can be viewed at:
Stay Tuned Website http://www.crystalradio.net/soundpowered/rcamanual/index.shtml
Response:
Hi All,
Don't throw away those old "pulse dial" telephones yet! Designed to work on 48VDC, they will work on 12VDC 
depending on the distance, and thickness of the twin wire you use. My Dad (who worked for Rochester Telephone 
- now Frontier) for 34 years had a closed circuit phone system rigged between the house, the wood shop, and my 
radio shack when I was a kid. Just a twin lead wire rigged between the three places with a 12v battery in parallel 
with the line. The pulses that the phones produced rang the other phones bells lightly, but clearly. 1 pulse rang 
the bells once, and so on. Each phone had to have an earth ground for lightning protection. The system worked 
for years.
Regards
Reply:
	Thanks!
	I always wondered where the power was coming from with phones - 
	they work when the power is out - and what their requirements were. 
	Obviously, not enough to find out... Researching Ma Bell type 
	systems is a major pain via google, et.al. All sorts of blind trails and 
	techno-speech.
	I don't suppose we could impose on you to provide a line drawing of 
	the basic circuit? Sometimes see it is more revealing than reading it. 
	Put both together and it becomes easy.
Response:
Meg,
I don't remember how Dad had the circuit wired up, but I imagine it was like the sound powered systems we had on 
board ships in the Navy. I will look for a link to one. I suspect that the contacts in the older pulse driven phones 
may have to be re-wired to use DC power without the relay systems used in the local exchanges of old.
The advantage to this type of phone system would be to wire agreeing parties in an apartment complex, or use a 
closed system between houses in a small area. Another advantage would be having a comm system that does not 
radiate RF into the airwaves that could be intercepted.
I will do a Google search, and a Wikipedia search - those two would be the most productive. Next post will show 
results of my search. Hopefully a link direct to the info.
Anyone who needs info on how to set up a "listening post" to receive outside news via shortwave, or scanner, or 
both - I would be happy to help out. Thirty years as a Navy Radio operator, and as a Ham Radio Operator should 
be enough experience to help out?
Best Regards!
Reply:
	Oh, Man!
	You have no idea how long I've been looking for a qualified RTO! Boy, do I 
	have a lot of questions for you... {grin}
	Thanks for the info - it's good to see someone else who likes to do research. 
	Lord, it is frustrating getting qualified results, sometimes. Perseverance helps, 
	but all the garbage that is out there - the eyes and fingers can only take so 
	much. I was going to copy (to PDF) the "RCA Sound Powered Manual" I found 
	at http://www.crystalradio.net/soundpowered/rcamanual/index.shtml, but I 
	haven't even had a chance to read/scan it yet.
Response:
Meg,
Yes, I'm sort of an expert at radio communications, especially how the Navy looks at communications. Be glad to 
answer any questions for you or the group.
The best "listening post" is where you do not transmit much of anything - unless its a dire emergency. I haven't 
found a layman's site about closed circuit telephones yet, but I will - even if I have to diagram it myself. Its the
conversion of the old pulse dial phones that is the problem, they were designed for 50 to 75 volts DC, yet I
remember old style field phones that used two "D" cell batteries that reached for miles (or as much twin lead wire 
as you had).
The old railroad telegraphs used to use one wire, and a ground stake for their system. I'll be looking for the old 
phones myself, and try to work this out. Wish my Dad was still around, but he passed in 1994. He would make me 
feel stupid as to how to do this. More later...

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