Survivalism & Self Sufficiency Topics > The HAM Radio Board

Encrypted MURS Voice Communications?

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I got my hands on 2 Motorola Nextel/Sprint cellphones that have the Direct-Talk feature. (Motorola i560 & i670)

Even if you cancel your contract, you can still use them in the DT mode since you are using them like a walkie-talkie and not using the cell network.

I haven't tested the range, but it's probably around 1/4 mile or so. The only thing with digital communications is the 1/4 second delay you have to wait when you push to talk before you start speaking.


--- Quote from: backwoods_engineer on February 25, 2009, 07:04:54 PM ---Okay, guys, thanks for the feedback so far, but I have some more questions:

1.  If the voice was clear, would cell-phone quality audio be acceptable (kind of "digital-sounding")?
2.  Would it be useful to have an "CALL" or "ALERT" button that would "ping" the other stations in your encrypted comm net?
3.  Would it be useful to be able to do encrypted messaging with the other members of your net by plugging the encryption module into the USB port of a laptop?
4.  What kind of battery life is reasonable?
5.  Do you think the USB-rechargable internal battery is a good idea, or should the thing run off something replaceable, like an "AA" cell?
6.  Would it be useful to have button(s) to switch between two (or more) encryption key numbers, to allow for multiple nets or to "kill" compromised radios?

Your thoughts, please, survival mavens...

--- End quote ---
Great concept! I love the idea! Yes, proper commo training is needed to ensure security is not wasted, but alas, that's a training issue. SS is the way to go if possible as I believe RDF is under 2 sec. now.

Here's my take on your questions:
1. Cell quality is acceptable.
2. Call button pings are nice as long as noise discipline is maintained.
3. Encrypted messaging thru a laptop is cool. Encrypted messaging via a module to another module on another radio is cooler.
4. 1 common battery change per 24hr continuous stand-by period, and 12hr talk time is acceptable to me.
5. I like rechargeable battery packs (with no special stands) that can be pulled out & replaced by a caddy that holds regular AA batteries. My field solar rechargers laugh at the idea of special battery sizes & voltages.
6. Multiple encryption codes would add a nice versatility. Code reprogramming must be able to be performed without the need for a laptop. Perhaps a key module could also be made. An emergency zero key would be nice, but must be idiot-proof.

Even with encryption, I'd still use one-time pad brevity codes just to stay in practice.

I think some of the arguments mentioned above concern different perceived threats: (and are treated differently)

1. If the threat is an oppressive .gov (like China) that is in a pissy mood & is ready to squash anything that looks at it wrong, then end-users should know this and not use encryption if it might provoke genocide vs. it's innocent citizenry. In such cases, common phrase one-time pads are indicated.

2. If, on the other hand, the threats are gang-bangers trolling the civilian bands looking for easy targets in a crisis, then encryption is certainly the way to go. (provided #1 above is not also in play at that time)

Moral of the story? Know the threats arrayed against you, and secure your communications accordingly.

Basic Stamp - PIC Portable Program Module.

Could you use the PIC or similar system to build a PC-less programmer?  I don't know if you have seen it or not, but NUE-PSK has a nice little PC-less PSK31 modem.  All you need is the radio, keyboard and the unit.  It is Field upgradable using the new USB module they have, and run pretty nicely.  I have one, though I have not used it recently.

I don't see why you could not build a FPM (Field Programming Unit) that could interface / Charge / etc the SecCom (Security Communications) Unit.

I think what you are proposing is a good idea, and I'll step in line to pony up and test the unit for you.  My Elmer and best friend has told me a number of times that I am a "Conceptual Engineer"...  I can think it,.. Test it, ... and a lot of times break it.. (lol) But I can't engineer it.  I can solder, and I have hack a few things here and there (cell phone battery converted to a Kenwood HT battery pack...)..  So I do know a bit.. 

I really hope you will continue your work,.. 


I like the concept, I'm still not sure of the legal aspects though. I know the subject is MURS, NOT FRS, but if its ends up in the FRS market please consider the following.

95.193 (FRS Rule 3) Types of communications.
later half of subpoint (2)

Digital data transmissions shall not exceed one
       second, and shall be limited to no more than one digital
       transmission within a thirty-second period, except that an FRS
       unit may automatically respond to more than one interrogation
       request received within a thirty-second period.

 95.194 (FRS Rule 4) FRS units.
(c) You may not attach any antenna, power amplifier, or other apparatus to
    an FRS unit that has not been FCC certified as part of that FRS unit.
    There are no exceptions to this rule and attaching any such apparatus
    to a FRS unit cancels the FCC certification and voids everyone's
    authority to operate the unit in the FRS.


When I got a few minutes I did a bit more research.  MURS allows digital, but only for radios with Built IN digital.
MURS does not allow add-ons.

FCC Rules require that you transmit on a MURS frequency only with a radio model certificated for MURS. You may transmit data communications in MURS only if the radio is certificated for data communications, or of those transmissions otherwise comply with the rules and those transmissions can be imposed on a conventional voice emission. You may not make any internal modifications or additions to a MURS radio to transmit data communications.

The only way around this that I can see if the encryption circuity would have to be included at the time of manufacture of the radio so that it is FCC certified.  There does not appear to be a way to get an external add-on certified. 


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