Survivalism & Self Sufficiency Topics > The HAM Radio Board

Encrypted MURS Voice Communications?

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DeltaEchoVictor:

--- Quote ---And, while we both know that encryption over amateur radio is illegal, in a TEOTWAKI situation, we might think differently about it.
--- End quote ---
Exactly.

Since all radios can be modded to tx out of band...hypothetically of course....in an EOTWAWKI situation all bets are off.  One does what one needs to when the end is nigh.  I'm thinking along the lines of predetermined contacts, nets, & what not that one might not want to advertise over the open air & talking on off band predetermined dead(er) frequs might be the way to go.  Much to my delight you're working on the problem it appears. ;)

docred:
The concept of a affordable consumer encryption for radios is pretty appealing.

The Professor:

--- 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")?

My Answer: Yes.  Absolutely.  For those who argue with this, I might suggest learning how to converse properly over comms.  The military has done it for decades. 

2.  Would it be useful to have an "CALL" or "ALERT" button that would "ping" the other stations in your encrypted comm net?

My Answer: Absolutely.

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?

My Answer: Hell yes. . .especially if you could also make it work with, say, a Blackberry via the mini-USP Port.  (hint, hint)

4.  What kind of battery life is reasonable?

My Answer : 2-3 hours of talk time would be more than sufficient with, say, double for stand-by.

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?

My answer: How about both?  Offer an adapter that takes common batteries and allows them to be used.

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?

My Answer : Hell yes.

But I would also ask you how you load the keys in.  Having a keyloader would be super, especially for large numbers of encryption units.  Don't make them Clonable (sp?) from one radio to another, though.  Fix it to where you must have a keyloader to set the encryption key for each radio, otherwise you face the risk of someone getting a device and cloning their device to your keys.

Dude, if you're this handy with electronics, we do need to talk.  I have a couple of other ideas for some fun, useful equipment that the preparedness-minded individual may get a use out of!

I will be honest, I am definitely envious of your skills.

The Professor.
--- End quote ---

ejsandstrom:

--- 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 ---

1. YES
2.YES
3.OH HELL YA
4. No matter how long it is, its never long enough, do your best.
5. Why cant you have both. 2 AA batteries is 3VDC in series dosent a USB put out like 5VDC? It could come with rechargeables, then offer one of those small solar panels that fold up. now you have almost infanate possibilitys for power.
6. YES

backwoods_engineer:
Sister Wolf, thanks for your comments and interest.  I'll answer your questions below.


--- Quote from: Sister Wolf on February 25, 2009, 08:37:25 PM ---1. How much more expensive would it be to have better than cell phone quality audio?  Cell phone quality isn't all that great, and I'd like to feel absolutely secure that I understand everything that is being said to me over the radio.

--- End quote ---
Though it pains me to disappoint so gracious a lady, I fear I must do so.  This is a matter of technical limitations of the radio in question, not the module I am proposing.  You see, those radios don't have very much signal bandwidth, and I need extra in order to encrypt and encode your voice.    It really will sound quote good, as I will show you, but let me explain what is going on.

Remember how "on-hold" music through a telephone sounds "tinny"?  That "tinniness" is due to a bandpass filter reducing the available bandwidth.  Since I have to add encryption to the voice signal, that causes it to have more bandwidth.  Therefore, I will use a computer algorithm called a "vocoder" to reduce the bandwidth of the voice, so I still have room to add encryption and other "overhead" data, and it will still fit in the signal bandwidth of the MURS or FRS/GMRS radios.  The vocoder doesn't cause the voice to have "tinniness", it just gives the voice a slightly "digital" quality that is still quite understandable.  All cell phones these days use vocoders.

I can give you an idea of how my module will sound, because I am planning to use the open-source Speex vocoder:
Here are two voice samples BEFORE the vocoder operates on it: http://speex.org/samples/audio/male.wav  http://speex.org/samples/audio/female.wav
Here are the same two voice samples AFTER they have gone through the vocoder and decoder: http://speex.org/samples/audio/male_speex_4.wav http://speex.org/samples/audio/female_speex_4.wav

To my ears, there is very little difference, and the audio is quite clear.

By the way, if a radio user WITHOUT a COMSEC module were to listen to the channel, he/she would hear something similar to this:  http://www.kb9ukd.com/digital/152.33-taxi.wav. 

That's a 4800-baud QPSK signal, for the techies out there.  My information says that MURS has the bandwidth for this, but FRS/GMRS may only support 2400 baud.  If so, then the voice transmissions over FRS/GRMS may be delayed slightly from "real time", to allow the slower data rate to convey the voice.  Most times, with short transmissions, the delay would only be a second or so, and you really wouldn't notice unless you were standing right next to the sending radio.


--- Quote from: Sister Wolf on February 25, 2009, 08:37:25 PM ---4. I would feel really good knowing that my radio was going to last at least 12 hours at full strength.  That way, I could replace the batteries every night, and again every morning (if it comes to needing the radio to be on constantly)

--- End quote ---

I think the battery life will depend on how much you're transmitting (coding requires more battery power than decoding), and how much the channel is just quiet.  If it is quiet, my device won't pull much power from its battery at all.


--- Quote from: Sister Wolf on February 25, 2009, 08:37:25 PM ---5. Please please please please PLEASE make it run off of something I can use my Solio to recharge.  If I'm hiking my butt home, because the freeways are too clogged to drive on, and therefore have absolutely no way to use a laptop for very long, I will thank you a thousand times over, when I'm able to recharge the batteries WHILE I'm hiking home.

--- End quote ---

Of course!  Solio has a USB port charging connector.  Ah, a thousand thanks from the gracious lady!


--- Quote from: Sister Wolf on February 25, 2009, 08:37:25 PM ---PS - what's an "in ear mike"?  Is that like what the secret service dudes are always using, with the little coily thingie coming out of their ear?

--- End quote ---

To my best understanding, it is a combination mike/speaker that picks up most of the voice through bone conduction, and therefore is less sensitive to outside noise than a regular mike.  Yes, I think the SS uses them.

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