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Old 10-26-2010, 07:03 AM
Optimistic_Pessimist Optimistic_Pessimist is offline
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Default Secure 2 Way Radio (oxymoron?)



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Hi All,

I am after a two way radio set, to communicate amongst a small group or between our house and the lookout point.

I know most 2 ways have channels and privacy codes, but that doesn't stop anyone listening in.

Can anyone recommend a 2 way radio that:

1. VOX and ear jack
2. Decent battery life
3. has some sort of scrambler (is that the right term?) or encryption, so that other people can't listen in?

Any help would be much appreciated as I've been surfing for hours trying to find out and can't find anything.

Cheers,
O_P
Old 10-26-2010, 09:47 AM
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Your going to be hard pressed to find radio service you can legal use an encryptor on.
Its not legal on the ham bands, FRS, GMRS, MURS or CB.

You can get a business band radio license and use encryptors and scramblers but encyrption is expensive.

If you need a short range radio, The trisquare 900mhz radio will meet your needs.
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Old 10-26-2010, 10:56 AM
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First of all, any radio emission can be tracked to its source with a relatively inexpensive foxhunt setup. So code or no code, your position is discoverable.

I don't see much of a purpose in codes unless TSHTF in a way that involved socio/political/economic/civil collapse. And if that's the case, both we and what remains of the govt. will have much more on our hands to worry about than codes.
Old 10-26-2010, 12:29 PM
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Just learn and use Morse Code. Unless that one guy that happens to be in the command post at the time is listening (Amazing how that happens in movies) there's a pretty high probability that no one will know what you're sending. If you want to make up your own language, code makes it that much harder for someone to break.

Ohh, or find an enigma machine.. That's the ticket..
Old 10-26-2010, 12:33 PM
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Learn Navajo, Japan still hasn't figured it out.

That or get a Ham repeater set a custom offset, and make it private.
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Old 10-26-2010, 01:38 PM
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The offset is just the difference between input vs. output frequencies. And PL-tones are just added tones (there's a dozen or so common ones) to limit traffic a bit -- not unlike the so-called privacy squelch modes on some FRS/GMRS radios. All of this can service to limit noise, but it won't really make things private from eavesdropping.

But that's one of the good things about amateur radio. Free, open, non-commercial, dedicated hobbyists. Think of all the spam on the internet. Wouldn't take too many bad apples to ruin entire bands.

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Originally Posted by SgtBooker44 View Post
Learn Navajo, Japan still hasn't figured it out.

That or get a Ham repeater set a custom offset, and make it private.
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Old 10-26-2010, 02:00 PM
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If it's very short range,.. any radios that can make the distance might work..
They can be located, but,..
Communicate in your own proprietary language. Numbers, letters, etc.

"12,..42 , alpha55, 03, "

You could be located but not understood. Crude, but would probably work. Who would have the resources to 'crack' your code?
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Old 10-26-2010, 02:27 PM
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You'll need something like this

http://cgi.ebay.com/Motorola-XTS3000...item27b5e2cfda

Then install one of these
http://cgi.ebay.com/Motorola-XTS3000...item27b5e2a25e

Then get you one of these
http://cgi.ebay.com/Motorola-XTS3000...item27b5e2a25e

Figure out how to use it and you're all set.
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Old 10-26-2010, 02:37 PM
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Quote:
Originally Posted by SgtBooker44 View Post
Learn Navajo, Japan still hasn't figured it out.
Wouldn't have to be as exotic as Navajo. (Although I suspect the Soviets had a Navajo Academy somewhere )

One way would be to use the police 10-codes but change the numbers around. Or speak the numbers in Navajo; or in Kadazan-Dusun.
Old 10-26-2010, 04:56 PM
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Or use lasers. But they are quite directional.
Old 10-26-2010, 05:12 PM
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You could also use a book that both groups have and just use page, paragraph, and numbers to indicate what page, paragraph and word you want to say. It can take a bit to set up but, there will be a long enough pause that whoever is listening might start searching the bands looking for the response.

That brings up another idea. Reply on a different frequency or band.

Both ways will take some preplanning but, if you absolutely need to be secure, that's about your best bet.
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Old 10-26-2010, 09:03 PM
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Known as a one-time pad in the crypto field (http://en.wikipedia.org/wiki/One-time_pad). Extremely effective if used properly.

But keep a few things in mind:
1. Not allowed in the amateur service.
2. Your signal can still be traced by foxhunt.
3. Someone who's broadcasting a lot of coded material is merely drawing attention to himself, suggesting he's got something serious to hide -- and therefore makes himself a target. Not for cracking the code, but for an uninvited guest of one kind or the other.

Quote:
Originally Posted by kl0an View Post
You could also use a book that both groups have and just use page, paragraph, and numbers to indicate what page, paragraph and word you want to say. It can take a bit to set up but, there will be a long enough pause that whoever is listening might start searching the bands looking for the response.

That brings up another idea. Reply on a different frequency or band.

Both ways will take some preplanning but, if you absolutely need to be secure, that's about your best bet.
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Old 10-27-2010, 10:52 PM
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The ham radio folks have dreamed up lots of ways to transmit. The most interesting ones these days are phase shift keying. Not a code or encryption, but a different way to modulate your signal that is resistant to noise.

If you dream up a new one and publish the details it is legal to use. Not your problem if the average Joe does not read QST.
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Old 10-28-2010, 12:28 AM
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Quote:
Originally Posted by WSierra View Post
If it's very short range,.. any radios that can make the distance might work..
They can be located, but,..
Communicate in your own proprietary language. Numbers, letters, etc.

"12,..42 , alpha55, 03, "

You could be located but not understood. Crude, but would probably work. Who would have the resources to 'crack' your code?
Looking at what Al Qaeda does with using hidden codes in religious broadcast to signal attacks one could use a shortwave radio radio show and a bible to create a virtually unbreakable code that would not have to be encrypted. Using the bible verses you could relay information grid cordites and other vital information . Those who are listeners to your show could call in prayers and ask for readings of special verses that would also be a way of communicating information back to the home base. The ability to listen in is second to the ability to understand and put the proper context what you heard . A sample message could be, I would like to send my prayers out to all on the fourm . Ephesians 6:11
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Old 10-28-2010, 12:49 AM
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O_P, Motorola HT750 portables will do what you want, but the "scrambler" chips are not standard. You need a licence (I do not recall the cost per freq) for the freqs you want ot use, then add the chip cost per radio, plus your vox head/earphones.
Stay away from the cheap crap headgear, it will let you down.
I have not dealt with this stuff for a while, but if I recall correctly there are (or where) 2 levels of encription chips available. 6 or 7 years ago the cheaper was $200 per radio, plus about $600 for the radio (depending on how many channels you want), add the best part of $100 each for the headgear. Then pay a Motorola tech to program it up for you, or buy the gear to do that and teach yourself how to do it.
If you buy the radios with hi-cap batteries you should get 16-20 hours of life per charge, but it depends on how much you transmit, which is what really draws the power.
Another thing that you could do is get digital radios, as there are few in use now (but this will change). They are $$$$.
Old 10-28-2010, 06:48 AM
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The "book" encryption method would prob work, but use an old book (published prior to word processing computers) and not a common book (ie the Bible, it's prob been input into data banks already as a code key)... probably better for data transmitted communcation rather than voice....

if your outpost is less than 1/2 mile from base, maybe Frequency Hopping Spread Spectrum eXRS walkie talkies would be helpful...a little higher level of security than just transmitting in the clear....this is a very cheap approach....others here are probably more informed as to this subject than I am ... just my thoughts..
Old 10-28-2010, 10:27 AM
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To generate a one-time pad, they wouldn't used a published book at all. Since that's a finite number and Google has OCR'd many of them at this point.

They would simply generate a whole bunch of random characters. Apparently computer randomizing functions aren't even random enough for that purpose (typically based on seeding the function with a timestamp), so they probably include a whole bunch of other junk interspersed with it, generated from different sources, etc.
Old 10-29-2010, 12:36 AM
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"John has a long moustache..."

The eXRS radios mentioned several times stop virtually everyone from listening in.
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Old 10-29-2010, 12:48 AM
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I found this review on Amazon and it describes an "issue" that the eXRS has because it is a "hopper". As long as you know what the deal is, it is not a problem.

=====

I've tested six of these radios for several hours. The range is quite good for a personal radio, and was better than FRS radios that I've used in the past. However, I found that whenever I changed channels on two of the units (for example, to chat privately), and then changed them back, they would be unable to communicate with the remaining units for some period of time. I also found that if you turned on two units and talked between them, and then turned on a third unit within 20 seconds or so, the third unit would be unable to communicate with the first two.

I exchanged emails with technical support and determined that the problem is caused by a design issue with these units which essentially requires you to wait 30 seconds before transmitting whenever you change channels or when you first turn the unit on. If you don't wait, your unit might become out of sync with the other units, and you won't be able to hear or talk to anyone, even if they are on your channel. You also have to keep the newly turned on unit at least 20-25 feet away from any other units that are already on, or they could become incorrectly synced.

Here's the problem: Each "channel" on this radio actually uses 50 separate frequencies and the radio hops between them whenever it is transmitting or receiving. When you first turn on a radio, or when you change to a new channel, your radio goes to the Frequency #1 for that channel and waits there until one of two things happen: Either you push the transmit button, or the radio picks up someone else doing so. The moment that happens, the radios begins hopping through the 50 frequences in a sequence that is defined by the channel number you selected. When you stop talking, the radio continues through all 50 frequencies, and then returns to Frequency #1 to wait for another transmission. These radios take about 20 seconds to hop through all 50 frequencies.

As long as both radios begin hopping at the same time, everything works great. But, if one radio transmits within 20 seconds before another is turned on, the two will be out of sync.

Here's an example: If you turn both Radio #1 and #2 on at the same time, and then start transmitting, Radio #1 will transmit, Radio #2 will receive, and they will both begin hopping together, through frequencies #2 to #50. All is well.

If you then turn on Radio #3 while Radio #1 and #2 are doing their hopping, it will be on frequency #1. It will wait at Frequency #1 until either you transmit or it hears someone else transmitting on Frequency #1. It cannot hear radios #1 and #2 because they aren't on frequency #1. They are hopping through frequencies #2-50 and will be doing so for roughly 20 seconds before they return back to frequency #1. If you wait for radio #1 and #2 to get back to Frequency #1 (which can take as long as 20 seconds), then Radio #3 will join the hopping and Radio #3 can hear Radio #1 and #2.

However, if you transmit on Radio #3 before Radios #1 and #2 return to Frequency #1, Radio #3 will begin hopping, but it will be out of sync with Radio #1 and #2. Thus, Radio #3 might be hopping past frequency #13, but Radios #1 and #2 may be hopping past frequency #42. They won't be able to talk to one another.

So, if you have transmitted on Radio #3, you'll have to stop transmitting on Radio #3, and wait 20 seconds for it to get back to Frequency #1 (where it will stop) or turn the radio off and then back on (so it will start on frequency #1). Then you'll have to wait another 15-20 seconds for radio #1 and #2 to get back to frequency #1 as well. Then all the radios will be in sync again.

To complicate matters just a little further, if Radio #2 is receiving a transmission and Radio #3 changes to the same channel as Radio #2, Radio #2 will emit some kind of spurious emissions which can confuse Radio #3 and cause it to begin hopping even though it is not in sync. This will cause a choppy/staticy signal on Radio #3, and will cause the radio to begin hopping even though it is not in sync. The signal will come and go.

To solve this problem, you can move Radio #3 away from any radio receiving on the same channel (at least 25 feet) and then wait for it to sync with all of the other radios.

The same problem can occur if you turn all three radios on at the same time in close proximity, and then transmit on one. One of the two that is receiving can send out a spurious emission causing the third to be out of sync.

These problems are relatively easy to overcome if you know about the issues and you either never change the channels or always wait 20-30 seconds after doing so. But, if you are using three or more, you probably want to use the private channel feature, which allows two radios to go off on their own. If they do so, when they come back to the group channel, they may be out of sync with the radios that did not go to a private chat, if any of them have transmitted within 20 second before the private chatters came back to the group channel.

Even worse, the private chatters will probably be in sync with each other, and so they'll be able to talk on the group channel, but they won't be heard by anyone else and they won't hear anyone else, until they stop and wait 30 or so seconds...


=====

If the security of the comm is important, this is a small thing to deal with for such a reasonable price.
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