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Packet radio

Discussion in 'Survival Communications' started by ghrit, Mar 7, 2014.

  1. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Just last week, the club had a guy in to make a presentation on packet type comms. His emphasis was on PSK 31 as an example of the several (if not many) protocols for what seems to be very narrow band radio use (meaning taking up just a few hertz of bandwidth.) From a purely personal standpoint, packet radio is one of the peripheral things that got me interested in hamming, since I have relatives that use it. I still do not have all the equipment needed to go PSK of any flavor, but am getting more interested after seeing some of the capability in the mode.

    So, the question is whether it makes sense to think in monkey net terms. How adaptable is it to using one pad? Is one pad even needed with the very narrow and short messages given the ability to slither around on frequencies? Any other considerations or concerns?
  2. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Yep, PSK was NOT one of the Protocols I had in mind when I wrote the MonkeyNet White Paper, as it wasn't really common at that time. I was more thinking of HF Packet, HF Pactor1, or standard RTTY. All of these can be done with the OLDer Technology of Hardware Modems, which are "dime a dozen" these days. PSK31 and its Fellow Travelers have a number of advantages over the more traditional Digital Modes, the most significant is that that it requires much less RF Power and the Receive SNR can be significantly lower for full 100% copy. It is a bit slower, but if we are reduced to MonkeyNet for our ONLY link, and HF as out only Physical Link, Slow is the least of our worries.
  3. Snake_Doctor

    Snake_Doctor Call me Snake...

    I didn't understand a word either one of you said. but now i'm curious, are there any micro radios out there that would fit in a PSK?
  4. BTPost

    BTPost Old Fart Snow Monkey Moderator

    PSK is an acronym for Phase Shift Keying and it is a Modulation Protocol for Digital Communication using a Radio Link. If this stuff interests you, you might think about studying up and getting a Ham Radio License. It isn't that hard and there is NO Morse Code Requirement any longer. If 10Year Old Kids can do it, so can you.... and it will open up a whole New world to you.... .....

    Oh, and to answer your Question... Yes... look at the SECURE Phone Blog in the Blog forum at the Bottom of the Main Page.... The i560s are quite small....
  5. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Packet is not pack as in something on your back. In grossly oversimplified terms, packet describes a bundling of code (with a computer) into a packet (or as was described to me one time, a sandwich bag full of 0's and 1's) of data.

    The i560s (and i355s) that BT mentioned are very small radios. Cheap and good for tactical comms.
    BTPost likes this.
  6. Snake_Doctor

    Snake_Doctor Call me Snake...

    Thanks for clearing that up BT and G. I saw PSK and thought Personal Survival Kit. I've never heard of a PSK with a radio in it outside of the military, so it seems like a good idea to me. I have a slim old cell phone in one of my kits. No service on it, but at least I can call 911 to come get me if I'm hurt to bad to walk out on my own.
  7. BTPost

    BTPost Old Fart Snow Monkey Moderator

    You need to go read that SECURE PHONE BLOG.... It will open your eyes...
  8. Most ham operators prefer to talk on the radio, and some old buzzards like me even use Morse code. Those are the most common "modes" for getting a message across on Amateur Radio.

    After WWII, surplus Teletype machines became available to hams, and they used them the same way the military had, and often with the same (surplus) equipment. The big problem with Teletypes on radio is that the signals would get scrambled a lot, due to static, signal fading, interference, changing propagation, etc. It "sort of" worked, but mostly because English is so redundant that the receiving operators could guess at missing characters or words.

    Starting around the 1970's, hams transitioned away from Teletype machines, and started using computers instead. During that time, the Tucson Amateur Packet Radio (TAPR) organization started making and selling circuit boards for a Terminal Node Controller (TNC) which would do all the processing needed to connect a ham transceiver to a computer, and it was a major improvement over the old Teletype-based networks.

    The TNC's were a quantum leap forward for Amateur digital networks, because they included the same error-correcting method used on the Internet: every time there was information to send, the TNC combined it into a data "packet", which is a digital signal that has both the message being sent, and an electronic checksum which allows the receiving station to automatically check for accurate reception. This is the "Packet" in "packet radio", and over the years, various methods have been developed to pack more data into less radio space, i.e., to take up fewer radio channels for the same data throughput rates.

    PSK is a generic name for some of those ways: they include the original "AX.25", "Pactor", PSK31, and even TCP/IP, just like the Internet. They all have the same feature as the first TNC's did: if a receiving node detects that the "checksum" at the end of a packet doesn't match the data, it rejects the packet and tells the sending station to resend it. This means that error-detection and correction was automated, so that hams could enjoy error-free digital communications without the time-consuming manual tests for transmission accuracy which used to be the norm.

    From a prepper perspective, the key advantage of digital modes is that it allows for electronic messages to be sent between unattended stations, so that the users don't have to spend time waiting for whomever they wish to talk with to answer a radio call. That translates into large savings in time, and we all know that time is our most precious asset.

    As with most technical solutions, there are drawbacks to packet radio, especially for preppers:

    1. It's a lot more complicated and consumes more power than a regular walkie-talkie or other "voice" radio. There's the computer, of course, and also the TNC, and the cables to hook them up, plus batteries.
    2. Most Amateur VHF and UHF repeaters are for voice use, not data, and the few "digipeaters" that can relay traffic in a metro area are often at some distance from the end nodes, so packet operators have to get used to having towers, directional antennas, rotators, amplifiers, and long feedlines.
    3. The bandwidth is very limited.
    • One of the most common modes on the "low bands", (which are the ones where over-the-horizon ("skip") transmision is possible), is PSK31 - and the "31" means "31 baud". That's about the rate I'm typing at right now: in other words, it's limited to the same speed as keyboard chat sessions, much like IM.
    • Most operations using TNC's on VHF or UHF are limited to 1200 baud, which is about 100 Bytes-per-second throughput, so they are only a little faster than the old Teletype machines running at full speed.
    • Some VHF/UHF stations are at 9600 baud, and that's "sort of" usable for Emergency Communications, provided the transmissions are kept short. There are several different, and incompatible, methods for getting this speed, which means you can wind up trying to connect two nodes with incompatible equipment.
    • It's not email, and can't be used for that with any kind of reliability.
    • Packet comms are slow, not only because of the low bandwidths, but also because the hams who use them will be doing other things while their TNC's are receiving messages, and that means that getting an answer to a simple question like "Can I trade you some corn for the drum of Sevin you have?" could take as much as a day.
    In summary: PSK and other packet modes are good for short, low-priority messages, like wives asking who's going to bring coffee to Sunday after-worship, or setting up babysitting for next week's town meeting. They are not a substitute for SMS (text) messages on cellphones, or for telephones, and pretty much any "real time" way to get a message through.


    William Warren
  9. Snake_Doctor

    Snake_Doctor Call me Snake...

    Wow. Very informative. Thank you for taking the time to lay it all out for me, and the time it took for you to type it all. Much appreciated. That would be too much trouble for me to get into. When I say PSK I mean Personal Survival Kit. What I'm interested in is a small radio, the size of a cellphone I can pack into a small belt worn survival kit, and that can be used to call for help if I'm to damaged to walk out of a bad situation. Again I thank you.
  10. Mike

    Mike Ol' Army Sergeant Monkey

    Now you're in MY world. Microwave uses Phase Shift Keying, and Trellis Code Modulation (PSK, TCM). Our newer systems are going up into the 512 and 1024QAM (Quadrature amplitude Modulation) ranges now. What it means is that for a single change in phase and amplitude the modulated input can emulate a signal of 12 - 15 bits of information. This is called bit density. It allows radios to broadcast data in the 300 - 500 Mb/s range, and if you use multiple radios on a single path you can get data rates up over 1Gb. While fiber has virtually no limitations on bandwidth other than switching speed of the laser, it is more expensive to put in due to physical limitations as well as purchasing right of way.

    One thing that would be useful in a SHTF scenario would be a burst transmission radio. It stores the voice data, converts it to digital, then transmits the data at a high rate over a very short broadcast time. It makes signal detection and location very difficult.
    Last edited by a moderator: Mar 11, 2014
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  11. Snake_Doctor

    Snake_Doctor Call me Snake...

    Very interesting, my friend. But how does all this help me find a teeny tiny radio to call for help if I'm busted upin the wilderness and can't walk out under my own power?

    In a SHTF situation I intend to go to my tiny, inconspicuous BOL, maybe taking a woman with me, and just letting it sort itself out. There's no one to talk to on a radio, I have no network or group and do not want one. I intend to live small and draw no attention to myself. If there is trouble I'll do my best to deal with it like I have in various spots around the world.
    Last edited by a moderator: Mar 11, 2014
    Mike likes this.
  12. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    I went with a Buofeng UV-3 for that reason. It is smaller than a pack of playing cards, very light, and recharges on USB power (which my solar charger provides. Mercury #10. 10wt. Duel port) so I need never have dead batteries. Comes with a power pack as well for recharging at night.
    Mike likes this.
  13. Snake_Doctor

    Snake_Doctor Call me Snake...

    Thanks kellory. How much are they and do you have a link to it?
  14. Mike

    Mike Ol' Army Sergeant Monkey

    Probably not at all. :p
  15. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    It doesn't, obviously. The more interesting question is why you want one if you haven't a group or someone else to communicate with while loose in the world. Any of the pocket sized radios will be very limited in range, too. Therefore, of questionable value compared to say a more extensive first aid kit. Now, if you are willing to master the idiotic menus on the Baofeng or Wousan sets, there could be some value if you are in range of a repeater that can boost your signal to some one that might be able to provide assistance. That also assumes that there is a repeater remaining powered up.

    Two things:
    -If/when things go out of round, it's highly unlikely that the requirement for a license to transmit will be enforced.
    -Even if you don't get a license, emergency transmissions are still allowed under current regulations.

    The Baofeng units can be found under 50frns, takes just a bit of looking around. Google is your friend. evilbay features one flavor of them for 40frns.

    Now, we should go back to packet radio rather than packable units, eh? WW's discussion pretty welll explains what packet is all about. I, for one, did not realize the baud rate was so low. Interestingly enough, the ARRL is trying to get the FCC to authorize higher baud rates for some services on the lower bands. I don't have the details handy, and am too lazy to look it up.
    Last edited: Mar 11, 2014
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  16. Snake_Doctor

    Snake_Doctor Call me Snake...

    I had thought a small radio to reach a ranger station or some other form of help. I hadn't realized they were like they cheap 2 ways that you can get at Wal-mart. Guess it's back to carrying a cell phone and hoping for service.
    Last edited by a moderator: Mar 11, 2014
  17. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    The ranger station idea might have merit. You would need to know it if was in range, manned, monitoring the frequency, and so forth.
    BT, he said something, dug it out and vanished the dupe.

    Without a pile of auxilliary gear, those little hand helds are not packet compatible, either.
  18. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Ok, Just a NOTE, here: There are FCC Rules & Regulations for the use of Part90 Frequencies (Public Safety & state, local .GOV) by NonLicensees, in Life or Death Emergency Situations. These are covered in CFR48Part90..... HOWEVER, USFS Ranger Comms and Frequencies are NOT covered by ANY FCC Rules & Regulations, PERIOD. They are part of the Executive Branch of the Federal .GOV and are Regulated by the Office of Science & Technology, under the Oval Office. (Mr. Pres.) Therefor NONE of the Emergency Use Clauses found in the Communications Act of 1934, as Amended, apply to ANY Federal Executive Branch Entity, including .MIL Frequencies. There have been Prosecutions, for such instances, that were egregious enough, to attract the attention of the local US Attorney. .
    Mike likes this.
  19. Snake_Doctor

    Snake_Doctor Call me Snake...

    I'm just looking for a possible lifeline G. Don't want to get technical, just turn it on and make contact and say here's my medical staus and here I
    Mike likes this.
  20. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Rather than USFS Ranger Rick for EMS & SAR you should be looking at the local County Sheriff, as they are the Folk's that have the Job, of dealing with such situations. USFS Deal with Trees & Natural Resources, and their LEO Branch mostly does Tree theft investigation, and are rarely tasked for SAR. That is the Sheriff's Job, and responsibility. ......
    Mike likes this.
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