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Thread: APRS Thread.

  1. #1
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    APRS Thread.

    Probably some readers wonder what APRS is.
    I will try to describe it in several posts here, hopefully others will post as well.
    APRS stands for Automatic Packet Reporting System.
    Developed by Bob Bruninga, a Ham that is an engineer at the US Naval Academy. Its about 25 years old.
    I think his original intent was really for APRS to be used in a vehicle with a computer with a display and the radio stuff that we are all discussing.
    I have run APRS in the car with a computer, and it is pretty useful for keeping track of other stations near you.
    When I first used it we used it as a resource management tool to see where our Search and Rescue units were.
    But for me now, having to play around with a computer in the car just to see other stations just isn't that useful.
    But I have run a "tracker" for many YEARS.
    A tracker is a mobile unit that doesn't have a display.
    You use a basic two meter radio set to 144.39, and a GPS and some sort of ENCODER to put the GPS data in a useful form, AND modulate your radio.
    People started out using just any old Packet Radio Terminal node controller. Known as a TNC.
    The TNC ( or APRS encoder ) is a radio modem.
    It MODulates your transmitter and DEModulates signals from your receiver if it is a real TNC.
    It happens that Packet radio started using 1200 baud AX25 as the standard with which to modulate and demodulate audio on 2 meters.
    So, APRS pretty much stuck with that.
    I use the Byonics TinyTrac III plus, as my encoder, a Garmin 18LVC "hockey puck" type GPS, and a very old 2 watt Icom handheld.
    I think the TT3+ is something like 30 bucks, handheld was 20, and the GPS was about $120.
    Probably cheaper stuff now.
    But I still like the TT3 or now the TT4.
    The TT3 does not DECODE the APRS traffic on the frequency you are using.
    It just monitors for traffic so it is less likely to TX over another station.
    The TT4 actually decodes ( receives ) traffic so you could display the APRS signals on a computer.
    That is why it costs more.
    It is actually easier to modulate packet type signals, than to demodulate.
    So, how is this useful?
    Well, at first, it wasn't that useful.
    You had to be somewhere where someone else was in radio range to "hear" your transmitted packet. The "packet" has your callsign, location, elevation, and speed. Can have some other stuff too.
    Now there are HUNDREDS of digipeaters ( digital repeater ) on high places to receive your "packet" and rebroadcast your location, etc. to people further away.
    Beyond that there are IGATES, that receive that traffic and put it on the internet on Websites that display APRS stations on maps.
    I happen to like the Finnish one called APRS.FI
    So, anybody with internet access can find you at those websites.
    As I said earlier, I use a 2 watt radio, and have driven the lower 48 states several times, and it is rare that I don't have a POSIT ( APRS position ) for more than about 20 miles.
    I too am a simple man. I like a fair haired woman.... And Explosives...

  2. #2
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    When you are out driving around with an APRS station in your veh your system periodically transmits your GPS info.
    Location, speed, elevation, callsign, can add status, an Icon for the map, etc.
    The newer APRS encoders have a feature called "Smartbeconing".
    The earliest APRS stuff was old TNC's or other "radio modems" that were not purpose built for APRS.
    So, we just set the system to send our location at a particular time interval, for example 1 minute.
    Which sounds good, until you get several hundred units in an area covered by a mountain site like Slide.
    If you are moving a 5 mph, what is the need for 1 minute interval?
    And if you are going in a fairly straight line in the middle of the desert even at 70 mph, why send positions every minute?
    That is the value of Smartbeaconing.
    Somebody ( that is brilliant ) came up with "program" that is built into these newer APRS encoders that takes your speed and turning into consideration before determining the transmit interval. Does this automatically, all the time if you use SmartBeaconing as a setting.
    So, if you are crawling along on boulders in your 4X4 your APRS might only send a transmission every few minutes.
    But if you make a sharp turn, or go a little faster, the beaconing sends an immediate position.
    So, you can have the best of both without having to change the programming of your APRS system.
    This is more valuable that you might think.
    Because if we all were transmitting at 30 second or even 1 min intervals all the time, there would not be enough "airtime" for us all to get thru.
    No need to send a competing transmission on your veh if you are parked at a traffic light, or idling somewhere looking at a map or picking a route thru a boulder field.
    I too am a simple man. I like a fair haired woman.... And Explosives...

  3. #3
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    So, now what happens when your system sends a "POSIT".
    With most "trackers" ( meaning one that sends postion, but doesn't receive and decode them ) your GPS gets your location, speed etc.
    The GPS is connected to the APRS encoder, the encoder takes that GPS info, looks at where you are now, VS. where you were at the last POSIT if you moved enough, the encoder keys your radio, and sends the new position.
    Built into the data that gets transmitted is a "field" for just how many times to relay YOUR transmission.
    This is best filled with WIDE2-2.
    What happens is with these weird numbers the "digipeaters" will relay ( repeat ) your transmission.
    Hopefully / usually at MUCH higher power and from a better location.
    I can't recall the EXACT specifics, but here is generally how this works:
    You are in the middle of nowhere, you transmit with WIDE2-2 the first digipeater that "hears" you receives your data, stores it for a second or two.
    Then it relays ( repeats ) your transmitted data, BUT the digipeater decrements the WIDE value by one.
    So, another group of mountaintop digipeaters will either relay it once more, or it will stop.
    If you use WIDE numbers that are too high, what happens is EVERY mountain that hears you either direct, or thru other digipeaters will RELAY you over, and over and over. Sometimes DOZENS of unneeded transmissions.
    So, around here for example, if you are RELAYed at Slide mountain it might get relayed to moutaintops all thru CA and OR, which just uses up airtime.
    Once you are RELAYed a "hop" or two, you likely are on the internet.
    Now for you guys that go to REALLY remote areas, increasing the WIDE numbers MAY help.
    But ONLY if there is a simple digipeater to go thru, that will relay you to a second digipeater, that relays you to an IGATE digipeater.
    But if there is no "extra" fill in digipeaters, it is just a waste of transmit time.
    I can really see a value in having some people using TT4's or other APRS encoders that can digipeat from your mobile.
    But they are a pain to get set up.
    I too am a simple man. I like a fair haired woman.... And Explosives...

  4. #4
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    Most of the simple APRS encoders transmit and just hope the digipeaters and ultimately an IGATE received the packet of data.
    There is no error correction. The transmission was sent, lets hope someone got it.
    A FULL APRS station sends a transmission ( a packet ) a digipeater relays it, your station hears what was sent, and if it is wrong, it sends it again until it is relayed correctly.
    Not really necessary, because if a packet is sent, and there is "damage" to the data, then the whole packet is "discarded" and a digipeater won't RELAY it at all.
    It is REALLY important to get YOUR transmitter matched up with your APRS encoder.
    REALLY IMPORTANT.
    REALLY, REALLY REALLY IMPORTANT.
    Just because you hear it transmit that loud BRAAAP sound with another receiver nearby, does not mean the data can be read 100 miles away at a mountaintop digipeater.
    WARNING technical discussion ahead!!!
    When you send data over a radio, the audio is shifted between two ( or more ) freqencies. Audio Frequency Shift Keying. AFSK.
    APRS uses AX25 as the protocol.
    Which specifies the two tones sent as 1200 hz, and 2200 hz. and that the speed is 1200 baud.
    You won't have to worry about that part. The encoder or TNC ( radio modem ) takes good care of all that, unless they are damaged.
    You should worry about the audio deviation. ( How LOUD the two tones are sent )
    You should check the "twist" ( difference in loudness of between the two tones )
    And you should check that the radio is keyed a couple hundred milliseconds before data is sent to the radio.
    What?
    Why do you have to do all that?
    It isn't that tough.
    See next...
    I too am a simple man. I like a fair haired woman.... And Explosives...

  5. #5
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    So why do you have to do those few things, well you want your APRS packets to be the BEST POSSIBLE so that they can be "read" and RELAYed at the greatest possible distance.
    Two way FM radio audio standards call for 6 decibels of PRE-EMPHASIS per octave.
    What the heck does that mean?
    More technical BS.....
    When an FM radio transmits something, the low freq parts of our voice get thru better than the highs.
    So ALL our radios bump up the level of the highs in our voice audio at a ratio of 6 dB per octave.
    And ALL or radios receivers bump that audio back back down in a circuit called de-emphasis then it comes out the speaker sounding normal.
    1200 hz and 2200 hz are an octave apart.
    So, the 2200 must be sent "louder" by that 6 dB per octave, or it won't decode at the other end except under really good conditions ( close ).
    And if the two tones together are too loud ( about 2.8 khz deviation ) you also won't decode as well.
    Last, it takes your radio some amount of time to "change" from receiving to transmitting.
    Then it takes the circuits just a few more milliseconds for your transmitter to get up to whatever its TX power is.
    Say you have a 40 watt radio.
    Key the PTT on the mic, and in 20 to 50 milliseconds the circuits likely have "changed" from receiving to transmitting.
    The synthesizer has "locked up" at the frequency you want to transmit on, and the PA is starting to go from zero watts out, building up to 40 watts.
    What happens if you send that packet audio to the transmitter when it is still only up to a watt or two?
    You can be heard very nearby, and maybe even 10 miles. But not at 50 miles. And OFTEN if that audio is sent too early, you just get splatter. ( garbage )
    Every transmitter has some delay.
    Some newer radios MADE for packet will change from RX to full power TX in 50 milliseconds.
    But most are more like 100 to 300 ms.
    Old ICOM 2AT's ( what I use ) need about 200 ms.
    This is a setting you choose when programming your APRS encoder.
    You don't want to set it too long because YOU WILL get interference to your voice radio. You want to keep those packets short to minimize the interference.
    AND the longer your transmission the less air time the APRS frequency has for everyone to get in.
    And you will be sending a carrier with MARK or SPACE ( 1200 hz or 2200 hz) during part of that time. The longer your transmission, the more likely some of the packet can get damaged ( corrupted data ) and if ANY of the packet is damage, it is discarded...
    As for the Pre-Emphasis question, read the info on your APRS encoder. It will tell you what setting or jumper to use to either use or bypass emphasis.
    Choose the correct setting.
    Unless you are using a radio MADE for PACKET and APRS, your mic circuit WILL have pre-emphasis.
    Just do a quick read of your equipment, and you will get it right.
    Normal setups you will be using pre-emphasis for transmit.
    And using de-emhasis for the few that might be using receive.
    Last, setting the TX deviation, it is better to be WAY to low ( softer, not louder ) that to be over deviated.
    Even listening to other people on the air ( hopefully theirs are working right ) and compare yours to that.
    If in doubt, set yours to be a little softer.
    If you know someone with a radio service monitor, it can be set with real precision.
    That it the best way.
    I too am a simple man. I like a fair haired woman.... And Explosives...

  6. #6
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    I know this is a LOT of info to digest.
    But, read thru it once, and you will have enough info to get started.
    Don't be afraid to try it.
    Use the default settings in most APRS hardware manuals, and you have a VERY good chance to have it work.
    If it is not working or not working optimally, this info should give you ideas on what to check for.
    And when or if you go looking for more info, maybe some of the cryptic jargon will make some sense.
    Start with defaults for timing, etc.
    Listen to your transmitter on a second radio.
    Hopefully you will hear other traffic on 144.39 and compare your transmission to that traffic.
    Set the TX audio level out to match that as close as you can.
    If your packets are being decoded by a digipeater, you should hear a RELAY of your packet almost immediately after you transmit.
    Basically, you transmit, and the digipeaters REPEAT it.
    Go to APRS.FI and see if your POSIT can be found on the map.
    I too am a simple man. I like a fair haired woman.... And Explosives...

  7. #7
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    wow Steve... Do your fingers hurt? That is one hell of a post...

    Maybe we can remove liefs post from the middle of Steves and re post it after all that to keep it as one good writeup...
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    Quote Originally Posted by PhantomRage View Post
    wow Steve... Do your fingers hurt? That is one hell of a post...

    Maybe we can remove liefs post from the middle of Steves and re post it after all that to keep it as one good writeup...
    If Lief is okay with that I will do it. I agree it would be nice if it was one continuous series of post.

    Since there is a lot of interest in APRS I'll start a new FAQ just for APRS threads.
    75 FJ40 w/stuff; 98 UZJ100 kinda stock; 1984 FJ60
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    Quote Originally Posted by rusty_tlc View Post
    If Lief is okay with that I will do it. I agree it would be nice if it was one continuous series of post.

    Since there is a lot of interest in APRS I'll start a new FAQ just for APRS threads.
    I don't think he knew that steve was going to post more.. But yeah, I agree.

    and if it does get done, feel free to kill my post in the thread as well, since it really gives no real input
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    Quote Originally Posted by PhantomRage View Post
    I don't think he knew that steve was going to post more.. But yeah, I agree.

    and if it does get done, feel free to kill my post in the thread as well, since it really gives no real input

    You are right, I was thinking he was making a discussion tread...
    Last edited by leifnv; February 3rd, 2012 at 09:30 PM.

    It is perfectly legal to be stupid....
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    ************************************************** ************************************************** ****
    I am NOT a doctor, police officer, FBI agent, ambulance tech, or Part 90 dispatcher.
    I am an amateur radio operator, in what still is, at least somewhat, a quasi-technical hobby.
    I am NOT a DHS employee, and I don't work for FEMA.
    I am a freaking bus driver, yapping on the radio, playing with antennas and having FUN


  11. #11
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    Quote Originally Posted by rusty_tlc View Post
    If Lief is okay with that I will do it. I agree it would be nice if it was one continuous series of post.

    I beat you to it...

    Just for the hell of it, my name is spelled L E I F

    It is perfectly legal to be stupid....
    STOP
    abusing the privilege.....
    ************************************************** ************************************************** ****
    I am NOT a doctor, police officer, FBI agent, ambulance tech, or Part 90 dispatcher.
    I am an amateur radio operator, in what still is, at least somewhat, a quasi-technical hobby.
    I am NOT a DHS employee, and I don't work for FEMA.
    I am a freaking bus driver, yapping on the radio, playing with antennas and having FUN


  12. #12
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    Quote Originally Posted by leifnv View Post
    You are right, I was thinking he was making a discussion tread...
    We'll leave the thread open so people can ask questions and discuss but it makes a better tech thread with the initial post in a conductive string.
    75 FJ40 w/stuff; 98 UZJ100 kinda stock; 1984 FJ60
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    Wow, thanks Steve.
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    I think you have the right idea in theory, but you missed the boat completely as to it's proper application.
    In order to legally use Packet - you first have to have a amateur radio license of a Technician Class or higher - due to the fact that your radio is going to broadcast your call sign and your position.

    Packet Radio was never designed to be used as a lOJAC or a GPS transmitter.
    It just so happened that when he designed its use - it was incorporated into the system.
    Packet is a / um - how do I put this, a very primitive form of the internet.
    Anyone with a license, a TNC, A computer, A transmitter, and a keyboard, can enter messages and send / forward and receive information.
    Because all of the transmitters involved are amateur radio transmitters, using packet frequencies, the information that is stored and received and sent is sent to either all the receivers in the area or maybe with a more advanced system - just to the receiver you wish to communicate with.
    As you are traveling, your receiver tells all the other receivers - here I am.
    It can also tell them which frequency you are monitoring right now, or even if you are scanning.
    If by chance - you are talking to someone else who is also using APRS - it can tell others that your signals are active and which repeater you are using.
    If you are traveling in the same direction, and you fall out of one repeater, and you are carrying on a conversation, it can switch you to a different repeater and you wouldn't even know that the hand shake had taken place - much like your cell phone does in your vehicle.
    If your club has a scheduled meeting time, you can post it and when people are in the area, it can display the local news - such as club meetings, repeater frequencies and PL's, things the other mobiles in your area are doing etc.
    Considering that it is FREE To the user, as long as you have a amateur radio license and the proper equipment.
    And considering that it has been around for 25 years - and texting on cell phones has not been around all that long.
    It is actually a more developed / advanced form of communications - for the general public as opposed to a cell phone which only sends communications between point A - your cell phone and point B the person who's telephone number you dialed..
    The other thing is - if there was any sort of natural disaster or crisis, you can send real time data - such as a report which would give all the names of all the people staying in a emergency shelter and could send reports such as needed medications for that shelter that needed to be delivered. Amateur radio is a very advanced form of communications - not like some idiots that we think of that just sits and shouts into microphones like the cb radio people of the 1970's.

    The other thing that most people do not realize is that Amateur Radio works when all other forms of communications fails.
    Let me rephrase that please - cell towers and phone systems are reliable - as long as you have a connection and as long as you have power. Remove either one and you have no phone system.
    Fiber optic cable is a wonderful thing - when it works.
    When someone JCB's the line - you have no working phone or internet.

    Some amateur radio repeaters are built with battery back up - as does most cell towers of any proportion in any major service area.
    Amateur radio repeaters can also be ran off generator power, a automotive battery, or even solar power.
    There are solar power amateur radio repeaters in this country.

    Because APRS does not rely on any type of backbone - it can run independent of the internet. ( store and forward )
    Its just a shame that out of the 700,000 advertised licenses the ARRL claims it has in the FCC data base, there is only about 100,000 active amateur radio operators in the USA and that most times, most repeaters in most rural areas are completely devoid of any radio traffic due to the fact that the technology has moved on - nobody uses amateur radio anymore.
    And that the only time you hear those 100,000 real hams is when there is field days exercises or some type of contest - where they can get exposure for their endeavors - a certificate, placque or other type of award for your accomplishment.
    Last edited by 1964 Jeep; March 9th, 2012 at 06:06 AM.

  15. #15
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    Not sure if this fit here, but ZI will take my chances.
    I found this on another board, and liked it and wanted to share.


    APRS with just an Android phone and an HT that supports VOX

    http://www.4x4ham.com/content.php?24...t-supports-VOX

    It is perfectly legal to be stupid....
    STOP
    abusing the privilege.....
    ************************************************** ************************************************** ****
    I am NOT a doctor, police officer, FBI agent, ambulance tech, or Part 90 dispatcher.
    I am an amateur radio operator, in what still is, at least somewhat, a quasi-technical hobby.
    I am NOT a DHS employee, and I don't work for FEMA.
    I am a freaking bus driver, yapping on the radio, playing with antennas and having FUN


  16. #16
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    Quote Originally Posted by leifnv View Post
    Not sure if this fit here, but ZI will take my chances.
    I found this on another board, and liked it and wanted to share.


    APRS with just an Android phone and an HT that supports VOX

    http://www.4x4ham.com/content.php?24...t-supports-VOX
    I think Chrisalready posted that here---->>>>http://www.reno4x4.com/forum/showthr...and-useful-app

    Still pretty neat stuff.
    75 FJ40 w/stuff; 98 UZJ100 kinda stock; 1984 FJ60
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  17. #17
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    Quote Originally Posted by rusty_tlc View Post
    I think Chrisalready posted that here---->>>>http://www.reno4x4.com/forum/showthr...and-useful-app

    Still pretty neat stuff.
    Yes, the app has been posted before... But it's still under heavy development, and support for going RF instead of APRS-IS is pretty new; I think the TNC support was thrown in late last year, and this is the first I had read about running it through the "Sound card." I'm a bit curious about other keying options though... I'm not VOX's biggest fan, and having a more software controlled keying mechanism would be a plus. I MIGHT get a Blutooth to Serial adapter in the near future and try it all with a TT4...

  18. #18
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    In addition to the aforementioned Android solutions, it might be worth pointing out the AVMap G6APRS, a dedicated navigational GPS unit with APRS capabilities built in. Still needs a TNC, but it's often paired with either a TT4 or a Kenwood TH-72 or a TM-D710 with great results. If you go the TT4 route, it can even do messaging. You can find it on HRO.

    I only mention it here because they are actively working to add in some 4x4 functions, including some features from the G6 FarmNavigator. I'm not sure what those features are going to be, but it's going to be interesting to watch. On a similar 4x4 rant, I have recently downloaded all (Well, most...) of the US Topo Maps for the nation from libremap.org, and converted them to a Google Earth and G6 compatible KMZ format, and am hosting them at KD7KUJ.US.

    I haven't received my G6 yet, but it's in the mail heading this direction. Once I have it, I might be able to demonstrate it when on trail rides

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