I've been goofing around with APRS on my 5 watt mobile radio, and to my astonishment I'm pinging portals that are 400 miles away, with a LOT of mountains between us.

Curious if anyone is using it as a primary or backup tracker in their airplane? I can see pros and cons to it, but haven't goofed around with it enough to have much of an idea how well it would work for that function.

I used it when I was paragliding with a handheld as a way for my girlfriend to find my body, and to monitor weather on the California coast with a weather station. My region was fairly static, but it worked very well.

My wife's uncle has a 50W portable with a belly antenna installed in his Musketeer in Colorado. His flying is all east of the Rockies, and he has outstanding APRS coverage. His wife uses it as primary info to check on him. He also does DX with it. You can reach out a long ways at 10K.

I use it, primarily thru the cell network, but I also bring my 5w handheld. I need to add an external antenna for that. I have it setup for smart tracking, works really well.

Flight tracking is perfect for APRS. I've used it for balloon tracking and it has amazing reach. There are few shadows of reasonable coverage anywhere outside of the lonliest areas of the desert west.

Ok, I give up. What is APRS?

Kurt

G44 wrote:Ok, I give up. What is APRS?

Kurt

Same here.

Still digesting this: https://en.m.wikipedia.org/wiki/Automat ... ing_System

CamTom12 wrote:

G44 wrote:Ok, I give up. What is APRS?

Kurt

Same here.

Still digesting this: https://en.m.wikipedia.org/wiki/Automat ... ing_System

I'm not the best person to answer that...I've been phucking around with it for a couple months and I'm still not sure what's happening. All I can say for sure is that there's no subscription fee, it will ping every minute or less, it seems to be astoundingly efficient from a radio-communication point of view, and if it works properly you can be tracked on a map...

It seems to be a standard for maritime vessel tracking, for whatever that's worth.

I was sort of hoping someone who really understands the system would pipe in.

APRS is a local ad hoc messaging network of stations that can be used to send and receive messages. Anyone can set up a repeater station, and anyone can send short messages on the ad hoc network. Once you send a message, the message is received and checked if it has been received before and how many "hops" is has undergone before reaching the repeater, and whether it was sent too long ago. Otherwise, it is re-broadcast and picked up by adjacent repeaters, and again, etc.

Eventually it may be picked up by a repeater that will message a larger network (like the internet).

It is like a party line in that any interested stranger can see the messages.

It is not bandwidth efficient, and DDOS consists of sending rapid messages (1hz kills 3-5% of the bandwidth). So it is important to is wisely and as sparingly as practical.

In short, it's like a barely more sophisticated version of "telephone" you might have played as a kid. But it works really well in a lot of applications.

Other similar ad hoc network examples are FLARM, TCAS, and ADS-b. They are all easy and cheap to implement, and the only reason for high costs on the latter two examples are....well, it would sound cynical to say why.

You can get set up with a Ben Franklin with APRS pretty easily.

I used APRS with a 2m/440mhz rig and it worked really well in most phases of flight until you drop low into a canyon which is to be expected. Surprising how far you can reach with a few watts of tx power.


Sent from my iPhone using Tapatalk

I've played with it. I have this setup:

https://www.byonics.com/rtg
and
https://www.yaesu.com/indexVS.cfm?cmd=D ... 288EF4C787

I find that there are enough digipeaters and igates around to relay my position to the internet if I'm in the matsu or anchorage bowl, but once I pass beyond that, it's pretty useless. It's probably a totally different experience in the lower-48.

A few years ago I played with the other side of the system. I built a tnc-x and connected to a linux server running aprx, then later made the setup a bit simpler by running my digipeater on a raspberry pi using a tnc-pi card. I figured I should be part of the network that relays to the internet if I'm going to be using it.

I eventually abandoned it because I moved and life had other priorities, and because my garmin in-reach does the same thing anywhere on the planet (but only for people I give access to), but I'll probably go back to it at some point when I'm in the lower-48 as I suspect you would get very good coverage most of the time.

Works well here in the Northeast. I like the feature of the website I use (APRS.FI) that records the tracks and stores them for several years and can be recalled and re-played. My set up is a Byonics Tiny2 with their GPS into a 25 watt yeasu radio mounted under the passenger seat. Unit comes on with the master avionics switch, so I don't have to play with it. Antenna is hidden inside the vertical stab where I installed it during construction of the kit. Here is a typical flight: https://aprs.fi/#!call=a%2FN1AGV-7&time ... tail=86400

pouellette wrote:Works well here in the Northeast. I like the feature of the website I use (APRS.FI) that records the tracks and stores them for several years and can be recalled and re-played. My set up is a Byonics Tiny2 with their GPS into a 25 watt yeasu radio mounted under the passenger seat. Unit comes on with the master avionics switch, so I don't have to play with it. Antenna is hidden inside the vertical stab where I installed it during construction of the kit. Here is a typical flight: https://aprs.fi/#!call=a%2FN1AGV-7&time ... tail=86400

Is there a way to filter you from the others?

I was thinking about this thread last night and wanted to write more about the pros/cons of APRS and exactly how it works so that a laydude or laychick can be more informed as to what it is and how it works.

Simply put, a APRS is a voluntary system put together by amateur radio operators (HAMS) that uses a digital encoding device (TNC) to broadcast information over the radio.

Think of it like an old school dial-up modem, or fax machine that encodes digital information into sound frequencies, but instead of using a phone line to transmit that encoded information, it uses a radio. This is why an APRS signal sounds like a modem or fax machine.

The data transmissions are typically very short, only lasting a second or two, and can be picked up with anyone with a radio and another TNC to decode the information.

APRS is typically used to transmit GPS and weather information, and the receiving end typically consumes that data, rebroadcasts it to extend range (like a repeater), or is relayed to the Internet. The repeater station is called a digipeater, and the station that relays to the internet is called an I-gate.

So, if I have an APRS transmitter in my aircraft that periodically transmits it's location and speed, then any digipeater or I-gate can take that information and relay it to other stations and/or the internet, allowing others to use aprs.fi or some other website to track my movements.

There was a recent thread discussing the merits of using an in-reach in place of a PLB (I say in-reach because I think the SPOT is unreliable) so I suppose much of the same arguments apply to APRS, but instead of trusting a private sector satellite network, you are trusting that there is a volunteer i-gate in range.

Also consider, that a spot/in-reach/PLB uses satellites which are above while an I-gate is on the ground, so while APRS might work fantastic at 10k feet, it almost certainly won't on the ground unless you are within a few miles of an i-gate.

I have all three, 406 beacon in the aircraft, in-reach on my person, and have used APRS a bit, but would not trust the APRS solution as a life-line or even secondary life-line as it would be useless beyond last known trajectory.

So, if you want a free tracker that works most of the time, want to get your HAM ticket, and are interested in playing with radios and electronics, APRS is great, but for your average user that just wants a tracker with life-line backup, the in-reach is absolutely worth the cost, and it's simple.

Another factor is the privacy. In the same way that you shouldn't post your vacation pictures on social media (if you have it) until you get back least someone help themselves to your belongings while you are out of town, I don't think broadcasting my position all of the time is wise, which is why my friends and family can see my in-reach map, but it's password protected to keep others out.

In short, APRS is interesting, but I think the reliability and privacy issues prevent it from being a useful aircraft tracker.

CamTom12 wrote:Is there a way to filter you from the others?

If you go to APRS.FI and enter my callsign N1AGV-7 in the search box, you should see my track...

akschu wrote:...
In short, APRS is interesting, but I think the reliability and privacy issues prevent it from being a useful aircraft tracker.

I tend to agree, though I can see it being handy for some people, some places. I think the most interesting thing about the technology is how far the radio signal will reach. I'm in SW Montana, and my 5 watt hand-held radio will pick up stations in Canada. I'm not entirely sure how that works...maybe it's being relayed over and over until it gets to me?

As a side note, while I understand the argument that an amateur radio license is required to use APRS because it operates on a frequency within the amateur band, the vast majority of the traffic I see is not associated with a amateur call sign.

Hammer wrote:

akschu wrote:...
In short, APRS is interesting, but I think the reliability and privacy issues prevent it from being a useful aircraft tracker.

I tend to agree, though I can see it being handy for some people, some places. I think the most interesting thing about the technology is how far the radio signal will reach. I'm in SW Montana, and my 5 watt hand-held radio will pick up stations in Canada. I'm not entirely sure how that works...maybe it's being relayed over and over until it gets to me?

As a side note, while I understand the argument that an amateur radio license is required to use APRS because it operates on a frequency within the amateur band, the vast majority of the traffic I see is not associated with a amateur call sign.

Every transmission on the APRS network should have a call sign, it's part of the protocol. Here is an example APRS transmission:

N1AGV-7>APT311,KB1AEV-15*,WIDE2-1,qAR,N3LEE-4:!4209.06N/07243.04W'014/011/A=000295

As you can see the very first part is the call sign-7 which means N1AGV's 7th APRS device.

As for the distance, there are pretty much two factors:

1. Digipeaters

APRS digipeaters rebroadcast the transmission immediately after they receive it. If two digipeaters are nearby they may both TX at the same time and cancel each other out, but for more distant receivers, it can travel around obstacles or around the curvature of the earth. Something like this:

APRS TX <-> digipeater A which immediate rebroadcasts <-> digipeater B which immediately rebroadcasts <-> I gate.

Now lets suppose there is earth between digipeater the APRS tx and the I-gate, it gets through anyway because of the digipeaters.

But lets suppose that the APRS TX is between the digipeaters but still didn't have an RF path to the I-gate, then when it broadcasts both digipeaters would hear it, then they would both rebroadcast at the same time and basically null each other out for receivers in ear shot of both, but the I-gate will still hear Digipeater B but not digipeater A.

This system works to get around stuff, but with enough APRS traffic, it gets super noisy and because nothing checks to see if another APRS tracker isn't already transmitting, you can have a pretty high packet loss in busy areas.

2. Altitude.

Take a look at this calculator:
http://www.calculatoredge.com/electroni ... fsight.htm

If I have an antenna at 10 feet, then I only have 3 miles of range before the curvature of the earth is in the way. With an antenna at 1000 feet, it's 45 miles. This means that you are pretty much line of sight to all of other transmitters.

It doesn't matter how many watts your radio has if in RX mode, what matters there is rx sensitivity, and any gain you have on your radio. Given the remote end with 5 watts of power and any reasonable amount of RX sensitivity and a 0 gain antenna, you would be able to pick up signals very far away. 5 watts is plenty enough power to talk to a satellite depending on frequency.

My in-reach is only 1.6 watts of power, but it operates at 1.6ghz.

Anyway, what I said before, I think it will have amazing range while in the air, but on the ground it will depend greatly on what i-gates are in the area.

schu

FWIW I've been using APRS for 10 years. Reasonably reliable in most places. I had good coverage between Reno and Smithers BC headed north a few years ago. Also reasonable coverage flying in central Yukon. Works well in most places in the conterminous US unless you are remote and low altitude. On the other side of the coin, flying in the central valley of CA it can jam up the network somewhat. That's because from an airplane at altitude, the signal reaches a LOT of repeaters. I tend to turn it off in those areas. Has been good for the wife wondering where I was and whether I was alive. Nowadays, using a Garmin Inreach can serve the same purpose with better reliability, but you have to push the button every time you want to send a message. And Garmin requires a subscription, APRS is free. Garmin = no license; APRS = ham license.

GregA wrote:FWIW I've been using APRS for 10 years. Reasonably reliable in most places. I had good coverage between Reno and Smithers BC headed north a few years ago. Also reasonable coverage flying in central Yukon. Works well in most places in the conterminous US unless you are remote and low altitude. On the other side of the coin, flying in the central valley of CA it can jam up the network somewhat. That's because from an airplane at altitude, the signal reaches a LOT of repeaters. I tend to turn it off in those areas. Has been good for the wife wondering where I was and whether I was alive. Nowadays, using a Garmin Inreach can serve the same purpose with better reliability, but you have to push the button every time you want to send a message. And Garmin requires a subscription, APRS is free. Garmin = no license; APRS = ham license.

Seems to me that you could just limit your radio to 1/2 watt in CA and still broadcast and not jam everything up.

Another interesting note is that ads-b isn't entirely different than APRS in its implementation. It will struggle when there are lots and lots of targets.

N1AGV-7>APT311,KB1AEV-15*,WIDE2-1,qAR,N3LEE-4:!4209.06N/07243.04W'014/011/A=000295

As you can see the very first part is the call sign-7 which means N1AGV's 7th APRS device

Actually the -7 after my call sign puts the airplane symbol on the map. If I were a car, I would change it to -9. Different symbols are available for any vehicle, including the space station in orbit.
http://www.aprs.org/symbols.html

pouellette wrote:

N1AGV-7>APT311,KB1AEV-15*,WIDE2-1,qAR,N3LEE-4:!4209.06N/07243.04W'014/011/A=000295

As you can see the very first part is the call sign-7 which means N1AGV's 7th APRS device

Actually the -7 after my call sign puts the airplane symbol on the map. If I were a car, I would change it to -9. Different symbols are available for any vehicle, including the space station in orbit.
http://www.aprs.org/symbols.html

opps, got that wrong. Thanks for the correction.