GPS, APRS, and serial (or how I came to realise that redundancy and data are both good things)

[drew]

So, long story short I've had issues of late with my TeleGPS, various versions of firmware, different computers for AltOS telemetry downlink, old TeleDongles, and the like.

Instead of breaking down the minutiae of that situation for all y'all I figured I'd instead share with you the value adds that I've come to develop for tracking.

Specifically, any AltusMetrum GPS capable device (excluding the TeleMetrum 1.x branch of boards) can support APRS packets ALONGSIDE the AltOS telemetry downlink. I like this for the following reasons.

1) I am already kitted up to handle APRS packets as my Yaesu VX-8GR has this inbuilt
2) having a "redundant" system of position reporting is a value add. IF my telemetry downlink isn't functional I can still find my rocket.
3) If both APRS and Telemetry aren't working then I've got a sure fire TeleGPS issue.
4) If I don't have telemetry functional I can still confirm I've got GPS lock before flight. This is important because even IF the telemetry link isn't working the TeleGPS will log the flight onboard for download post flight.

So I started by configuring my TeleGPS to output APRS packets as it's disabled by default. Below is the relevant config windows from AltOS.


Initially I tested with the APRS format being "compressed" as can be seen above. This does NOT work with the VX-8GR. Like the Kenwood TH-D72 the Yaesu VX-8GR only supports Uncompressed format. The Yaesu FT1DR supports Compressed, so my assumption is that the newer FT2DR also supports that format.

Once I got the APRS format sorted output worked exactly as it does with my BigRedBee GPS trackers from a Yaesu downlink perspective. SWEET.

But one of the issues I've had in the past with my BigRedBee trackers is the logging file being corrupted on board post flight. So ideally I'd like to have my APRS TNC in my Yaesu output the Waypoint NEMA strings from my radio over serial. I've always owned the CT-143 PC Connection Cable for my radio, I bought them both at the same time. So I finally pulled it out of the box!

First off I needed to config my Yaesu to output NEMA strings over serial. Below is the configuration settings that are available.


In my specific case, I configured the following.

STATUS: ON
SPEED: 19200bps (this isn't necessarly required, and I'm sure 9600 and most likely 4800 would both work, but I figure the faster the better)
INPUT: OFF
OUTPUT: WAY.P
WAYPOINT: NEMA9

IIRC there were a couple other options I set, but I don't have the radio in front of me to share them.

So, now that I had my Yaesu configured to output NEMA9 strings over serial I connected up the CT-143 cable to my radio and the other end to my USB to Serial adapter. I then opened up Putty and configured it for the COM port my serial adapter took (in my case COM9) and set my baud rate to 19200. Clicked open, and my NEMA strings started to appear in my console output once every 5 seconds!


Now there's more to do but right now I can take the GPS output via serial, slightly modify it, and drop it directly into Google Maps for a Hybrid overlay of where my rocket is!

Specifically, the serial output is rougly in the following format.
32xx.xx,S,116xx.xx,E

I modify that to the following format in Google Maps
32 xx.xx S 116 xx.xx E

And press search and my GPS tracker location is displayed on my phone in Google Maps! Plus when I'm ready to depart for my recovery I just unplug my Yaesu from the serial port and use the inbuilt APRS TNC to provide me both bearing and distance values of the last packet as it has GPS and calculates where it and the rocket both are. Plus all the serial output modifications I've made should work "out of the box" with my BigRedBee hardware. BONUS!

Next up I plan on investigating YAAC but in the interim I'm quite pleased with the progress I've already made.

[drew]

So I've been meaning to provide an update to this thread. Here we go.

First off, my above TeleGPS Configuration screenshot isn't correct as the APRS Interval(s) value is 0. 0 effectively means it's off. Below is the correct "working" configuration for my VX-8GR. Notice APRS Interval is at 5 seconds and the APRS format is uncompressed.


Next up, below is a screenshot of the YAAC Raw Packet Sniffer AND my TeleGPS App both running simultaneously and both producing GPS location data. And these are two different live location data feeds, one APRS, one Altus Metrum Telemetry. This is what I'm after so to speak. As mentioned, if Altus Telemetry has issues I can always fall back on the APRS location data. Furthermore having APRS working will allow me to use just my VX-8GR for rocket recovery instead of attempting to lug a Teledongle + laptop into a paddock. Sure, I could use AltosDroid but I have the most connectivity issues with that app plus if I'm being honest USB-C doesn't really tickle my fancy. The cable connection is a bit flaky on the phone when compared to MicroUSB that had a more positively retained attachment for OTG dongles.


YAAC is nice and is very easy to setup and configure. That said I'd ideally like to have a satellite or hybrid overlay for my location window (not pictured) and I'm not sure if that's available. You can easily get OpenStreetMap data (less useful) into YAAC as well as topographical data (more useful) but ideally having a satellite image would make recovery more simple. I'll investigate that more soon.

I haven't been able to get altitude data to output over serial. I don't think I'll be able to do that with NMEA. That said I'm going to grab a Mobilinkd and have a play with using APRSDroid + a Baofeng + Mobilinkd to provide a backup APRS receiving capability for the field. That update will take some time though as I ordered a UV-3R from AliExpress and it'll take a month or so to get here given it's free shipping.

[drew]

So I've been meaning to chime in with another update, so here we go. First off, I think it wise to take a step back and look at what I'm actually trying to accomplish. Bear with me, we'll get there in the end.

It's worth mentioning that there are two things that we require to receive and decode APRS data from an APRS capable GPS tracker. First off, we need a radio to receive the Audio Frequency Shift Keying (AFSK) signals being transmitted from the APRS tracker. You might not have heard of AFSK before, but you've most likely heard it before, either on the flight line or an incredibly old dial up modem. Here's an example of a 1200 baud AFSK-modulated signal from Wikipedia.

https://en.wikipedia.org/wiki/File:AFSK_1200_baud.ogg

Next up, we need a Terminal Node Controller, or TNC. Basically the TNC is what translates the AFSK transmission from the tracker into a digital format that we can then read to get our APRS transmitted GPS position data. Inbuilt TNCs are what make high end handheld radios like the Yaesu VX-8GR, FT2DR, or the Kenwood TH-D72A able to decode APRS transmissions from our various APRS capable GPS trackers. Obviously those devices are quite expensive and normally run in excess of $500AUD at a minimum. So that's a pretty high bar from a financial perspective. The Mobilinkd I've been looking at recently is a purpose built APRS TNC that leverages serial over Bluetooth to transmit decoded AFSK signals from a tracker over any given frequency to APRSDroid on an Android device. So it sits in between a radio and a Android device and provides TNC functionality in a reasonable package.

But given the relative computing power of PCs, laptops, and even phones and tablets we now have the option of using software based TNCs to do the decoding for us. APRSDroid supports three different methods of APRS transmission mediums.

1) APRS-IS (Internet based APRS) - this doesn't require a radio of any description, you share your APRS data over the Internet. But it requires an Internet connection and isn't really applicable from a rocketry perspective (unless you want to fly your phone).
2) Bluetooth - As mentioned earlier Android phones support serial over Bluetooth connections. This allows a Bluetooth enabled TNC like the Mobilinkd to work with APRSDroid. The TNC receives the AFSK signal from a VOX capable radio over a physical audio cable, decodes it, and transmits the data over Bluetooth which is "seen" as a serial connection from an Android perspective. This would work for us but requires a serial to Bluetooth capable APRS TNC. Good, but not ideal. Also, Also, Apple iOS does not support Serial over Bluetooth.
3) APRSDroid supports direct audio input/output. One of the features of APRSDroid is that it can operate as a software based TNC So basically we need to connect the handheld radio directly to an Android device running APRSDroid with the appropriate audio cable. Remember effectively all we need to do is output the AFSK signal from our handheld radio to the audio jack of the phone.

Big shout out to DaveW6DPS over on TRF for pointing this out. That thread can be found here.

https://www.rocketryforum.com/threads/very-simple-and-inexpensive-way-to-receive-aprs-data.147891/

And the original post from a 4x4 forum in 2012.

http://www.4x4ham.com/showthread.php?2078-APRS-with-just-an-Android-phone-and-an-HT-that-supports-VOX

Finally, here's the page DaveW6DPS wrote up for this use case for rocketry.

https://www.qsl.net/w6dps/APRSDroid.html

So given this I've decided to not buy a Mobilinkd TNC and instead buy a couple of their TNC cables instead. These cables are made to interface with various handheld radios on one side and 3.5mm TRRS connectors on the other side. From my understanding most Android devices that have a headphone/hands free connector port are TRRS connectors (4 pole connector). Probably the easiest way to confirm this is to look at the wired hands free headphone/microphone that came with your phone.

Here's the Baofeng UV-3R cable Mobilinkd sells which shows each side of the cable is a 4 pole connector.


I've also ordered a TNC cable for my Yaesu VX-8GR so I can test on a "good radio" as well as the Baofeng just in case all the ranting about those radios being useless is truly correct. That said the UV-3R is sitting on an average rating of 3.9/5 over 131 reviews over on eham.net so I'm not too sure as to whether they're as bad as the vocal minority make them out to be.

Regardless, the cables and a few 4mm Ferrite Beads are making their way down here as I type this. I suspect I'll get them at the end of the month. Hopefully my UV-3R will show up soon as well. I'll update the thread once I've done some testing.

Thanks for reading.

[drew]

The UV-3R just arrived! Not bad considering I ordered it on Sept 3rd with free shipping.

Man this thing is small!

[drew]

Time for another update. As previously mentioned I received the Baofeng UV-3R some time ago. Last week I also received my cables from Mobilinkd as well as a TeleGPS v2.0. Time for some testing!

First off I connected to the TeleGPS via the AltOS "Configure Altimeter" feature to enable APRS and change my Frequency channel from the default. I also changed the APRS SSID value to 10. I left the Callsign field unchanged though as I thought broadcasting N0CALL would be good for testing purposes to highlight clearly whether or not APRSdroid is working. At this point I must mention that I was quite pleased to see the TeleGPS v2.0 was already running the latest firmware at the time of order, specifically v1.8.6.

Next up I had to give myself a bit of a crash course on the Baofeng UV-3R. It's not the easiest radio to operate but given the $23 USD price tag that's not entirely unexpected. Regardless, getting it up and configured was pretty simple once I wrapped my head around the UI.

To put it simply, it works! Instead of writing out the steps I took in long form here's a quick list of what I did to get everything to work.

On the Baofeng UV-3R
Set Frequency ex 434.550
Set VOX to 7

Connecting the phone and radio
Plug in Mobilinkd radio specific cable to radio and phone

On my phone in APRSdroid
in Preferences, click Connection Preferences
Make sure Connection Logging is enabled
in Connection Protocol, select Audio (AFSK)
Back out to main screen, click "Start Tracking" in the bottom right of the window

Once all that's done all that's required is to power on the GPS Tracker. Assuming it's configured to transmit across the frequency we're listening on (in the example above 434.550 MHz) then as soon as the radio starts receiving AFSK encoded APRS data it will be displayed in APRSdroid in the main tracking window. Once you see your transmitter (in my case N0CALL) then you can click on the entry to open up the log of that transmitter. When you do so you'll see a screen similar to what's below.



As mentioned above by enabling Connection Logging in APRSdroid you can store each packet locally to be reviewed or even shared at a later date. Post test I shared the log file to my Gmail account and in next to no time an email with the APRSdroid log file (aprsdroid-20180930-2011.log) in my inbox. Opening that file in Notepad ++ reveals a full log of all APRS packets I received during the test. Below is an excerpt of that file highlighting GPS lock had been achieved and GPS position and altitude data are being shared.



There are a few things worth mentioning.

1) I suspect this process will be a bit more error prone in terms of output when compared to the Altus Metrum telemetry offering. I also suspect that there might be more error in AFSK decoding over the phone when compared to using an inbuilt TNC. I'll test to confirm or deny this shortly.
2) Unlike the serial output from my Yaesu VX-8GR the altitude data is also being decoded via APRSdroid. That's great news.
3) The APRS SSID value configured on the TeleGPS displays in APRSdroid after the callsign. So N0CALL-10 is due to my callsign being N0CALL and my APRS SSID besing set to 10.

Now that I've got the Baofeng working I'll run the same gamut of tests on my Yaesu VX-8GR. One of the great things about that radio is I can have the above running (Mobilinkd cable + APRSdroid) alongside serial output from the TNC inbuilt in the Yaesu as my audio and data ports are separate. That should allow me to easily confirm if variations in position are due to incorrect AFSK decoding (my expectation) or if the GPS is actually spitting erroneous data as I'll have what should be two sets of identical data (excluding the altitude output of course).

Next up, Garmin, OpenStreetMap, and APRSdroid with OSM integration. We're getting there folks...

[Sirbrad]

Time for another update. As previously mentioned I received the Baofeng UV-3R some time ago. Last week I also received my cables from Mobilinkd as well as a TeleGPS v2.0. Time for some testing!

First off I connected to the TeleGPS via the AltOS "Configure Altimeter" feature to enable APRS and change my Frequency channel from the default. I also changed the APRS SSID value to 10. I left the Callsign field unchanged though as I thought broadcasting N0CALL would be good for testing purposes to highlight clearly whether or not APRSdroid is working. At this point I must mention that I was quite pleased to see the TeleGPS v2.0 was already running the latest firmware at the time of order, specifically v1.8.6.

Next up I had to give myself a bit of a crash course on the Baofeng UV-3R. It's not the easiest radio to operate but given the $23 USD price tag that's not entirely unexpected. Regardless, getting it up and configured was pretty simple once I wrapped my head around the UI.

To put it simply, it works! Instead of writing out the steps I took in long form here's a quick list of what I did to get everything to work.

On the Baofeng UV-3R
Set Frequency ex 434.550
Set VOX to 7

Connecting the phone and radio
Plug in Mobilinkd radio specific cable to radio and phone

On my phone in APRSdroid
in Preferences, click Connection Preferences
Make sure Connection Logging is enabled
in Connection Protocol, select Audio (AFSK)
Back out to main screen, click "Start Tracking" in the bottom right of the window

Once all that's done all that's required is to power on the GPS Tracker. Assuming it's configured to transmit across the frequency we're listening on (in the example above 434.550 MHz) then as soon as the radio starts receiving AFSK encoded APRS data it will be displayed in APRSdroid in the main tracking window. Once you see your transmitter (in my case N0CALL) then you can click on the entry to open up the log of that transmitter. When you do so you'll see a screen similar to what's below.



As mentioned above by enabling Connection Logging in APRSdroid you can store each packet locally to be reviewed or even shared at a later date. Post test I shared the log file to my Gmail account and in next to no time an email with the APRSdroid log file (aprsdroid-20180930-2011.log) in my inbox. Opening that file in Notepad ++ reveals a full log of all APRS packets I received during the test. Below is an excerpt of that file highlighting GPS lock had been achieved and GPS position and altitude data are being shared.



There are a few things worth mentioning.

1) I suspect this process will be a bit more error prone in terms of output when compared to the Altus Metrum telemetry offering. I also suspect that there might be more error in AFSK decoding over the phone when compared to using an inbuilt TNC. I'll test to confirm or deny this shortly.
2) Unlike the serial output from my Yaesu VX-8GR the altitude data is also being decoded via APRSdroid. That's great news.
3) The APRS SSID value configured on the TeleGPS displays in APRSdroid after the callsign. So N0CALL-10 is due to my callsign being N0CALL and my APRS SSID besing set to 10.

Now that I've got the Baofeng working I'll run the same gamut of tests on my Yaesu VX-8GR. One of the great things about that radio is I can have the above running (Mobilinkd cable + APRSdroid) alongside serial output from the TNC inbuilt in the Yaesu as my audio and data ports are separate. That should allow me to easily confirm if variations in position are due to incorrect AFSK decoding (my expectation) or if the GPS is actually spitting erroneous data as I'll have what should be two sets of identical data (excluding the altitude output of course).

Next up, Garmin, OpenStreetMap, and APRSdroid with OSM integration. We're getting there folks...

Hi Drew,

Just keen to hear how the Baofeng plus Android solution is going?

I am looking to get my first GPS tracker and will utilise my ham Radio Radio licence for an APRS solution. I already own a Baofeng and was looking at the Mobilinkd TNC, then read this post.


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[drew]

Hey Sirbad,

Sorry, I've not picked this up in quite a while. My Pixel that I was using at the time decided to brick itself December 2018 and when I moved to the 2XL I was greeted with a lack of headphone jack. I only recently picked up the Google USB-C to audio adapter, the cheap ones from Ali get rejected from my phone.

It definitely works though. I've just not done a side by side comparison since the last tests above.

If I get some time on the weekend I'll have a look at getting everything up and running on my new phone.

[Sirbrad]

Thanks Drew.

Don’t go to any trouble, I have decided to go down the Eggfinder path.

Cheers,
Brad


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[strud]

Solve all these complications and buy one of these radios

APRS decode, GPS Rx builtin, graphical display of remote station location etc

https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=111&encProdID=84807B1262BFED6AC816544D94D310E3&DivisionID=65&isArchived=0

[youtube]VFKLiowjNpo?t=924[/youtube]

[strud]

This might be better

[Sirbrad]

Solve all these complications and buy one of these radios

APRS decode, GPS Rx builtin, graphical display of remote station location etc

https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=111&encProdID=84807B1262BFED6AC816544D94D310E3&DivisionID=65&isArchived=0

[youtube]VFKLiowjNpo?t=924[/youtube]

Nice, but too expensive.


Sent from my iPhone using Tapatalk

[strud]

I agree that radio is not cheap but it is a true single device solution, no cables or other software anything and all in a rugged thing you can run around paddocks and in utes etc in the bush without it getting ruined/falling apart/cables dropping out just at the critical moment etc

Alternative is to make up something which of course is what Drew is showing. I guess a low cost android phone with the Baofeng radio double sided taped to the back of it would be close to a single device solution at a very low price.


In terms of being too expensive, I guess it comes down to how much time you have an what your priorities are That's only about 25 bottles of half decent wine, or 25 packets of cigs, 12 cases of beer, or less than one night on the pokies for some...... probably much less than the propellant cost of many rockets this would be getting used to track

I have a VX-7R and it is bombproof, reliable HT but no APRS or built in GPS. If I get another HT I think it would be something like the FT3DR.....

[drew]

I agree that radio is not cheap but it is a true single device solution, no cables or other software anything and all in a rugged thing you can run around paddocks and in utes etc in the bush without it getting ruined/falling apart/cables dropping out just at the critical moment etc

I second this statement. An APRS tracker/transmitter and a handheld with an inbuilt GPS chipset and APRS TNC is without a doubt the most simple and effective way to track and recover a rocket via GPS. You turn on the tracker, tune into the frequency via you handheld, and you're receiving packets. Is it a pricey solution? Sure. But as with pretty much everything in life you get what you pay for.

I did all the above tests because I wanted a better understanding around what my tracking options were and 'how' things can be integrated/cobbled together with other things. I did this as I was sick of running into weird issues when at the field and getting frustrated as a result. Anyone who's had issues with AltOS telemetry downlinks can attest to this. I wanted as much of a bullet proof 'fall back' option because redundancy is awesome. I primarily use TeleGPS trackers these days and my normal setup is as follows.

1) Altus Metrum telemetry downlink via a TeleDongle to my laptop. Teledongle is connected to a 5 element 70cm YAGI.
2) TeleGPS APRS beaconing every 5 seconds to my Yaesu VX-8GR. That radio is connected to either the stock whip or another 5 element 70cm YAGI. The Yaesu is also plugged into the laptop via a serial connection and I log all the incoming APRS packets in Putty as the Yaesu doesn't store anything, it just displays the last packet received.

I've chosen this setup as it gives me full physical receiver redundancy when compared to relying solely on one or the other. Having issues with the Altus telemetry link? No worries, I do a quick round of troubleshooting but if I can't get that working but I've got APRS packets coming in that show lock I can still proceed. If both methods aren't working I've definitely got a tracker/transmitter issue. Having the ability to isolate where the failure resides easily is a huge value add when you're in the field and most likely already stressing about your flight. The last thing you want to do is to have to wrap your head around electronics downlink issues when you're in that head-space. Ideally you want as much of your thinking done LONG before you are ready to press the button. By the time you're ready to launch ideally you want to turn things on, insert the igniter, and walk away. Having to think or troubleshoot issues is suboptimal at that point.

[OverTheTop]

That FT3DR looks seriously neat. If I were not spending so much on upgrading my 4WD currently I would spring for one of them instantly. Maybe I can get one as a Christmas present to myself!

Having redundancy on Rx is a nice feeling. I have been doing that for my past couple of flights, but with dual Altus Metrum setups.

[Sirbrad]

Would an FT2DR provide the same functions? Looks to have same features as the FT3DR. Might be a more affordable option.

So what are the options for a tracker besides telegps and bigredbee?




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