Very simple and inexpensive way to receive APRS data

[DaveW6DPS]

I have been playing with an idea I stole from a post to a 4-wheel drive ham club forum.

A full-featured HT with built in APRS capabilities is rather expensive, so I was looking into a simple and easy way to receive data with stuff I had on hand.

This method basically uses a suitable receiver, simple interface cable, and software called APRSDroid to receive APRS directly on your Android phone. There may be similar software for Apple, but I personally don't do Apple.

My write up is at: https://www.qsl.net/w6dps/APRSDroid.html

There are a couple of other things pertinent to rocket tracking on my project page as well. I would welcome comment and suggestions. I do not do very fancy projects; my projects tend to be a simple way to do just to get the job done.

 

[jderimig]

Have your searched the term "APRSDroid" on this forum to see what others have experienced and tips you may offer? APRSDroid is not exactly unknown of in this community but you may have solutions for issues others have noticed.

 

[plugger]

Thanks for the post Dave. I find it both interesting and timely. I was about to order a Mobilinkd (https://www.mobilinkd.com/) for this exact purpose. Instead I reckon I'll give this a crack as it looks like it'll do exactly what the Mobilinkd does (APRS TNC) without the added cost. I'm solely looking to use this for rocketry tracking over APRS so it definitely looks like it'll fit the bill.

Now, onto the variable, cabling. Would these cables that Mobilinkd sell work as a drop in solution for this use case?

https://store.mobilinkd.com/collections/tnc-cables

My expectation is that they would work as the Mobilinkd 3.5mm interface is a 4 pole TRRS audio connector. Can you confirm? If so it looks like I'll be ordering some tnc cables from Mobilinkd shortly!

 

[FMarvinS]

Interesting, doable project. I enjoyed reviewing your other web page projects. The tracking transmitter on that page is also simple and interesting. However, an Amazon product review (of the transmitter) showed that the range, even with tuned antennas, is rather short. You may want to consider a 1 Watt DRA818U UHF radio module (70 cm band), which costs less than $25 instead of the transmitter purchased from Amazon. Others have used this inexpensive versatile transmitter for GPS and tracking (see "talky GPS" project under electronics at: https://nerorockets.nl/). The "talky GPS" project integrated with an arduino too.

Fred, L2
ICBM member, Camden,SC
KG4YGP

 

[BrAdam]

For those that use iPhones, PocketPacket (free) works in the above scenario. Also have not confirmed it yet but I believe APRSproUtilities (pay only for transmitting) does as well.

 

[ksaves2]

Been a long time I tested APRSDroid but diddling with TNC setting with an outboard TNC is one of them. Use a Mobilnkd TNC and make darned sure you don't jostle the volume control or messing up the gain can dork your decoding.
The only problem with APRSDroid effecting a recovery is when navigating out to the rocket, in order to get your local position to change you have to have APRSDroid transmit a position packet for your local icon to move.
It will not move automatically. You don't want the program set to automatically transmit a position based on time because that could interfere with decoding the incoming positions if your local is transmitting over an incoming packet during
the rocket flight. Just set it for manual transmission only. It's a quirk but can be used if one wants to use it. I had a test rig for a Wildman Jr with a J of some kind that hit 6k and was completely out of sight. My primary recovery rig was
the tried and true Kenwood D72A wired into a Garmin 60Cs (or a 60CsX would work too). No diddling with that setup. Just plug and go. The APRSDroid setup was a Nexus 7 2013 with a Kenwood Th-F6A and Mobilnkd TNC. The Nexus system stayed
at the LCO table. It worked fine showing the flight and when I recovered with the D72/Garmin, the Nexus/Droid system showed the walk back. The flight was recovered .8 to 1 mile away and the main came out fine. Weird thing was at that distance we didn't any of the events visually but saw the positions on the map. I blow the main up 1200' and could tell it was coming down nicely due to the slower descent rate seen on the screen. One can set the Kenwood to show the altitude only and I don't bother with lat/long because that is sent to the Garmin and is displayed on the map-in-the-hand. The Wildman Jr. was lying on the ground with the fully deployed chute system without a scratch on the paint.

APRSDroid is workable except get the TNC set exactly right and do a range check. Don't jostle the radio volume control and remember you'll have to send an position packet out (which is no big deal once the rocket is down) in order to
get your local position on the APRSDroid screen to move. Kurt Savegnago

 

[DaveW6DPS]

Now, onto the variable, cabling. Would these cables that Mobilinkd sell work as a drop in solution for this use case?

https://store.mobilinkd.com/collections/tnc-cables

My expectation is that they would work as the Mobilinkd 3.5mm interface is a 4 pole TRRS audio connector. Can you confirm? If so it looks like I'll be ordering some tnc cables from Mobilinkd shortly!

The Mobilinkd cable is not compatible. BTech does make a cable for some of their HTs. I haven't used it, but it looks good.

https://www.amazon.com/dp/B01LMIBAZW/?tag=skimlinks_replacement-20

 

[plugger]

The Mobilinkd cable is not compatible. BTech does make a cable for some of their HTs. I haven't used it, but it looks good.

Actually, I can confirm that the Mobilinkd Baofeng UV-3R cable is compatible for use with APRSdroid. I received my cables late last week and did some testing over the weekend with my Baofeng UV-3R, Mobilinkd UV-3R cable, and my Pixel XL. Transmitter was a new TeleGPS that I had yet to change the Callsign on, hence the N0CALL

It makes sense the Mobilinkd cables would be compatible as they're TRRS plugs on the phone end and custom/specific pinouts for each radio. I've also got the Yaesu VX-8GR cable and I'll test that one in the next few days.

I'm quite impressed the Altitude field is passed via AFSK to APRSDroid if I'm being honest. I wasn't able to get that to occur with the serial output via my Yaesu VX-8GR and it's a nice field to have.

 

[DaveW6DPS]

The tracking transmitter on that page is also simple and interesting. However, an Amazon product review (of the transmitter) showed that the range, even with tuned antennas, is rather short. You may want to consider a 1 Watt DRA818U UHF radio module (70 cm band)...

Fred, L2
ICBM member, Camden,SC
KG4YGP

That module looks interesting for other projects. I see there is also a VHF version. Thanks for the suggestion!
For the project you referenced it would be too big, heavy, and take too much power. The ISM module I use has enough range for small model and mid-power rockets it is intended for, and will fit in a 24mm body tube. I have tracked it to about 3000 feet AGL and almost a half-mile downrange.

 

[plugger]

That module looks interesting for other projects. I see there is also a VHF version. Thanks for the suggestion!
For the project you referenced it would be too big, heavy, and take too much power. The ISM module I use has enough range for small model and mid-power rockets it is intended for, and will fit in a 24mm body tube. I have tracked it to about 3000 feet AGL and almost a half-mile downrange.

Another module worth checking out is the HopeRF RFM23BP ISM Transceiver. It can do 433/868/915MHz ISM bands at 1 Watt with and 18mm x 31mm x 2mm footprint.

 

[ksaves2]

I will caution again that if APRSDroid is being used, it's advisable not to skimp on radio quality. The cheap radios have cheap receivers that
can make it difficult to decode packets. Also, accidentally hit your volume control and your ability to decode positions is impaired.
One has to have the Mobilnkd setup precisely for a given tracker. I had the gains in mine that allowed my setup to hit the local digipeater
and be propagated over the APRS network. The only problem was my D72A couldn't decode the position that was sent by the Mobilnkd
directly. I diddled with the settings on the Mobilnkd and the D72A could then decode the position but then the local digi couldn't "hear"
the Mobilnkd generated position. Again, I find to get one's local position to change on the map, they have to send a position to get the local
"icon" to move on the map. No big deal but one has to keep that in mind if they are trying to recover a downed rocket.

One gets what the pay for and the bullet-proof choice is a D72A/VX-8GR with one wire or cable to a GPS mapping program. No diddling with gains or settings. Just works. (The D74A will work fine but that rig is extremely pricey and if one has no use for the D-Star stuff, it's a waste.)

For that matter can do software decoding from a tablet now. I was messing with that with a laptop 10 years ago and it's too much work
and lose a setting or get on the fringe and lose position packets. Cheap receivers in cheap radios are fine for repeaters but for pulling a signal
out of the fringe, you get what you pay for.

It's a sick feeling to not get reception on a flight. Happened to me twice 11 years ago when I just started out. Found one out of the two rockets
in good order.

Easiest for tracking and not to save data is the D72a/-8GR wired to a round port Garmin 60Cs or 60CsX. The Garmins can be had used. A monochrome
Legend can work as there is a cable available for it but I didn't like the display.

I go back to the days of a Celeron laptop and a TNC-X for a base station plugged into a Kenwood TH-F6A. F7A(g) plugged into a Garmin I used to walk out to recovery. Needless to say, I spent more time diddling than flying when operating the base station and stopped doing that and used the radio and the Garmin thereafter. Did learn a lot of "rocket" behavior at altitude under drogue by tracking others Beeline GPS trackers though. Kurt

 

[plugger]

Hi Kurt,

Here's my planned tracking setup for TeleGPS use. BRB will be the same sans Altus Telemetry.

Primary tracking station for Altus Metrum Telemetry
- Win 10 laptop, TeleDongle, TeleGPS 1.8.6 software. Arrow 5 element Yagi (440-5). This will stay on the flight line post flight.

Primary tracking station for APRS
- Yaesu VX-8GR, inbuilt TNC, Garmin 60CSx with Australia roads and topography map preloaded. Arrow 5 element Yagi (440-5S)

Secondary tracking station for APRS
- Yaesu VX-8GR, Mobilinkd cable, Pixel XL running APRSdroid (possibly with OSM maps for offline use if required)

Benefits are as follows.

1) Altus Telemetry should provide the most accurate in flight telemetry data but lugging a laptop on recovery sucks. Hence APRS for the recovery.
2) If the TeleDongle and TeleGPS have issues instating a connection having APRS beaconing at 5 second intervals will provide me with

• confidence that the GPS is working, has lock, and is logging.
• a simple way to ensure a field friendly way of recovery

3) Using the primary APRS setup for recovery should be incredibly simple. Data port from 8GR to 60CSx. As you've said, accurate and dead simple.
4) Having the secondary APRS setup for recovery, whilst not being as accurate as the inbuilt TNC option on the 8GR, should provide the following benefits.

• full logging of all APRS traffic locally on phone with the ability to extract all logged data. (including Altitude which doesn't output via serial from the data port)
• APRSdroid satellite imagery overlay for a "birds eye" view of where the rocket is located.

5) If I do happen to have cellular reception I'll also use Google Maps and paste my last packet GPS coordinates to provide a hybrid overlay image of the location of the last received packet.

While the above does appear somewhat complex it's actually quite simple to configure and connect together. All of the APRS stuff is preconfigured and automagically works when I plug things in.

The Baofeng UV-3R will be my Backup tracking station for APRS. I've got a Nexus 5X to hang off it to run APRSdroid only if the primary has issues.

If you haven't noticed by now I like redundancy. I've still got to test the VX-8GR to ensure I can run both APRS tracking systems simultaneously. But I can't think of any reason why it shouldn't, each has its own port to output data from.

As to the "diddling" realistically everything will be preconfigured and plug and play. My phone will already be in my pocket so why not use it and a Mobilinkd cable to connect my phone and radio?

The most fiddly bit of the entire setup from my experience is the Altus Metrum telemetry radio initialisation.

 

[ksaves2]

Ummm, You shouldn't have a lick of trouble as long as you can get all that stuff setup. The 8GR with the Garmin is the most bulletproof of the lot. I take it you're feeding the 60CsX with a cable?

The GR with the Mobilinkd one is essentially just using the audio receiver of the 8GR for the purposes of sending the positions to they map with the Mobilinkd but you'll
also be able to see the waypoints on the screen of the GR. If you can get the 8GR's to display the altitude on the radios screen you'll have direct feedback on that
important parameter. I like to do that with a Kenwood D72A and I'm more worried about confirming the apogee and main events have occurred during the flight. The
live altitude readout is what I pay attention to during the flight. I may throw a glance at the map but stay concentrated on the altitude. When it gets close to
the main chute deployment, I look at the map than look up in that expected direction when the rocket is close to the main chute deployment. That's GPS altitude minus
field elevation (field elevation is the GPS altitude while on the pad). If I get a look of the rocket under main, great! If not, I get focused on the altitude descent because
sometimes you can discern that the main is out even though you can't see it at a distance. That can be had because the descent rate slows. If the main deployment is relatively low
and the rocket is very far away, you might not be able to make that determination due to Loss Of Signal (LOS).

If you have more than one person who can monitor, use one to call out the altitudes and one who can call out the direction and distance. The altitude person can call out that the
main deployment is coming up and the "map person" can call out the direction to look for the expected main chute. That way a bunch of eyes can be looking. A visual confirmation
is always nice to have if possible. Of course sometimes it might be so far away that even if everything goes properly, it might not be seen. In that case you might be able to infer
a proper main if enough data comes across before touchdown. Sometimes if the venue allows, it might be better to blow the main up higher so there is more time to get some fixes.
It's a tradeoff though if the winds are higher might carry it further out of range. Judgement call here.

I have a 10 inch Chinese Windows tablet with an onboard GPS (you won't find them anymore like that) that works well with a Tele-BT and Tele-GPS using
APRSIS/32. Can even be hacked for the NMEA trackers but takes more finesse. Tablets need external batteries as you'll have the screens turned all the way up
and you will need a shaded area to view them. I stick the tablets inside a flat black painted box for a portable sun shade.

One bit of advice with multiple ground stations. If multiple setups depend on Bluetooth links to peripherals, I find it's best to setup one ground station and then take the second one
and walk out of Bluetooth range of the first station and do the setup out of range of the 1st station. I once got so freaking confused I gave up on the backup station and flew with one ground station monitor.
My second station was detecting the first stations devices and I got confused what was what under the pressure to fly. If you go out of B/T range of the first device it's easy to see your desired peripheral, get
it paired and then you can walk back to your 1st station without issue.

I then went home and figured out how to pull off the setup and got the multiple ground stations up. Practice your setup with a tracker running in a non-stressed environment before a launch to be
certain you can get all three stations doing what you want them to do. It's harder when under the pressure to launch so it's best to have the bugs worked out before you go to the field.
Good luck and have a great launch! Kurt Savegnago