APRS – Bluetooth Adapter

The Bluetooth Adapter Rig

Cell in hand with Mobilinkd

Ok, so you dig the idea of the APRS setup outlined in my last article, Hardwired Cell, but maybe you don’t have the time to build the cable or you just want to be wireless from the radio to the phone or tablet. If that’s you, then let me introduce you to a setup that takes the audio cable out of the equation and replaces it with a nimble Bluetooth enabled TNC (Terminal Node Controller).

The cornerstone of this setup is the Mobilinkd TNC. It is an extremely small, lightweight TNC that links your Android phone or tablet or computer to your radio. Sorry, Mobilinkd does not currently work with iPhones. According to the maker, iOS lacks support for Bluetooth Serial Port Protocol (SPP).

I like the Mobilinkd TNC as it’s a very convenient solution. I’m especially anxious to see the other ways in which people figure out how to hack and repurpose this device in the amateur radio community.

The downsides?

I haven’t seen a mass produced case developed for it, yet. I have seen some prototypes from a third party that will basically extend the battery case on your HT to additionally house the Mobilinkd TNC. That would be nice. In the meantime I’m toying with the notion of mounting a HT and my Mobilinkd TNC inside a small Pelican Case with a clear cover. May 2014 Update: The Mobilinkd Bluetooth TNC now comes standard with a small, lightweight case. I have one and it does a good job of protecting the device when it finds itself floating around in my backpack.

– The Mobilinkd TNC uses a USB 2.0 Mini Type B jack (5 position) instead of the standard Android USB 2.0 Micro Type B jack. This wasn’t too bad since I still had some of these cables from an old phone. However, it would have been nice if all my devices were using the same cables.

The upsides?

– Unlike the Hardwired Cell, you don’t need a VOX capable radio. The TNC will trigger PTT.

– I’m looking forward to using this setup while hiking since the radio and TNC can be on my back and there’s no cable between that gear and my Android device.

– I spent a lot of time looking for the appropriate cables that I could salvage for the Hardwired Cell project. With the Mobilinkd TNC, you’re assigning value to your time.

– This is the quickest and easiest APRS setup that I’ve found, short of shelling out a few hundred dollars for an all in one HT. Plus, I’d take the user interface of APRSDroid over that of the APRS HTs any day.

– You can pair the Mobilinkd to Bluetooth capable computers, too. For example, I’m currently using it to run an IGate at my house in conjunction with an old Windows laptop.

Note: Before I go any further, let me put out a disclaimer. A lot of the material from the Hardwired Cell article has been copied over to this article where it is applicable. My intent was to prevent the need for people to reference other documents in order to get this setup off the ground. As a result, some of this is redundant if you’ve read both articles. On the upside, a printed copy of this page can stand alone.

For this project you’ll need:

1. A cell phone (with or without cell service) or a tablet to be the display, input device, GPS, and virtual TNC platform for this project. If you don’t have a suitable device, older used smartphones can be had pretty cheaply. Sprint offered to buy back my old HTC Evo a year ago for $25. Even with a little markup on their part, that tells me that you can get a device pretty cheaply for this project. I’ve used a Samsung Galaxy S3, HTC Evo, and Samsung Galaxy Note 10.1 for this sort of setup, all with success.

2. A radio. I used my HT, a Wouxun KG-UV6D. One of the great things with the Mobilinkd TNC is that you don’t need a VOX radio. The Mobilinkd TNC will trigger PTT.

3. A Mobilinkd TNC (http://www.mobilinkd.com/). These can be purchased online for $69.95. This device is extremely small and lightweight and is advertised to run more than two days on a single charge of its internal battery.

4. An audio cable to connect your radio to your Mobilinkd TNC. You can make your own, but at $9.95 to $12.95 (depending on the model of your radio), I opted to go with their cable.



This whole thing is dead easy.

Step One: Connect Your Radio to Your Mobilinkd TNC

Since this is the amateur radio equivalent of a flight attendant showing you how to use a seat belt, I’ll move on to step two.

Step Two: Pair Mobilinkd TNC to Your Device

Turn on your Mobilinkd TNC by pressing the blue power button. A blue LED should begin to flash rapidly. It will continue to do this until you finish pairing the TNC to your device.

Next, go to settings in Android and turn on Bluetooth.

Go to your Bluetooth menu and select “Search for Devices.” “Mobilinkd TNC1” should come up on the list. When you select the Mobilinkd, the system will ask you for a password. This is 1234.

Once you’ve successfully joined the Android device and the Mobilinkd TNC, the LED will slow to a couple of flashes every few seconds to let you know that it’s still alive.

Step Three: Install and Configure APRSDroid

Note: If you’ve already done this step for the Hardwired Cell, you can skip down to connection protocol (11) and connection preferences (12). Everything else is the same.

Go to the Google Play Store and buy APRSDroid. At the time of this writing, it’s only a few bucks and well worth everything that its creator is asking. Once you have it installed, we’ll do some configuration.

1. Go to preferences.

2. Enter in your callsign. In APRS you’ll often see stations with an additional identifier after their call. This is to delineate between different stations that they may own. When APRSDroid says “without SSID,” they mean without the additional identifier. Just enter in your FCC callsign.

3. Assuming that you don’t already have an APRS-IS passcode, request one through the link in the preference menu now. APRS has an internet backbone. It’s what lets you see radio traffic through websites like APRS.fi. It’s also what lets APRS text messages reach beyond the local area. Note: APRS-IS will require proof of your license, as they should. You will be passing traffic across their network that will eventually cross the RF line. They have a duty to verify that you are licensed. If you’ve registered for a service like Echolink, then you know what I’m talking about.

4. Once you get your APRS-IS passcode, write it down somewhere safe (you will forget it) and type it into APRSDroid.

5. SSID. Choose what type of station you are. In my case, I use -9 because I run this setup in my car. As you can see from the drop down menu, there are several options available.

6. APRS Symbol. This is one place I think the program should include additional information. In short, there are a bunch of different symbols that can represent stations on an APRS map. The only way to know what is available is to look at a chart such as the one here. http://www.aprs.org/symbols.html

The Cliff’s Notes version is this: /- if you’re a house, /> if you’re a car, /k if you’re a truck, /v if you’re a van. There are many more options, but this will get you started. I recommend ditching the default /$ (a phone handset) unless you’re using APRSDroid exclusively through the cell network.

7. Comment field. This is how you let people know how to reach you. If you had a slick Kenwood or other APRS integrated radio, this field would auto populate with the frequency that you are monitoring. While it can be a hassle to keep up with, I recommend that you try to do the same as it will be particularly helpful for people passing through the area. Maybe one of repeater frequencies and tones? I’ve also seen people put email addresses here, but beware of spambots that crawl the internet (your radio packets will end up on the internet if an IGate hears them). Remember, the goal is communications, not vehicle tracking. If you don’t tell people how to communicate with you, then you just have a ham based LoJack.

8. Unless you’re a base station, I’d turn SmartBeaconing on. Some software decides to update your position after a set amount of time regardless of whether you’re moving or not. SmartBeaconing knows to transmit more frequently when you’re moving quickly or when you’re changing direction.

9. Location Settings. This is where you fine tune SmartBeaconing. For a fixed station, any reporting more often than once every 30 minutes is a bit overkill unless you’re a weather station. 15 is the recommendation there. Remember, unlike your computer, if there is a packet collision, the packet isn’t resent in this system. Overloading the frequency means preventing messages from getting through. Northwest APRS, one of the best organized regional APRS booster organizations in the US, recommends no more frequent updates than the following for mobile stations:

If using no relay or WIDE1-1, 1 min.

If using WIDE1-1,WIDE2-1, 2 mins.

If using WIDE1-1,WIDE2-2, 3-5 mins.

WIDE2-2 is the recommended path setting for fixed stations, WIDE1-1,WIDE2-1 for mobile, and WIDE1-1,WIDE2-2 is ok if you’re in a very rural or mountainous area. More on paths in a little bit.

APRS.net recommends the following speed settings for normal driving:

Fast Speed – 60 mph or 97 kph

Fast Rate – 180 sec

Slow Speed – 5 mph or 8 kph

Slow Rate – 1800 sec

Min Turn Time – 15 sec

Min Turn Angle – 30 deg

Turn Slope – 255

10. Position Privacy. If you want someone to know that you’re in radio range, but you don’t want them to know what specific house or store you’re parked at, change your position ambiguity. I personally use setting 2 and for my purposes, I turn off speed, bearing, and altitude. If I was tracking a balloon launch, I’d want all of that. For a mobile station, I just want people to know I’m in radio range. You could make the case for enabling the speed setting, though, so people can deduce that you may not actually be in your car at the moment (it’s parked?).

11. Connection Protocol. Select Bluetooth TNC.

12. Connection Preferences.

Client mode should be checked.

Your Mobilinkd TNC should be selected under TNC Bluetooth Device.

I made no changes to Channel (blank), TNC init string (blank), and TNC init delay (300).

Bluetooth settings… this should take you to Android’s Bluetooth settings. No changes needed here.

APRS digi path. This is the main thing that you will want to change in this menu. See step 9 for the discussion on digi paths. NWAPRS.info is a good source for descriptions on how the path process works. The quick answer is, you probably want “WIDE1-1,WIDE2-1” if you’re mobile.

13. Keep Screen Awake. I ride with my cell phone mounted on my dash like a GPS allowing me to see who is nearby. If that’s you, you’ll want to enable “keep screen awake.”

Step Four: Configure Your Radio

1. If you’re in North America, the APRS frequency is 144.39. For other countries, see APRS.org. Note: It is possible that this frequency can deviate in your area to handle special event traffic or to balance heavy network loads.

2. Adjust squelch so that weaker packets aren’t blocked.

Step Five: Start Tracking

From the Hub or the Log, hit start tracking. If everything is correct, you should start seeing packets soon. In the Log, you will see all the data received in a packet. In the Hub, you only see the most recent report from a station in order of station distance. Switching over to the Map will display those objects against a map. If your cell phone or tablet is online, the objects will be superimposed on a Google Map. If you’re offline, the APRSDroid website has instructions for downloading and installing OpenStreetMaps for offline use. I’ve used both and while I prefer Google Maps, OpenStreetMaps works fine for internet free operation.

APRS On Dash

Congratulations! If everything is working, you’re part of the APRS network. If not…

– Mobilinkd has its own program on the Google Play store that you can use to troubleshoot your audio levels. This is a huge advantage over the Hardwired Cell as it will allow you to know if you’re over or under driving the audio.

– Is your radio opening squelch fast enough to capture the whole packet? Keep in mind that APRS has no error correction. If the receiver doesn’t catch all of a packet 100% accurately, the packet is no longer decodable.

– To confirm that your packets are getting out, use a second radio to confirm the transmissions. Keep in mind that websites like APRS.fi will only display things that the IGates heard. You may not be in range of an IGate or a Digipeater that is.

– If you find that objects are disappearing from your Hub or Map, check your Show Last settings. It’s possible to limit packets to only those received in the last 30 minutes. If you want to see objects beyond that time, adjust accordingly.

– When I got started in APRS, I thought my setup was broken during many commutes. Through testing, though, I’ve found that there are just some places in the Nashville area with lousy APRS coverage. 840 between Nolensville Pike and I-24 or I-24 from 840 down to Beech Grove are two examples. This will change as Digipeaters go up or down, but keep in mind the dead spot issue when you use APRS.

– HTs are the easiest way to build this setup. However, remember that HTs, especially in a car, have serious limitations. If you want to improve this setup, the cheapest and easiest step is mounting an antenna outside the vehicle. The factory rubber ducks barely cut it for voice. When a voice gets choppy, you can sometimes still make out what is being said. Packet radio is not that forgiving. If any part of the packet is unreadable, the whole packet is lost. I’ve run my Wouxun in my car off of the standard rubber duck and a proper 5/8 wavelength mobile antenna. Counting packets across the same commute, I pull 49% less packets with the rubber duck inside the vehicle. When inside the house and out of the metal cage that is my vehicle, I do a bit better. Typically the rubber duck in that scenario only misses 25% of the packets that the other setup gets. Bear this in mind when you think your Mobilinkd TNC or APRSDroid is failing you.

– New (1/22/15) Want to connect the Mobilinkd TNC to a Kenwood TM-281A? Check out this diagram.

Credits and Links

To Rob of Mobilinkd.com. I dig the innovation. Keep it coming.

Thanks to Georg Lukas for APRSDroid. You’ve saved me a lot of money. 

Thanks to Bob Bruninga, WB4APR, for starting APRS 21 years ago and continuing to advocate for it. For more info on APRS, go to www.aprs.org. APRS is a registered trademark of Bob Bruninga.

APRS.fi is my current favorite APRS tracking website. In the context of this article, it’s a good tool for checking to see if your packets are getting out to the world if you don’t have a second radio and you live close enough to an IGate or a Digipeater that can get you to one.

– Dallas, K7DCC

This page was created 3/12/2014 and updated 1/22/15.

Click here to return to the main WCARES APRS page.