On the air with APRS

  I've played around with APRS for several months now, but it's mostly been done through the internet (i.e. APRS-IS) with a phone or a tablet. 

The Android app, APRSDroid, is on my "old" Nexus One, my 2012 Nexus 7, and my Samsung Galaxy S4 GPE. The app uses your device's GPS and internet connection (cell or Wi-Fi) to send your location to the APRS-IS service, where it becomes visible to the world. You have to get an APRS-IS passcode in order to use the app, which verifies that you are a licensed amateur operator, and you need to know your Maidenhead grid square (e.g. EN35ja) in order to do so. I've been using the app with a cellular data connection when I drive around, and it certainly works.

Technically, since the app uses cell or Wi-Fi -- which is radio, after all -- I could say that I've been using RF. But I wanted to get an idea of our local APRS digipeater and gateway coverage, and see if it was really practical to use an HT at relatively low power for this kind of digital communication. In order to do that, I needed a TNC to translate the analogue audio on my HT to a digital format that the gateways and digipeaters could use. I looked at my options, and went with the new Mobilinkd TNC2. 

The TNC2 is battery-powered and uses Bluetooth to connect to your phone or tablet. In a previous post, KD0WBK (Bob) explained how to use one of these. The TNC2, however, now comes in a case and has a few other upgrades over the TNC1 that Bob documented so well. 

Actually, as the manual explains, the TNC2 isn't a TNC at all; it's a KISS modem. But it still does the job, and your phone provides the "brains" that the modem lacks. It cost $75, including a Kenwood-style cable and shipping. Other cables are available for other radios for a little more. 

I wanted to use my (monoband VHF) PuXing PX-777, which has the same Kenwood cable as many other HTs like BaoFeng, TYT, etc. It was pretty easy to set up the radio. I just had to program 144.390 (no offset) into the memory and turn the squelch level down to "1". Later, I had to make a simple volume adjustment.  

The TNC2 was a bit more involved to set up, of course. First, you have to charge it. There's no charging cable included, and I was fortunate to have the proper mini-USB cable around. In less than two hours, the red LED had turned off and I was ready to configure it. To do this, you need to download and install the Moblinkd configuration app, and you should also download the pdf manual. Then you need to turn the TNC2 on and pair it with your phone or tablet using Bluetooth. Pretty easy. 

I'm not going to duplicate the manual here, but I'll summarise. The volume of the radio has to be set at the proper level in order for the TNC2 to convert the analogue squawks and screeches to the digital AX.25 format. Then you need to make a quick adjustment of the TNC2's volume level with another radio on an unused simplex frequency. Last, you have to change the settings on the APRSDroid app to work with the TNC2. 

I didn't have any problems doing this, and it didn't take very long. Once it's set up, you don't need to mess with it again. Well, you might need to adjust the volume on your radio, but I just marked the proper spot on the case next to the volume knob. 

When I set it up, I had the stock duck antenna on the radio and I was (of course) indoors. I didn't think that this arrangement would be good enough to get a signal into the network, and I planned to attach the radio to my outdoor antenna. Well, I was wrong. 

Immediately, the log screen on the APRSDroid app started showing stations being received, and it showed that my packets were being picked up by the Robbinsdale K0YTH-13 digipeater and the W0YC-5 gateway at the University. I verified that my location was showing up on the map at aprs.fi, so I knew that it was really working. Using the map view on the APRSDroid app, I could see the location of every station that my HT was picking up. I was on the air! 

The battery on the TNC2 is supposed to last for two days without charging, but I haven't had it long enough to verify that. I'm not sure that my PX-777 can go that long on a single charge, anyway. All that I have to do is put the HT in the car (with the TNC2 attached) and connect it to the antenna. My phone is with me anyway. 

There are, of course, radios out there that have APRS built in, such as the new Yaesu FT1-DR HT. But this is a cheap and flexible option, and a relatively painless way to dip your toe into the waters of packet radio. 

I'm looking forward to testing the coverage of the local network. But, based on this initial experience using an indoor stock duck, I feel optimistic about being able to access the APRS network in the metro.