One of the first things that I tried with a VHF transceiver was to transmit the GPS position over the APRS network. The easiest way is to directly connect the VHF transceiver to a mobile phone, with Android operating system, which runs APRSdroid application. This application is an Open Source Software, developed by Georg Lucas (GE0RG). Is only a single 'e' difference from the name of "Star Wars" creator (HI), but the application is just as successful as the movie, at least among the radio amateurs using the APRS network. And, not to mention that, both creations are based on androids (HI, again). The release history of the application, including the latest version, can be found at the following link: http://aprsdroid.org/download/.
If you want to transmit only the GPS parameters (tracker mode), you can download and install a version older than 1.0. The only advantage of installing a 0.x version would be a lower memory usage of the mobile phone, in case that you own an older device. But, I strongly recommend at least 1.2.0 version.
Now, in order to send only the GPS parameters you need to prepare an audio cable, like in the picture below.
On the phone side, the following settings must be made in the APRSdroid application (1.x versions):
your Callsign (without SSID);
APRS-IS password: optional, mandatory only if you wish to use the application for APRS-IS (Internet Service);
SSID (Secondary Station ID): the usual values for this parameter can be 7 for handheld radio, 9 for mobile radio stations or 10 for APRS-IS;
APRS Symbol: this is the object displayed on the APRS map. I use /- (home symbol) for fixed activities and /> (car symbol) for portable/mobile activities. When the phone is used in APRS-IS network, based on Internet connection, youcan use the /$ (phone symbol). A very useful symbol in emergency situations is \! (exclamation mark). But, please note that because emergency beacons are properly supported in the MIC-E format, some APRS applications will not rise an alarm when the symbol is present. The correspondence between APRS symbols and ASCII characters can be found here or here;
Comment field: enter an information text, which will be transmitted after the GPS coordinates;
Location Source: set on "GPS/Network Position" and configure the Location Settings with the update time and distance values according with your status: fixed/portable (0 distance and long time values, more then 10 minutes) or mobile (at least 3 minutes and 5 kilometers);
Optional, you can send additional motion parameters (speed, bearing and altitude) in Position privacy settings;
Connection Protocol: this must be configured as "AFSK via Speaker" or "Äudio (AFSK)" in newer versions. If you use a 1.2.x version it is recommended to set Audio Output to "Voice Call" option.
APRS digi path: the default value is WIDE1-1. This ensures that your APRS sigs will be sent to Internet (APRS-IS network) by the digipeater or the I-Gate which receive these sigs. If you would like to be relayed further by the digipeater, this parameter should be set to WIDE2-2 (fixed stations) or WIDE1-1,WIDE2-1 (mobile stations). This parameter will be set to ARISS value when you intend to sent APRS packets via International Space Station.
On the transceiver side, you have to set the VOX value at a non-zero value. And, don't forget to set the right frequency assigned for your APRS area. A very good map containing the world wide APRS frequencies is provided by G6UIM:
With all the above settings, after you connect the two devices with the proper cable, you must press the <Start Tracking> button in the APRSdroid application. After the application establishes an accurate GPS position, according with the value set for "GPS Precision" parameter (in Periodic GPS/Network Position proprieties), an AFSK signal will be generated, which should enable the transmission on the transceiver. If not, try to increase the audio level at the phone output, using the volume button or the internal phone software settings.
The next challenge is to use the APRSdroid application in a two-way (bidirectional) mode. This will be a real challenge because the success in bidirectional mode, using only a simple cable, is highly dependent by the phone model.
First, you need to change the audio cable's configuration as follows:
The APRSdroid software configuration remains the same and, after you start the APRS tracking, continue with the transceiver's audio output level adjusting, in order to find the right threshold for decoding of signals by Android application.
At this point, you have to accept that not all Android phones work with this cable ! As example, from my experience, Sony Xperia smartphones reject rapidly the cable, with the message that it is an incompatible accessory, while most of the HTC, LG and Samsung Android devices behave well. But, again, not all !
I started the experiments with a HTC Gratia, with very good results. Things have not been the same with HTC Wildfire S, the replacement of HTC Gratia: the phone started the audio player when a signal received by the VHF transceiver was injected in the phone's input. Same with HTC Desire S. In these cases, but also with other phones, I solved the issue with a very smart application, which, of course, in other conditions, I would overlook it: DisableAudioPlay. Can be found on Google Play Store or can be downloaded from here.
A short demonstration about how APRS messages can be send via International Space Station, using only a simple cable between APRSdroid and a VHF/UHF handheld, can be view in the below movie:
In this test, I used MAAS AHT-2UV transceiver, with 5 Watts power in a multi-band whip antenna, MAAS HVT-400, placed on the car's roof.
And, there would be another finding, maybe will helps: you will have more chances to receive APRS packets on a large range of smartphones if a 4-poles cable from a headset will be used. With other words, take any smartphone headset with 3.5mm 4-poles jack, cut the cable below the microphone and solder it to the jacks which must plugged in the transceiver, following the above wire map. I don't know why, but this cables will work better then those with a 4-poles jacks soldered by yourself, which in some smartphone behave like an imperfect contact on the input side.
So, one thing is sure: transmitting APRS packets works for sure with many Android phones, but receiving remains a research field. For this reason, you can try the next level: using a Bluetooth audio channel instead the cable.