APRS - you cannot hide

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications.
It is mostly used for positioning data and weather reports.
Data is collected into the APRS Internet Systems (APRS-IS) which provides an easy graphical interface for the averga ham user, such as:
- map view based on Google-maps
- possibility to track a (mobile) station
- telemetry statistics of all (mobile and fixed) stations
- such telemetry may include e.g. weather reports or other technical parameters such as RX decoding efficiency

For a first overview see the Wikipedia entry.

In order to actively take part, the following components are required:
- FM transmitter with antenna
- GPS device
- a "tracker" device that converts the GPS positioning data into an AFSK1200 signal to be transmitted.

Possible setups can vary significantly in price and there are interesting options for true ham radio experiments.
For instance:

FM transmitter	GPS device	tracker	personal comment
up-to-date mobile TRX > 400 EUR ?	built-in included	built-in included	easy to set up, "plug-and-play", expensive
old handheld TRX rested in the shelf for years	Mobile phone with Android operating system always with me anyway	free App APRSdroid thanks to DO1GL !	good performance, fun to experiment

Receiving stations at exposed locations are required to shift the APRS telegrams (commonly transmitted in the 2 m VHF band) to the APRS Internet-System.
Such a station is called "Internet-Gateway" (short form: IGATE).

Again, a typical IGATE setup can vary heavily in performance, power-consumption and price.
For the ham willing to experiment, an effective setup can be built up from "old stuff" that you previously considered obsolete.

I have tested several setups and may dare to present a ranking, based on my experience.
It is splitted up into the separate modules of an IGATE so you may choose the one most adequate for you:

rating	RX	demodulator	runtime stability	power consumption	ease of setup
+ +	Wouxun KG-UV2D (handheld TRX) or Ham Master HM-800 (handheld TRX)	WX3in1 mini Digital Signal Processing	standalone commercial setup WX3in1 mini	Raspberry Pi or standalone commercial setup WX3in1 mini	standalone commercial setup WX3in1 mini
+	Realistic PRO-26 (handheld RX)	TNC hardware (remember the packet-radio age)	WiFi router running free open-source Linux or Raspberry Pi both running free APRS IGATE software	WiFi router	Laptop with WinXP running free UIView32
o	Commtel COM215 (desktop RX) or RTLSDR variant with R820T tuner	PC soundcard with free Dire Wolf	Laptop with WinXP running free UIView32		WiFi router running free open-source Linux or Raspberry Pi both running free APRS IGATE software
-	RTLSDR variant with FC0013 tuner	PC soundcard with free AGWPE		Laptop with WinXP

At my parents' farm - a top-hill QTH with a very good VHF propagation - I set up the very stable WX3in1 mini .
It is a stand-alone hardware solution with ARM-Cortex M0 CPU, digital signal processing and a very stable firmware.
The Ethernet output is connected to a stand-alone WiFi-client, connecting to the APRS-IS by a rather low speed (768 kbps) DSL connection.

An old Ham Master HM-800 handheld transceiver (courtesy of DF7IB / F5VIZ !) is used, connected to a X-50 ground-plane antenna on the roof:

The coverage is far beyond 100 km, see also the real-time receiver performance statistics from the APRS-IS.

The map below gives an overview of the RF telegrams received directly so far:

A second IGATE is set up in my flat in Kempten/Bavaria.

The first implementation used an Asus WL-500G Premium Wifi router, a vintage TNC2X and my handheld transceiver:

RF coverage is promising, as my flat is in the 6th floor with good propagation toward the west:

In the meanwhile the Wifi router has been replaced by a Raspberry Pi.

The main reasons are the massive conducted and radiated emission produced by the Wifi router itself.
Running the router, the RF spectrum up to 20 MHz was unusable.
The Raspberry Pi proved to be critical in the frequency range below 1 MHz only.

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