[aprssig] GPS & Display Ideas

Stephen H. Smith wa8lmf2 at aol.com
Tue Aug 20 17:23:39 EDT 2019

On 8/20/2019 11:09 AM, KB5ILY - Travis W. Burton wrote:
> At our monthly Amateur exam session this past Saturday nobody showed up to 
> test, so that left the 4 VEs to find something else to do for a while, have a 
> discussion of things.   One of the subjects that came up was APRS, and it 
> ended up going this way...
> 2 Kenwoods, a Yaesu and my Alinco; all have built-in TNCs so there is a data 
> port for GPS input on all.  Can we do any or all of the following; A.  Use 
> retired cell phone as GPS.
> B. Use an Amazon Kindle, Apple iPad or other such tablet (with or without 
> internet access, but *not* accessing APRS-IS) as station map display?

Basically,  NO to all these questions...

1)    Most of these devices have NO WAY to export data from their internal GPS 

2)    All the ham APRS radios require classic 4800-baud RS-232 *SERIAL*    
NMEA-0183-format   GPS data input on a physical serial port.   Not Bluetooth.  
Not USB.  REAL serial only.

3)    Cell phones normally don't have classic serial ports.  If there was any 
way to get GPS data out of a phone or tablet, it will be in a proprietary 
binary format  via USB or Bluetooth. (Rather than the plain-text generic NMEA 
ASCII output all  ham APRS gear requires)    Further, Apple "i-Gadgets" without 
cellular radios in them (ipods and low-end WiFi-only iPads) have no GPS 
receiver in them at all.   Not sure about Android non-cellular tablets.

4)    Since phones and tablets don't normally have serial ports, it would be 
very difficult to get any decoded APRS posits out of the radio's built-in TNCs 
and into the external device.  Assuming there was even any mapping app on any 
of these devices that could plot such data.   At the least, you would require 
some sort of serial-to-Bluetooth converter.  This will cost substantially more 
than just buying a GlobalSat BU-355 or u-Blox serial GPS to plug directly into 
the radio.

The only feasable way to use a phone or tablet as a mapping display for an APRS 
radio would be to take the received audio on 144.39,  from a 6-pin mini-DIN 
"data port" (actually TX and RX audio) on the radio. Feed the audio  into the 
external headset mic-in jack on the phone or tablet.  There are dedicated APRS 
apps for both iOS and Android that can use the phone or tablet audio system  as 
a soundcard "soft TNC".  In turn, these apps are dependent on constant access 
via cellular data to Google Maps for the map display.    This, of course, 
assumes your mobile device still has an analog 3.5mm TRRS jack for audio in and 

There is one car navigator display GPS that can function as an APRS mapping 
display for the Kenwood APRS radios or an Opentracker 4 TNC.    The AvMap 
Geosat 6 is a 5" display GPS that can plot APRS posits heard on a Kenwood APRS 
radio. It's internal GPS receiver can talk back to the Kenwood in compatible 
serial NMEA format.   It's expensive and appears to be discontinued...


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

Live Off-The-Air APRS Activity Maps

Long-Range APRS on 30 Meters HF

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