Overlanding with HAM Radios

Molly has two HAM or amateur radios. One is permanently fixed in Molly and acts as our mobile base station, going wherever Molly goes. The second is a portable or handheld radio which can go with us on walks. These two HAM radios are a great addition to the rest of our communication equipment, especially for local area communication.

Permanently fixed in Molly is an ICOM ID-5100A dual band radio. This radio has a few features which make it an excellent choice for overland travel. Most importantly it can operate in the VHF or 2m band frequency, which gives around 5 to 10 km range, and even further if a repeater is available. It also supports D-Star, a digital mode that transmits around the world when connected to the repeater. Lastly, it supports GPS reception from other D-Star capable radios – more on that in a bit. Our handheld radio is a Kenwood TH-D74a tri band radio. It also supports the D-Star digital mode and the transmission of GPS coordinates.

We are still experimenting with these HAM radios and finding out the best way to use them. So far we use this setup to keep in touch when one of us goes for a walk and the other stays back at Molly. We also tune into the Weather band on a regular basis to get local area weather reports and forecasts.

2m Band Communication.

The 2m band is ideal for point-to-point communication, this could be for vehicle to vehicle communication while in a convoy, or to communicate to Molly while out for a walk. The 2m band is well suited to reliable local communication and is an excellent choice for overlanding.

Point-to-Point or Radio-to-Radio communication in the HAM radio world is called Simplex. The main advantage of Simplex is that it does not require a local repeater, and can therefore work anywhere, you just need two radios.

A repeater is a radio station, typically located on a tall building or mountain top that takes low power signals from HAM radios and re-transmits them at a higher power level. The extra height and extra power means the signal can travel much further.

The disadvantage of Simplex is that communication distance is limited by the curvature of the earth and the height of each antenna above the ground. The antenna on Molly is located on the front of the truck. While not a perfect location for radio wave propagation, it is a good place for the antenna as it is low enough avoid it being damaged by low hanging branches. The handheld radio has a short rubber-ducky antenna.

D-Star Digital Communication.

There are many ways for one radio to communicate with another. Analog is very popular, but we decided to base our radio communication on digital. Within the Amateur radio world there are three different digital systems, we chose the D-Star system. Analog or either of the other two digital systems would work just as well for overlanding.

Digital has the advantage that the audio quality is really good. But this is not the main reason we went with a digital system. D-Star allows simplex and repeater based communication, and it also allows a radio to link through an internet gateway to communicate all around the world. This seems like a really cool idea while overlanding.

Sending and receiving GPS Coordinates.

Overlanding is all about where you go; having a radio that can transmit and receive GPS coordinates allows us to know where each radio is. This could be a radio in another vehicle or a radio with some out for a walk. The GPS coordinates can be sent to the internet to be displayed on live map, or just sent locally to anther radio to show how far away someone is. In our case we also log the coordinates to our on-board computer.

D-Star supports sending GPS coordinates during normal voice communication. No need to do anything fancy, just talking to the radio in Molly will display how far away the other radio and therefor person is. The radios can also be set-up to beacon, which involves sending the GPS coordinates on a regular schedule, say every 10 minutes. The Kenwood TH-D74a also has another digital feature called APRS, which is yet another digital mode, slightly different than D-Star, that also can beacon GPS coordinates, as well as exchange messages and even email with other HAM operators. We are probably not going to use the message and email features.

Antenna mounted on the front brush guard.
The Details.

The above shows that HAM radios are helpful for vehicle to vehicle communications, or for when someone is away from the vehicle and wants to talk to someone at Molly basecamp, or even to talk to someone half way around the world. And, while talking to others, without doing anything special, you can share your location, so they know where or how far away you are. Setting this all up is quite easy, but there are always a few tricks. The following is a blow-by-blow description with more details than you might want.

ICOM ID-5100A Dual Band Mobile
Kenwood TH-D74a Tri Band Handheld

The ICOM ID-5100A radio is located in the house. In our case, Molly acts as our basecamp-on-wheels and we use the radio when we have stopped and have made camp. So, it is more useful to have the radio in the house than the front of the truck. We use our Kenwood TH-D74a handheld when driving for talking to other vehicles.

The base unit is safely secured in our electrical cabinet. currently the base unit is powered off a 12 volt power supply connected to the inverter. The long term plan however is to power the base unit off the house batteries. But still looking into changing the AGMs into Lithiums, which will provide a flatter drop off curve.

Connected to the base unit are the microphone, a speaker, the display or head unit, a data connection to our computer and of course to an external antenna. The head unit and microphone are located away from the base unit and we used extension cables. IN our case we used ICOM IC-OPC-440 and ICOM IC-OPC-1156.

The antenna is a Diamond model NR770HNMO which is located on the front bumper. This location gives a reasonable height above ground without the antenna getting constantly damaged by low hanging branches. The ground plane for the antenna is frankly terrible, but good enough for our purposes.

The data connection between the ID-5100A and the computer uses an RT Systems RTS05 cable, which converts the RS-232 transmit (TXD) and receives (RXD) signals into USB. Fortunately the linux computer had the right drivers for this cable. The ID-5100A data port can be used for lots of different things, we have it set up to output GPS coordinates received from other D-Star radios.

Refer to the Low speed data communication in section 7 of the ID-5100A manual for setup details. In complete irony, the best way to output DPRS GPS signals is by setting “GPS Out” to “OFF: (page 12-20 for details). If you have this set to “ON”, then the GPS location of the ID-5100A will be sent out the data port, and this prevents the DPRS GPS coordinates being sent out.

Although the linux system recognized the RTS05 cable, for some reason it did not default to the correct baud rate. The command sudo stty -F /dev/ttyUSB0 9600 fixed this. Or alternatively node-red can be used to connect to the serial port.

The following is an example of GPS data received on the ID-5100A from the TH-D74a as presented on the data output port


The base unit has as built-in speaker, but of course it is hidden away in the electrical cabinet, and this makes it very hard to hear. An external speaker could be anything; but we opted to wire it into the existing Earthcruiser speaker systems with an in-line bluetooth and amplifier. This avoids having to mount a new speaker. additionally, the base unit has a noisy fan which turns on during transmissions, yet another reason for an external speaker.

This unit allows us to connect the Radio to the house speakers, along with 3 bluetooth devices.

The ID-5100A is a D-Star radio and therefore it can use the D-Star network to communicate to any other D-Star radio connected to the D-Star network. Molly just needs to be in radio range of a D-Star Gateway. In New Zealand we have no nearby D-Star Gateways, so we made our own D-Star hot-spot with an OpenSpot2 from RF Shark.

The Kenwood TH-D74a handheld radio is configured to send NEMA based GPS sentences over DPRS back to the ID-5100A located in Molly. This allows the ID-5100A to display how far away the TH-D74a is, but better still, the ID-5100A sends these same GPS coordinates to the computer which can log and display the location on our map server. So, when talking to each other with our radios, we always know how far away the other is.

Information shown on the ID-5100A when the TH-D74a sends GOS coordinates over D-Star and DPRS.

Unfortunately the same does not work the other way around. Although the TH-D74a (handheld) receives the GPS coordinates from the ID-5100 (base radio), it does not automatically display the location of Molly on the TH-D74a screen during the call. Maybe Kenwood will add this feature one day. It is however possible to look through D-Star RX (receive) log on the TH-D74a and find the position reported during the call.

GPS Position is available in the RX (Receive) log.
The TH-D74a has really good GPS information with APRS, but none of these screens are available with DPRS (unfortunately)

Both the ID-5100A and the TH-D74a can tune to the Weather bands and get weather reports and forecasts. If an APRS capable repeater is nearby, then a weather report can be requested from WXBOT, which is a weather bot.

WxBot is an APRS-IS listener app that listens for messages and responds with a brief US National Weather Service forecast.  International users note, Metar and CWOP are the only useful queries for locations outside of the United States

Refer to the Weather Bot website for more details.

The TH-D74a can also monitor the APRS network, where HAM Radio Operators can transmit their location on frequency 144.390MHz. So now, the location of our handheld as well as other HAM Operators can be displayed on our computer map.

The GPS coordinates sent to the computer can be displayed on a browser.

The format of the Waypoint can be set in TH-D74a at menu 540. The following is an example of the Kenwood format


$PKWDWPL, is the sentence identifier
070233,   is the UTC time in hhmmss format
A,        is a Valid reading. It is always A
3752.66,  is the latitude
N,        is North, but could be South
12217.83, is longitude
W,        is west, but could be East
0,        is speed in knots
327,      is course in degrees 
300120,   is the UTC date in dummy format
000016,   is altitude in meters
KM6UAP-9, is HAM Operator callsing
\\        is the APRS symbol
*64.      is the checksum