RADIO COMMUNICATION FOR OVERLAND CONVOYS AND. TRIPS. Covers matters related to convoy working with radio's, Antennas, GPS’s and. Long distant email. Author: Anton Matthee Terms: Range for reliable communication: This is the distance over which communication is possible in most cases and independent of different types of terrain that is presented during an Overland trip

Types of radio's for convoy working: There are basically two means of convoy radio communication used by the Overland fraternity: • 29 MHz radio, • VHF radio (normally between 130Mhz-170Mhz)

Overview of convoy radios: 29Mhz These type of radios are widely used by the Overland feternity and has a 3 km range for reliable comms. It does not really matter how much power you transmit the range stays more or less the same. Distances of up to 20km has been achieved under special circumstances. The characteristics of a 29Mhz radio wave are such that it DO NOT want to travel as a ground wave between cars. Field tests confirm that it does not matter how much power (or watts) you transmit from a 29 Mhz radio the radio waves will propagate up to the ionosphere within a few kilometers (Ref: propagation mode at http://en.wikipedia.org/wiki/Radio_propagation ). This is the reason why this frequency was allocated to 4x4 convoy use in that it will not interfere with other stations that are 10 or 20km’s away. 29Mhz radios use AM modulation and is prone to interference e.g power lines, spark plugs, etc and can present audio that is not clear at times. Channel 14,15 and 16 are assigned to 4X4 / Overland use. VHF

These type of radios are NOT currently widely used by the Overland feternity but has a 10km range for reliable comms with 25-50 Watts. Distances of up to 100km has been achieved under special circumstances. A VHF radio wave’s propagation characteristics are such that it can only travel in a straight line (also called line-of-sight) meaning that the receiver and transmitting station should have an unobstructed path between them. There is a non-linier relationship between power and range/distance in the VHF frequency range. Field tests confirm that if you increase the power by ten times (e.g. from 10 to 100 watts) the distance will roughly double (e.g. from 10 to 20km). VHF radios use FM modulation and is very robust against power line interference and present clear speech.

Handhelds vs. mobile sets for convoy working (applicable to 29Mhz and VHF) A handheld is an easy option to take on trips because one does not have to mount an antenna and can also use it outside of the car (ideal for trying to give directions to the convoy coming into a campsite). Field tests show that the range of these handhelds is much less if compared to their mobile counterparts. A practical range for a 29Mhz handheld in a convoy situation is 1 km and for VHF about 5km. An outside antenna does help but the lower wattage of the handheld radios is not sufficient to get the same range as a mobile set especially in the case of a VHF set.

Should I buy a 29Mhz or a VHF radio for Overland convoy communications? You should buy a radio that is the most used by the group that you are traveling with. In general Overlanders currently use the 29Mhz standard (although inferior in range to VHF). VHF radios are becoming more popular but it is estimated that less than 5% of Overlanders currently (2006) use the VHF standard for convoy comms on Overland trips. A 29Mhz radio cost +-R900 and a good second hand VHF radio can be sourced for +-R1500. New VHF radio's can cost anything from R1500 to R2500. Can I buy an older 29Mhz or VHF radios? In both 29Mhz and VHF one gets older makes of radios that use discrete components. These radios are normally bigger and cheaper than the modern sets. Radios that use discreet components tend to have a high failure rate on an Overland trip as the components vibrate loose or break.

It is best to rather buy one of the modern radios that use Surface mount technology (SMT) as these components cannot vibrate relative to their mounting points. These radios are much smaller than their “discreet component” counterparts and take up less space in your vehicle. Why use a radio in a convoy? There are different practical applications why it is important to have radios between the cars of a convoy on an Overland tour: -

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Radios save a lot of time: Time management is one of the most important aspects of an Overland tour. Radios can be used to share and discuss information, make plans, arrange events such as stops, etc. whilst on the move; Radios are used for convoy safety: It is common practice for the leader of the convoy to warn the rest of the vehicles of a danger on the road; Co-ordinate movements of convoy members within towns; Break the boredom of long roads; etc.

Antenna position on car: Theory about antenna placement: An antenna needs a “ground” plane to operate and for mobile applications the vehicle serves as this ground plane. A normal vertical mobile antenna will radiate best to the direction of the largest ground plane meaning that if you mount your antenna at the right front it will radiate towards the left rear of the car. Refer to figure (5.21) below.

Practical experience of antenna placement for convoy applications: Field tests on 29Mhz and VHF showed that the position of the antenna on the car matter very little for convoy working. Mount the antenna where it is practical. The more height you can get from your VHF antenna the further the range. As a general rule one can then deduct that it would make a difference to mount your VHF antenna on your roof. It is less important where you mount your 29Mhz antenna as the propagation characteristics is such that it want to propagate up into the ionosphere rather than directly to another vehicle. An interesting fact is that VHF signals that are transmitted from satellites of between 5-20 Watts are received on earth over distances of 1000-3000km. VHF repeaters on mountains can be received up to a 100km. Height for VHF = Distance. If you cannot communicate on VHF from one vehicle to another it will help to drive up a mountain/koppie to get some height and try again.

Radios and GPS’s – is there any synergy? Most Overlanders use both GPS’s and Radios in their vehicles. Is there ways in which these two devices can be used synergistically? YES. Load the same route onto all the GPS’s in the convoy. Navigate/activate the same route on all the GPS’s (use “off-road” option for auto routing GPS’s). All the GPS’s will now track with a straight line to the same reference point

which will be the next route waypoint. All of the GPS’s will also display a distance to the next waypoint. This distance can be used by the leader of the convoy to call a marker to the rest of the convoy e.g “Donkeys at 14.26km”. All the convoy members behind the leader will then know exactly where the danger is. This method of calling markers also works excellent to indicate splits and turns e.g. “Split left at 9.88km”. If the next route waypoint is reached all the GPS’s will automatically adjust to the next route waypoint and so on….. This method also works to determine the length of a convoy e.g the leader of the convoy only need to ask the person at the back of the convoy for a marker and then subtract it from his own marker and the difference then indicates the length of the convoy. These methods might sound complicated but it is not and if you use them once you will definitely use them again. This method works best. If the route waypoints are at least 10km from each other.

Email in the Bush Emails can be sent whilst Overlanding by using a Laptop+radio modem+HF Radio+HF antenna. The radio transmission is sent to a HF Gateway where your email is received and then relayed to the Internet. The equipment required in your vehicle are: -

HF Radio and antennas - +-R8000 Radio modem – +-R8000 (ref www.scs-ptc.com) Laptop email software (normally free)

The cost of this system is prohibitively high. The Radio Ham network is referred to as Winlink or Airmail and works on a network that is supplied by Ham stations across the world. Southern Africa has two of these gateways – one in Pretoria and the other one in Pietermaritzburg. Only licensed radio hams can use this network and it is free of charge. Upon registration with Winlink you receive an email address “callsign”@winlink.org The commercially alternative of “Winlink” is referred to as Bushmail. It uses the same type of equipment but it is a different network as the Winlink network. Any person can register with Bushmail and use this system but it costs between USD 500-1000/year for subscription fees. It is believed that they have their gateway in Maputo. You can also use Airmail email software to send position reports to an international positioning database (www.findu.com ). These positions can

be displayed on a map and are accessible over the Internet look here. Green lines link the different position reporting points in this example. You can attach files/photos to your emails as well. The speed of the link when sending emails depends on the propagation conditions of the frequency that you use. Under normal conditions the speed is similar to a 1200 baud modem and it takes anything from 2-5 minutes to send a 50KB email. Propagation conditions are such that you will use the system during day time hours on 7Mhz-21Mhz depending on your distance to the gateways. For more information on Winlink: http://www.radioministries.org/winlink.htm#station http://www.airmail2000.com/pprimer.htm

For more information on Bushmail: http://www.bushmail.co.za

Also refer to http://www.overland.co.za/2WayRadios/ for additional information about radio's and. licensing