RANGE ACHIEVABLE WITH 29 MHz RADIOS BASE STATIONS: In practice one can achieve about 20km with a base station or vehicle mounted radio coupled to a good antenna. All the below factors can limit this distance. Factors that influence range are:


Output Power - Output power is limited to 5 watts max by legislation. Virtually all 29 MHz radios have output power ratings of between 4 and 5 watts.




Antenna - An antenna is possibly the item that most affects range. A good antenna efficiently converts electrical energy from the radio into electro-magnetic (radio) waves. A very rough guide is “the longer the better”. This rule of thumb only applies to antenna specifically designed for use on 29 MHz will not work well at all.




Terrain-At 29 MHz, radio waves do not pass through buildings easily. Dense forests also shorten range and bushveld to a lesser extent. A hill or ravine can completely block a signal.




The Horizon-29 MHz communication is generally “line of sight”. The best range achievable therefore is effectively just beyond the horizon.

HANDHELDS: Hand-held 29 MHz radios have short “rubber duck” antennas that limit their range to a maximum distance of about 2km to 4km. In a vehicle the range can be as little as 100 meters because of the screening affect of the vehicle’s metal body. This can be overcome by using a Car Adapter Kit that couples the hand-held radio to an external antenna and to the car’s battery. Under these conditions the hand-held radio can perform almost as well as a vehicle mounted radio.

DIFFERENCES BETWEEN 29MHZ AND VHF – FOR 4x4 29MHz: Pros







Signals travel far Can talk to anyone that also has 29Mhz If you are lost, good chance to find help Draws little amps out of the batteries makes the route more interesting for 4x4 enthusiasts to be able to talk with others and tour guide can give advice and info while driving. Radio license is much cheaper.

Cons





Signal quality is not good but clear Cannot have private talks Cannot connect to repeater Squelch needs to be turned up to obtain far signal. (very noisy)

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VHF: Pros




Excellent sound quality Can connect to repeater which enables distance conversations, e.g. Cape Town to Johannesburg Can have private talks when connected on the same frequency

Cons





High amps are drawn out of battery The signal distance without repeater is not very far Repeaters are costly Repeaters do not work outside country or mountain ranges.

ANTENNAS Several types of vehicle-mounted antennas are available. Below are the pros and cons of each type.

They are named according to their physical characteristics, from the basic Whip antenna, which is normally ¼ Wavelength long or roughly 2.75 meters. The other antennas are shorter, but to achieve the required length, the designers include a small coil either at the base of the antenna (Base Loaded) or in the centre of the antenna (Middle Loaded) or at the top (Top Loaded).

Type

Pro's

Con's

Whip Antenna

Best Reception.

Excessive length, sways excessively and, due to it's strength, removes lights in parking garages.

Base Loaded

Good reception, does not sway excessively, fairly robust.

Longer than Top Loaded, so still tends to hit lights in parking garages.

Middle Loaded

Shorter Antenna, good reception.

Sways around badly due to weight of coil, low hanging branches tend to damage the coil.

Top Loaded

Shorter Antenna, excellent reception.

Sways around badly due to weight of coil, low hanging branches tend to damage the coil.

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Antenna Placement This is a very emotional issue as it normally means drilling holes in your vehicle. For the antenna to function effectively a “ground plane” is required. This is any conductive grid, to which the unshielded ground cable can be attached. A non-technical explanation says that the antenna propagates the radio waves and “bounces” them off this ground plane into the atmosphere. In our case, the vehicle surfaces form this “ground plane”, so the best place for the antenna is in the centre of the roof at the highest point. With military vehicles or dedicated Off-road vehicles, the placement of the antenna in this position is fairly easy. However for our use, it is not, so some compromises are required. Here are the pointers. The antenna should be mounted:






As high as possible. As close to the center of the vehicle as possible. As far from interference from engine components as possible. Must be well earthed. Must not be "shielded" by vehicle surfaces.

Some of these are achievable even on our vehicles, but then we hit practical problems such as the antenna removing lights in parking garages, or getting wiped out by passing trees. This really leaves us with three options. The first option and also the worst from a reception point of view, is a base/middle or top loaded antenna fitted to one of the front fenders. In this case the top loaded antenna is normally the shortest and is short enough to miss most overhead lights etc, but sways around very badly. The reception is also affected by which fender it is located on, as the “ground plane” will be missing on one side thus giving worse reception to one side. Having said all that, this remains the most practical option for permanent mounting for recreational purposes. This will normally work for general convoy use, but severely restricts the range. The second favored option is to mount the antenna on the roof of the vehicle using a “Gutter Clamp”. The Gutter clamp makes the antenna removable and does not require holes to be drilled. A problem is that antennas are often destroyed by low hanging bushes and branches when fitted to roof racks and gutters. Here the choice of Antenna itself is open, but probably the best is the base loaded antenna due to its reduced “sprung” weight. This means that it will not sway as much and is mechanically more able to take the knocks. This option will also provide different reception depending on which gutter is chosen, unless the vehicle is fitted with a gutter over the windscreen. Mounting the antenna in the centre of this gutter provides the almost ultimate spot. Some “Gutter Mounts” incorporate a method by which the antenna can be tilted without removing them from the gutter, should you wish to go into places with lower clearance. The third option is to mount the Antenna on the Bush bar. This is a very practical mounting, does not require holes in the bodywork, but has severe restrictions in forward transmissions due to the lack of Ground Plane. Antennas should always be mounted so that the minimum length of the antenna is shielded by the vehicle’s bodywork. Very Important: Never key the radio with the antenna tilted, removed, disconnected or touching any metallic parts of the vehicle, as this will most likely blow the output transistors of the radio.

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Antenna Fitment Once we have decided where to fit the antenna, the following tips will help you achieve maximum performance for your chosen spot.






Beware that the antenna must be mounted so that the steel part of the antenna will never come into contact with parts of the vehicle while transmitting or the result will be damage to the radio. The Antenna cable does not normally have a Radio Adaptor fitted, so make sure that one has been supplied according to the requirements of your radio. This makes it easier to route the cable, as a smaller hole will be required. Before fitting the antenna to the vehicle ensure that the paint is removed from the clamping area (underneath, where it cant be seen) so that a good antenna earth will be established. Where antennas are mounted on a canopy, an earth braid (braided cable) may be required to connect the antenna base to the nearest vehicle bodywork. Steel canopies must be grounded to the body of the vehicle by means of an earth braid. Once the cable has been routed to the radio, the correct Adaptor can be fitted. This requires some skill with the soldering iron. Make sure that the co-axial earth screen does not touch the centre core, as this dead short will blow the output transistors of your radio at least. The connections must be electrically sound and mechanically strong to withstand vibration and movement. A short piece of “heat shrink” is recommended for finishing off the connection.

Antenna Tuning





The Antenna should be supplied with a Cutting Sheet. This will provide a clue to the correct Antenna length per frequency. Carefully study the Cutting sheet. Make sure you understand, the required length, from where to where it is to be measured, and that you are looking at the right frequency. Choose a Frequency in the middle of the range of frequencies you intend to use it on. Once you have determined these issues, proceed to cut the antenna at exactly (or a fraction longer) the indicated length. If you have an SWR meter available, cut the antenna 1 to 2 cm longer than required and then using the SWR meter, gradually cut small pieces off until achieving the best SWR. DO NOT CUT TOO MUCH OFF or you will ruin the antenna.

Multi-purpose Antennas While there are some multi-purpose antennas on the market such as combined FM/27MHz or FM/29 MHz antennas, they are not recommended as their performance is a compromise and neither operation is optimised. FM should preferably have it’s own antenna. Two choices are offered for those who wish to use multiple frequency radios in their vehicles.





The Antenna Tuner / Matching Unit (Balun). This device allows the antenna to “tune” itself to the frequency of the radio and maintains an impedance of 50 Ohms at all times. Some power loss does occur and when working with a mere 5 Watts, this can be critical. When working on HAM applications where high power is applied, this loss is negligible, so this device is recommended for HAM use not 29MHz. Swopping Antennas. When purchasing antennas for your vehicle, buy one base and then select your antennas so that they all fit the same base. The Antenna Manufactures can help you with this. Basically this affords the luxury of one mounting point (or hole in the vehicle) and the ability to swop antenna’s according to the frequency spectrum of the radio in use. This method is a little more trouble, but ensures that you get all the power to the antenna and out into the atmosphere.

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Magnetic Mount Antennas Although they look like a blessing in disguise, as they can be used at will, please remember the following traits: They do not earth to the bodywork, so power output / ground plane is not as good as other mounting options. They tend to scratch the paintwork especially if they get dust in-between the mounting and the bodywork. They don’t adhere to aluminium-bodied vehicles at all. But they can be removed when not in use, so no unsightly holes, mounting brackets and antennas when using the Landy to the shopping mall. They are easily removed by passing trees and members of the “plaaslike bevolking”.

RADIO LICENCES Who and what is licensed? All and any communications equipment must be licensed. In the case of the first two “types” radios, mentioned above 29 MHz, the radio is licensed. Who is the licensing authority? ICASA (Independent Communications Authority of South Africa) provides us with all licenses. For more information, visit the following link, http://www.icasa.org.za What are the licensing requirements for a 29 MHz? With a 29 MHz radio used privately, the radios need to be licensed. You will have to apply for the radio license from ICASA and once you have received the license, you can pick up your radio. ICASA will require the name and model of the radio. Note: Killerdeals will assist with new License applications & will supply Radio with completed application. 29 MHz Radio Channels

CHANNEL #

FREQUENCY (MHz)

1

29.7100

Mobile

2 3

29.7225 29.7350

Mobile Mobile

4 5

29.7475 29.7600

Civil Emergency 1 Mobile

6 7

29.7725 29.7850

Non commercial boats at sea and inland waters Mobile

8 9

29.7975 29.8100

Mobile Mobile

10 11

29.8225 29.8350

Civil Emergency 3 Mobile

12

29.8475

Civil Emergency Calling

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13

29.8600

Mobile

14 15

29.8725 29.8850

ORRA Mobile

16 17

29.8975 29.9100

ORRA Mobile

18 19

29.9225 29.9350

Fire Fighting (Rural) Civil Emergency Safety of small vessels at sea and onland shores

20 21

29.9475 29.9600

Civil Emergency 2 Mobile

22 23

29.9725 29.9800

Boats at sea and inland waters Government

IMPORTANT NOTES: You are entitled to use the channels appearing on your licence, for example: The farming community generally use channels 12, 4, 20, 10 & 18 and are usually allowed the use of one mobile channel. SKI-BOATS: Use channels 19, 6 & 22, in that order. 4x4's: Use channels 14, 15 & 16. Visit the following links for more interesting information on radios



http://www.orapabushclub.50megs.com/radio/radio.html http://www.beadbreaker.co.za/radio_qa.htm

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