I would like to present an “easy to follow” article on Two-Way Radios and Licensing procedure. In a short article such as this, one cannot present all, but hopefully enough to help clear some confusion.
Some of this article has been culled from previous articles, I will try weed out the repetition as I go along.
WHAT TYPE, 29MHz AM or FM?
29MHz AM RADIOS
The virtues of 29MHz AM radios are many – they are relatively cheap and many Clubs and 4x4 drivers make use of them. They are priced at around R800 – R1100 excluding antenna & installation. Their reliable operating range is anything from about three to fifteen KM or thereabouts, but this varies greatly with weather conditions and time of day, as well as area of operation and motor vehicle suppression..
Pros: Relatively cheap; fairly popular and in common use by many Clubs & Organisations. Licences quick & easy to obtain.
Cons: Very few Manufacturers of these units as it is no longer considered a serious Commercial product. Reception is hampered by poor weather conditions and electrical impulse noise, particularly with petrol engines.
Antenna location is important with AM, a permanent mount is to be preferred over a magnetic mount, and ideally the antenna should be mounted in the middle of a large expanse of metal, such as the roof of a double-cab. This might not always be convenient, and mounting the antenna elsewhere could result in directional RF radiation. Usually, you could always expect up to 5Km useful coverage between two
like units.
Photo of Dragon KR-80 AM Radio
FM RADIOS
The most common FM radios operate on VHF, which is a range of frequencies within the 146-174MHz band. FM radios offer very good distances, anywhere from about 25-50Km between mobile units but once again dependent upon terrain! They are powered at 25W RF and are relatively immune to interference caused by atmospheric or electrical conditions. The radios are not freely available over the counter however, because of stringent ICASA licensing requirements. Upon receiving a Licence, you will not be granted a country-wide frequency, but one for your own private use and it will not necessarily be the same as that in use by any Club or other user. In fact, other than joining the local chapter of a 4x4 Club and making use of their allocated frequency, you might consider getting together with some local pals and forming your own 4x4 club, writing a constitution, and obtaining a licence in the name of your new club. More on this later.
An advantage of a multi-channel FM radio is the ability to operate on your Business Frequency, should you so desire, as well as the "recreational" frequency. Therefore, the Taxman should pay for your radio if you have a Business application for it as well
.
Pros: Extended range, high-power RF, clear reception, modern communication tool
Cons: Price varies from R1800-R2000 excluding antenna & installation. Waiting period of some 6-8 weeks for ICASA licence, not yet in common use by 4x4 users.
The same rules for AM antennas apply to the FM antennas as well. However, there are two common types available:
* Quarter Wave Antenna, which should once more be mounted in a central position on a metal surface, but is only some 400mm or so in length, and
* 5/8 Antenna, normally side- mounted on the door pillar behind one of the doors. This type of antenna is designed for this application and will produce good results.
Of the two types, I prefer the former for mountainous terrain, the latter for flat countryside.
Pictured below are two typical VHF/FM Radios, the Kenwood TK7102 4-Channel unit, and the Vertex VX2100 8-Channel radio. Both radios feature Channel Scan if required.
KENWOOD TK7102 4-Channel VHF Radio
VERTEX VX2100 8-Channel VHF Radio
HANDHELD RADIOS
I am not discussing the 29MHz hand-held portable radios here as they are totally impractical for 4x4 usage and their long aerials are cumbersome. They have a very limited operating range and are no longer readily available.
i) Licence Free
The cheapest radios are the so-called “Licence Free” hand-held radios, which have very limited RF output stages, usually somewhere between 50mW & 500mW. Dump the 50mW, they are worthless. The 500mW radios offer an operating range of anywhere between 1 – 3Km, depending upon terrain, irrespective of what their Manufacturers might like to claim on the packaging. Line of sight provides the best range. They are powered by three or four penlight cells and are usually supplied with rechargeable Ni-Cad battery packs and a battery charger. Useful for short-range communication, not all that useful for communication between two or more vehicles except when within a few hundred metres from each other.
Pros: Price
Cons: Not really designed for serious radio Communication, but very useful for low-cost short-range communication..
ii) Pre-Licensed
ICASA (the SA Regulating Authority on Radio Communications equipment) have granted certain Companies permission to sell portable handheld radios that have been pre-licensed, i.e. the fees for the first year are included in the radio’s selling price. These radios have a greater RF output than those mentioned above, being typically 2 Watt units. They are professional radios and are priced at three or four times the price of the licence-free radios. Typical operating range is from 3 – 5 KM, although longer ranges have been reported in good conditions. Again, line of sight works best. The radios are supplied with a Ni-Cad battery pack & a 220V charger, although the chargers can be modified for 12v charging with certain limitations.
Both the above types operate within the UHF frequency range, 450 – 470MHz.
Pros: Better range that the Licence-Free radios
Cons: Possibly price, but you are buying a premium product!
Pictured hereunder is the HYT TC1688 Licence-Free Portable Radio.
HF/SSB RADIO:
These high-power radios operate on low RF frequencies, typically between 1.8 ~ 30MHz, at RF levels of about 100W. They offer greatly extended operation, but they do have pitfalls. The operating range varies with a local ground-wave signal providing about 30Km radius, but this is in general not too reliable and nor is the radio designed for ground-wave communications. HF comes into its own with the reflected Sky-wave signal, which signal that is reflected off the Earth’s Ionosphere, which is constantly varying in height from above the Earth’s surface. The RF path can be compared to a tennis ball bouncing up and down as it is thrown hard into the ground.
The distances obtained by HF are virtually anything from 300Km upwards but the operating frequency (and therefore operating range) is very much influenced by the height of the Ionosphere at the time of transmission and therefore these radios are generally allowed to operate on three or four frequencies to allow for the changing conditions. Weather conditions play a major part in obtaining clear reception, as the system is essentially an AM one. Atmospherics and Lightning would cause difficult reception, as would electrical impulses.
Because of the need for various operating frequencies, you will have to consider using an “Automatic Antenna Tuner”. Each operating frequency requires the antenna to be a certain fixed length to provide for maximum signal transfer and also to prevent damage to the radio. This is done either by the use of an Automatic Antenna Tuner, or you could carry four stainless steel whips & HF Coils and change them as you change frequency – not too practical!
HF/SSB licences, although obtainable, are fairly restricted due to the limited number of available frequencies. This is not a bad thing in itself, as it is comforting to know that there might be other users on the same frequency should you be stranded in a remote area and in need of assistance. You are allowed to use HF across borders, provided you have the necessary Radio Communications Licence from both Country’s Regulatory Authorities.
Successful HF radio operation requires a learning curve, but for those traveling long distances where there is no other means of communication, it is a blessing.
Pros: Greatly enhanced RF coverage
Cons: Price, adversely affected by bad weather, long antenna/s
KENWOOD TK90 HF/SSB Radio
VERTEX VX2100 HF/SSB Radio
No comments:
Post a Comment